Apr. 2018 Ocean Cooling Delayed

globpop_countries

The best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

  • The ocean covers 71% of the globe and drives average temperatures;
  • SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
  • A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through April 2018.

HadSST042018

A global cooling pattern has persisted, seen clearly in the Tropics since its peak in 2016, joined by NH and SH dropping since last August. Upward bumps occurred last October, in January and again in March and April 2018.  Four months of 2018 now show slight warming since the low point of December 2017, led by steadily rising NH.  Only the Tropics are showing temps the lowest in this time frame, despite an anomaly rise of 0.14 in April. Globally, and in both hemispheres anomalies closely match April 2015.

Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back below its beginning level. Secondly, the Northern Hemisphere added three bumps on the shoulders of Tropical warming, with peaks in August of each year. Also, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.

With ocean temps positioned the same as three years ago, we can only wait and see whether the previous cycle will repeat or something different appears.  As the analysis belows shows, the North Atlantic has been the wild card bringing warming this decade, and cooling will depend upon a phase shift in that region.

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

HadSST95to042018

Open image in new tab for sharper detail.

1995 is a reasonable starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16, with July 2017 only slightly lower.  Note also that starting in 2014 SH plays a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years as shown by this graph:

The data is annual averages of absolute SSTs measured in the North Atlantic.  The significance of the pulses for weather forecasting is discussed in AMO: Atlantic Climate Pulse

But the peaks coming nearly every July in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.Now the regime shift appears clearly. Starting with 2003, seven times the August average has exceeded 23.6C, a level that prior to ’98 registered only once before, in 1937.  And other recent years were all greater than 23.4C.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up?

To paraphrase the wheel of fortune carnival barker:  “Down and down she goes, where she stops nobody knows.”  As this month shows, nature moves in cycles, not straight lines, and human forecasts and projections are tenuous at best.

einsteinalbert-integratesempirically800px

Postscript:

In the most recent GWPF 2017 State of the Climate report, Dr. Humlum made this observation:

“It is instructive to consider the variation of the annual change rate of atmospheric CO2 together with the annual change rates for the global air temperature and global sea surface temperature (Figure 16). All three change rates clearly vary in concert, but with sea surface temperature rates leading the global temperature rates by a few months and atmospheric CO2 rates lagging 11–12 months behind the sea surface temperature rates.”

Footnote: Why Rely on HadSST3

HadSST3 is distinguished from other SST products because HadCRU (Hadley Climatic Research Unit) does not engage in SST interpolation, i.e. infilling estimated anomalies into grid cells lacking sufficient sampling in a given month. From reading the documentation and from queries to Met Office, this is their procedure.

HadSST3 imports data from gridcells containing ocean, excluding land cells. From past records, they have calculated daily and monthly average readings for each grid cell for the period 1961 to 1990. Those temperatures form the baseline from which anomalies are calculated.

In a given month, each gridcell with sufficient sampling is averaged for the month and then the baseline value for that cell and that month is subtracted, resulting in the monthly anomaly for that cell. All cells with monthly anomalies are averaged to produce global, hemispheric and tropical anomalies for the month, based on the cells in those locations. For example, Tropics averages include ocean grid cells lying between latitudes 20N and 20S.

Gridcells lacking sufficient sampling that month are left out of the averaging, and the uncertainty from such missing data is estimated. IMO that is more reasonable than inventing data to infill. And it seems that the Global Drifter Array displayed in the top image is providing more uniform coverage of the oceans than in the past.

uss-pearl-harbor-deploys-global-drifter-buoys-in-pacific-ocean

USS Pearl Harbor deploys Global Drifter Buoys in Pacific Ocean

 

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Mar. 2018 Ocean Cooling? Wait and See

 

globpop_countriesThe best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

  • The ocean covers 71% of the globe and drives average temperatures;
  • SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
  • A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through March 2018.
HadSST032018

A global cooling pattern has persisted, seen clearly in the Tropics since its peak in 2016, joined by NH and SH dropping since last August. Upward bumps occurred last October, in January and again in March 2018.  Three months of 2018 now show slight warming since the low point of December 2017.  Only the Tropics are showing temps the lowest in this time frame.  Globally, and in both hemispheres anomalies closely match March 2015.

Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back below its beginning level. Secondly, the Northern Hemisphere added three bumps on the shoulders of Tropical warming, with peaks in August of each year. Also, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.

With ocean temps positioned the same as three years ago, we can only wait and see whether the previous cycle will repeat or something different appears.  As the analysis belows shows, the North Atlantic has been the wild card bringing warming this decade, and cooling will depend upon a phase shift in that region.

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

HadSST1995to032018

Open image in new tab for sharper detail.

1995 is a reasonable starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16, with July 2017 only slightly lower.  Note also that starting in 2014 SH plays a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years as shown by this graph:

The data is annual averages of absolute SSTs measured in the North Atlantic.  The significance of the pulses for weather forecasting is discussed in AMO: Atlantic Climate Pulse

But the peaks coming nearly every July in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.Now the regime shift appears clearly. Starting with 2003, seven times the August average has exceeded 23.6C, a level that prior to ’98 registered only once before, in 1937.  And other recent years were all greater than 23.4C.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up?

To paraphrase the wheel of fortune carnival barker:  “Down and down she goes, where she stops nobody knows.”  As this month shows, nature moves in cycles, not straight lines, and human forecasts and projections are tenuous at best.

einsteinalbert-integratesempirically800px

Postscript:

In the most recent GWPF 2017 State of the Climate report, Dr. Humlum made this observation:

“It is instructive to consider the variation of the annual change rate of atmospheric CO2 together with the annual change rates for the global air temperature and global sea surface temperature (Figure 16). All three change rates clearly vary in concert, but with sea surface temperature rates leading the global temperature rates by a few months and atmospheric CO2 rates lagging 11–12 months behind the sea surface temperature rates.”

Footnote: Why Rely on HadSST3

HadSST3 is distinguished from other SST products because HadCRU (Hadley Climatic Research Unit) does not engage in SST interpolation, i.e. infilling estimated anomalies into grid cells lacking sufficient sampling in a given month. From reading the documentation and from queries to Met Office, this is their procedure.

HadSST3 imports data from gridcells containing ocean, excluding land cells. From past records, they have calculated daily and monthly average readings for each grid cell for the period 1961 to 1990. Those temperatures form the baseline from which anomalies are calculated.

In a given month, each gridcell with sufficient sampling is averaged for the month and then the baseline value for that cell and that month is subtracted, resulting in the monthly anomaly for that cell. All cells with monthly anomalies are averaged to produce global, hemispheric and tropical anomalies for the month, based on the cells in those locations. For example, Tropics averages include ocean grid cells lying between latitudes 20N and 20S.

Gridcells lacking sufficient sampling that month are left out of the averaging, and the uncertainty from such missing data is estimated. IMO that is more reasonable than inventing data to infill. And it seems that the Global Drifter Array displayed in the top image is providing more uniform coverage of the oceans than in the past.

uss-pearl-harbor-deploys-global-drifter-buoys-in-pacific-ocean

USS Pearl Harbor deploys Global Drifter Buoys in Pacific Ocean

 

Media Raises False Alarms of Ocean Cooling

The RAPID moorings being deployed. Credit: National Oceanography Centre.

The usual suspects, such as BBC, the Guardian, New York Times, Washington Post etc., are reporting that the Atlantic gulf stream is slowing down due to climate change, threatening an ice age.  That’s right, warmists are now claiming fossil fuels do cooling when they are not warming.  As usual the headlines are not supported by the details.

The AMOC is back in the news following a recent Ocean Sciences meeting.  This update adds to the theme Oceans Make Climate. Background links are at the end, including one where chief alarmist M. Mann claims fossil fuel use will stop the ocean conveyor belt and bring a new ice age.  Actual scientists are working away methodically on this part of the climate system, and are more level-headed.  H/T GWPF for noticing the recent article in Science Ocean array alters view of Atlantic ‘conveyor belt’  By Katherine Kornei Feb. 17, 2018 . Excerpts with my bolds.

The powerful currents in the Atlantic, formally known as the Atlantic meridional overturning circulation (AMOC), are a major engine in Earth’s climate. The AMOC’s shallower limbs—which include the Gulf Stream—transport warm water from the tropics northward, warming Western Europe. In the north, the waters cool and sink, forming deeper limbs that transport the cold water back south—and sequester anthropogenic carbon in the process. This overturning is why the AMOC is sometimes called the Atlantic conveyor belt.

Fig. 1. Schematic of the major warm (red to yellow) and cold (blue to purple) water pathways in the NASPG (North Atlantic subpolar gyre ) credit: H. Furey, Woods Hole Oceanographic Institution): Denmark Strait (DS), Faroe Bank Channel (FBC), East and West Greenland Currents (EGC and WGC, respectively), NAC, DSO, and ISO.

In February at the American Geophysical Union’s (AGU’s) Ocean Sciences meeting, scientists presented the first data from an array of instruments moored in the subpolar North Atlantic. The observations reveal unexpected eddies and strong variability in the AMOC currents. They also show that the currents east of Greenland contribute the most to the total AMOC flow. Climate models, on the other hand, have emphasized the currents west of Greenland in the Labrador Sea. “We’re showing the shortcomings of climate models,” says Susan Lozier, a physical oceanographer at Duke University in Durham, North Carolina, who leads the $35-million, seven-nation project known as the Overturning in the Subpolar North Atlantic Program (OSNAP).

Fig. 2. Schematic of the OSNAP array. The vertical black lines denote the OSNAP moorings with the red dots denoting instrumentation at depth. The thin gray lines indicate the glider survey. The red arrows show pathways for the warm and salty waters of subtropical origin; the light blue arrows show the pathways for the fresh and cold surface waters of polar origin; and the dark blue arrows show the pathways at depth for waters that originate in the high-latitude North Atlantic and Arctic.

The research and analysis is presented by Dr. Lozier et al. in this publication Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System Images above and text excerpted below with my bolds.

For decades oceanographers have assumed the AMOC to be highly susceptible to changes in the production of deep waters at high latitudes in the North Atlantic. A new ocean observing system is now in place that will test that assumption. Early results from the OSNAP observational program reveal the complexity of the velocity field across the section and the dramatic increase in convective activity during the 2014/15 winter. Early results from the gliders that survey the eastern portion of the OSNAP line have illustrated the importance of these measurements for estimating meridional heat fluxes and for studying the evolution of Subpolar Mode Waters. Finally, numerical modeling data have been used to demonstrate the efficacy of a proxy AMOC measure based on a broader set of observational data, and an adjoint modeling approach has shown that measurements in the OSNAP region will aid our mechanistic understanding of the low-frequency variability of the AMOC in the subtropical North Atlantic.

Fig. 7. (a) Winter [Dec–Mar (DJFM)] mean NAO index. Time series of temperature from the (b) K1 and (c) K9 moorings.

Finally, we note that while a primary motivation for studying AMOC variability comes from its potential impact on the climate system, as mentioned above, additional motivation for the measure of the heat, mass, and freshwater fluxes in the subpolar North Atlantic arises from their potential impact on marine biogeochemistry and the cryosphere. Thus, we hope that this observing system can serve the interests of the broader climate community.

Fig. 10. Linear sensitivity of the AMOC at (d),(e) 25°N and (b),(c) 50°N in Jan to surface heat flux anomalies per unit area. Positive sensitivity indicates that ocean cooling leads to an increased AMOC—e.g., in the upper panels, a unit increase in heat flux out of the ocean at a given location will change the AMOC at (d) 25°N or (e) 50°N 3 yr later by the amount shown in the color bar. The contour intervals are logarithmic. (a) The time series show linear sensitivity of the AMOC at 25°N (blue) and 50°N (green) to heat fluxes integrated over the subpolar gyre (black box with surface area of ∼6.7 × 10 m2) as a function of forcing lead time. The reader is referred to Pillar et al. (2016) for model details and to Heimbach et al. (2011) and Pillar et al. (2016) for a full description of the methodology and discussion relating to the dynamical interpretation of the sensitivity distributions.

In summary, while modeling studies have suggested a linkage between deep-water mass formation and AMOC variability, observations to date have been spatially or temporally compromised and therefore insufficient either to support or to rule out this connection.

Current observational efforts to assess AMOC variability in the North Atlantic.

The U.K.–U.S. Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) program at 26°N successfully measures the AMOC in the subtropical North Atlantic via a transbasin observing system (Cunningham et al. 2007; Kanzow et al. 2007; McCarthy et al. 2015). While this array has fundamentally altered the community’s view of the AMOC, modeling studies over the past few years have suggested that AMOC fluctuations on interannual time scales are coherent only over limited meridional distances. In particular, a break point in coherence may occur at the subpolar–subtropical gyre boundary in the North Atlantic (Bingham et al. 2007; Baehr et al. 2009). Furthermore, a recent modeling study has suggested that the low-frequency variability of the RAPID–MOCHA appears to be an integrated response to buoyancy forcing over the subpolar gyre (Pillar et al. 2016). Thus, a measure of the overturning in the subpolar basin contemporaneous with a measure of the buoyancy forcing in that basin likely offers the best possibility of understanding the mechanisms that underpin AMOC variability. Finally, though it might be expected that the plethora of measurements from the North Atlantic would be sufficient to constrain a measure of the AMOC within the context of an ocean general circulation model, recent studies (Cunningham and Marsh 2010; Karspeck et al. 2015) reveal that there is currently no consensus on the strength or variability of the AMOC in assimilation/reanalysis products.

Atlantic Meridional Overturning Circulation (AMOC). Red colours indicate warm, shallow currents and blue colours indicate cold, deep return flows. Modified from Church, 2007, A change in circulation? Science, 317(5840), 908–909. doi:10.1126/science.1147796

In addition we have a recent report from the United Kingdom Marine Climate Change Impacts Partnership (MCCIP) lead author G.D. McCarthy Atlantic Meridional Overturning Circulation (AMOC) 2017.

12-hourly, 10-day low pass filtered transport timeseries from April 2nd 2004 to February 2017.

Figure 1: Ten-day (colours) and three month (black) low-pass filtered timeseries of Florida Straits transport (blue), Ekman transport (green), upper mid-ocean transport (magenta), and overturning transport (red) for the period 2nd April 2004 to end- February 2017. Florida Straits transport is based on electromagnetic cable measurements; Ekman transport is based on ERA winds. The upper mid-ocean transport, based on the RAPID mooring data, is the vertical integral of the transport per unit depth down to the deepest northward velocity (~1100 m) on each day. Overturning transport is then the sum of the Florida Straits, Ekman, and upper mid-ocean transports and represents the maximum northward transport of upper-layer waters on each day. Positive transports correspond to northward flow.

The RAPID/MOCHA/WBTS array (hereinafter referred to as the RAPID array) has revolutionized basin scale oceanography by supplying continuous estimates of the meridional overturning transport (McCarthy et al., 2015), and the associated basin-wide transports of heat (Johns et al., 2011) and freshwater (McDonagh et al., 2015) at 10-day temporal resolution. These estimates have been used in a wide variety of studies characterizing temporal variability of the North Atlantic Ocean, for instance establishing a decline in the AMOC between 2004 and 2013.

Summary from RAPID data analysis

MCCIP reported in 2006 that:

  • a 30% decline in the AMOC has been observed since the early 1990s based on a limited number of observations. There is a lack of certainty and consensus concerning the trend;
  • most climate models anticipate some reduction in strength of the AMOC over the 21st century due to increased freshwater influence in high latitudes. The IPCC project a slowdown in the overturning circulation rather than a dramatic collapse.And in 2017 that:
  • a substantial increase in the observations available to estimate the strength of the AMOC indicate, with greater certainty, a decline since the mid 2000s;
  • the AMOC is still expected to decline throughout the 21st century in response to a changing climate. If and when a collapse in the AMOC is possible is still open to debate, but it is not thought likely to happen this century.

And also that:

  • a high level of variability in the AMOC strength has been observed, and short term fluctuations have had unexpected impacts, including severe winters and abrupt sea-level rise;
  • recent changes in the AMOC may be driving the cooling of Atlantic ocean surface waters which could lead to drier summers in the UK.

Conclusions

  • The AMOC is key to maintaining the mild climate of the UK and Europe.
  • The AMOC is predicted to decline in the 21st century in response to a changing climate.
  • Past abrupt changes in the AMOC have had dramatic climate consequences.
  • There is growing evidence that the AMOC has been declining for at least a decade, pushing the Atlantic Multidecadal Variability into a cool phase.
  • Short term fluctuations in the AMOC have proved to have unexpected impacts, including being linked
    with severe winters and abrupt sea-level rise.

Background:

Oceans Make Climate: SST, SSS and Precipitation Linked

Climate Pacemaker: The AMOC

Evidence is Mounting: Oceans Make Climate

Mann-made Global Cooling

 

 

Our Goldilocks Climate

haze_archean_2_cropped_2In the fairy tale, Goldilocks entered the three bears’ house to find one bowl of soup too hot, another too cold, and one just right for her to eat. A new study of our planetary history suggests that since its beginning our climate has been self-regulating to avoid extremes, with much less variability in temperature and oceanic pH than previously thought.

An overview of the finding comes from an article in Phys.org and is followed by excerpts from the paper itself published in PNAS.

Introductory Comments from Phys.org article Earth’s stable temperature past suggests other planets could also sustain life  April 2, 2018, University of Washington. Excerpts with my bolds.

Theories about the early days of our planet’s history vary wildly. Some studies have painted the picture of a snowball Earth, when much of its surface was frozen. Other theories have included periods that would be inhospitably hot for most current lifeforms to survive.

New research from the University of Washington suggests a milder youth for our planet. An analysis of temperature through early Earth’s history, published the week of April 2 in the Proceedings of the National Academy of Sciences, supports more moderate average temperatures throughout the billions of years when life slowly emerged on Earth.

“Our results show that Earth has had a moderate temperature through virtually all of its history, and that is attributable to weathering feedbacks—they do a good job at maintaining a habitable climate,” said first author Joshua Krissansen-Totton, a UW doctoral student in Earth and space sciences.

To create their estimate, the researchers took the most recent understanding for how rocks, oceans, and air temperature interact, and put that into a computer simulation of Earth’s temperature over the past 4 billion years. Their calculations included the most recent information for how seafloor weathering occurs on geologic timescales, and under different conditions.

Seafloor weathering was more important for regulating temperature of the early Earth because there was less continental landmass at that time, the Earth’s interior was even hotter, and the seafloor crust was spreading faster, so that was providing more crust to be weathered,” Krissansen-Totton said.

The paper is by Joshua Krissansen-Totton el al., Constraining the climate and ocean pH of the early Earth with a geological carbon cycle model PNAS (2018). Excerpts with my bolds.

The existence of a negative feedback to balance the carbon cycle on million-year timescales is undisputed. Without it, atmospheric CO2 would be depleted, leading to a runaway icehouse, or would accumulate to excessive levels (34). However, the relative importance of continental and seafloor weathering in providing this negative feedback, and the overall effectiveness of these climate-stabilizing and pH-buffering feedbacks on the early Earth are unknown.

In this study, we apply a geological carbon cycle model with ocean chemistry to the entirety of Earth history. The inclusion of ocean carbon chemistry enables us to model the evolution of ocean pH and realistically capture the pH-dependent and temperature-dependent kinetics of seafloor weathering. This is a significant improvement on previous geological carbon cycle models (e.g., refs. 12 and 35) that omit ocean chemistry and instead adopt an arbitrary power-law dependence on pCO2 for seafloor weathering which, as we show, overestimates CO2 drawdown on the early Earth. By coupling seafloor weathering to Earth’s climate and the geological carbon cycle, we calculate self-consistent histories of Earth’s climate and pH evolution, and evaluate the relative importance of continental and seafloor weathering through time. The pH evolution we calculate is therefore more robust than that of Halevy and Bachan (29) because, unlike their model, we do not prescribe pCO2 and temperature histories.

The climate and ocean pH of the early Earth are important for understanding the origin and early evolution of life. However, estimates of early climate range from below freezing to over 70 °C, and ocean pH estimates span from strongly acidic to alkaline. To better constrain environmental conditions, we applied a self-consistent geological carbon cycle model to the last 4 billion years. The model predicts a temperate (0–50 °C) climate and circumneutral ocean pH throughout the Precambrian due to stabilizing feedbacks from continental and seafloor weathering. These environmental conditions under which life emerged and diversified were akin to the modern Earth. Similar stabilizing feedbacks on climate and ocean pH may operate on earthlike exoplanets, implying life elsewhere could emerge in comparable environments.

Schematic of carbon cycle model used in this study. Carbon fluxes (Tmol C y−1) are denoted by solid green arrows, and alkalinity fluxes (Tmol eq y−1) are denoted by red dashed arrows. The fluxes into/out of the atmosphere–ocean system are outgassing, Fout, silicate weathering, Fsil, carbonate weathering, Fcarb, and marine carbonate precipitation, Pocean. The fluxes into/out of the pore space are basalt dissolution, Fdiss, and pore-space carbonate precipitation, Ppore. Alkalinity fluxes are multiplied by 2 because the uptake or release of one mole of carbon as carbonate is balanced by a cation with a 2+ charge (typically Ca2+). A constant mixing flux, J (kg y−1), exchanges carbon and alkalinity between the atmosphere–ocean system and pore space.

The dissolution of basalt in the seafloor is dependent on the spreading rate, pore-space pH, and pore-space temperature (SI Appendix A). This formulation is based on the validated parameterization in ref. 36. Pore-space temperatures are a function of climate and geothermal heat flow. Empirical data and fully coupled global climate models reveal a linear relationship between deep ocean temperature and surface climate (36). Equations relating pore-space temperature, deep ocean temperature, and sediment thickness are provided in SI Appendix A.

Carbon leaves the atmosphere–ocean system through carbonate precipitation in the ocean and pore space of the oceanic crust. At each time step, the carbon abundances and alkalinities are used to calculate the carbon speciation, atmospheric pCO2, and saturation state assuming chemical equilibrium. Saturation states are then used to calculate carbonate precipitation fluxes (SI Appendix A). We allow calcium (Ca) abundance to evolve with alkalinity, effectively assuming no processes are affecting Ca abundances other than carbonate and silicate weathering, seafloor dissolution, and carbonate precipitation. The consequences of this simplification are explored in the sensitivity analysis in SI Appendix C. We do not track organic carbon burial because organic burial only constitutes 10–30% of total carbon burial for the vast majority of Earth history (40), and so the inorganic carbon cycle is the primary control.

We conclude that current best knowledge of Earth’s geologic carbon cycle precludes a hot Archean. Our results are insensitive to assumptions about ocean chemistry, internal evolution, and weathering parameterizations, so a hot early Earth would require some fundamental error in current understanding of the carbon cycle. Increasing the biotic enhancement of weathering by several orders of magnitude as proposed by Schwartzman (60) does not produce a hot Archean because this is mathematically equivalent to zeroing out the continental weathering flux (Fig. 4). In this case the temperature-dependent seafloor weathering feedback buffers the climate of the Earth to moderate temperatures (SI Appendix, Fig. S14). Dramatic temperature increases (or decreases) due to albedo changes also do not change our conclusions due to the buffering effect of the carbon cycle (see above). If both continental and seafloor weathering become supply limited (e.g., refs. 49 and 61), then temperatures could easily exceed 50 °C. However, in this case the carbon cycle would be out of balance, leading to excessive pCO2 accumulation within a few hundred million years unless buffered by some other, unknown feedback.

The only way to produce Archean climates below 0 °C in our model is to assume the Archean outgassing flux was 1–5× lower than the modern flux (SI Appendix, Fig. S12). However, dramatically lowered Archean outgassing fluxes contradict known outgassing proxies and probably require both a stagnant lid tectonic regime and a mantle more reduced than zircon data suggest, which lowers the portion of outgassed CO2 (SI Appendix C). Moreover, even when outgassing is low, frozen climates are not guaranteed (SI Appendix, Fig. S12).

We observe that modeled temperatures are relatively constant throughout Earth history, with Archean temperatures ranging from 271 to 314 K. The combination of continental and seafloor weathering efficiently buffers climate against changes in luminosity, outgassing, and biological evolution. This temperature history is broadly consistent with glacial constraints and recent isotope proxies (Fig. 3D). The continental weathering buffer dominates over the seafloor weathering buffer for most of Earth history, but in the Archean the two carbon sinks are comparable (SI Appendix, Fig. S1). Indeed, if seafloor weathering were artificially held constant, then continental weathering alone may be unable to efficiently buffer the climate of the early Earth—the temperature distribution at 4.0 Ga extends to 370 K, and the atmospheric pCO2 distribution extends to 7 bar (SI Appendix, Fig. S3).

In our nominal model, the median Archean surface temperature is slightly higher than modern surface temperatures. If solar evolution were the only driver of the carbon cycle, then Archean temperatures would necessarily be cooler than modern temperatures; weathering feedbacks can mitigate this cooling but not produce warming. Warmer Archean climates are possible because elevated internal heat flow, lower continental land fraction, and lessened biological enhancement of weathering all act to warm to Precambrian climate. These three factors produce a comparable warming effect (SI Appendix, Fig. S17A and Appendix C), although the magnitude of each is highly uncertain and so temperate Archean temperatures cannot be uniquely attributed to any one variable.

Conclusions

The early Earth was probably temperate. Continental and seafloor weathering buffer Archean surface temperatures to 0–50 °C. This result holds for a broad range of assumptions about the evolution of internal heat flow, crustal production, spreading rates, and the biotic enhancement of continental weathering. Even in extreme scenarios with negligible subaerial Archean land and high methane abundances, a hot Archean (>50 °C) is unlikely. Sub-0 °C climates are also unlikely unless the Archean outgassing flux was unrealistically lower than the modern flux.

The seafloor weathering feedback is important, but less dominant than previously assumed. Consequently, the early Earth would not have been in a snowball state due to pCO2 drawdown from seafloor weathering. In principle, little to no methane is required to maintain a habitable surface climate, although methane should be expected in the anoxic Archean atmosphere once methanogenesis evolved (ref. 62, chap. 11).

Ignoring transient excursions, the pH of Earth’s ocean has evolved monotonically from 6.6+0.6−0.4 at 4.0 Ga (2σ) to 7.0+0.7−0.5 at 2.5 Ga (2σ), and 8.2 in the modern ocean. This evolution is robust to assumptions about ocean chemistry, internal heat flow, and other carbon cycle parameterizations. Consequently, similar feedbacks may control ocean pH and climate on other Earthlike planets with basaltic seafloors and silicate continents, suggesting that life elsewhere could emerge in comparable environments to those on our early planet.

Ocean Temps Falling Feb. 2018

globpop_countries

The best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

  • The ocean covers 71% of the globe and drives average temperatures;
  • SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
  • A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through February 2018.
Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back below its beginning level. Secondly, the Northern Hemisphere added three bumps on the shoulders of Tropical warming, with peaks in August of each year. Also, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.

A global cooling pattern has persisted, seen clearly in the Tropics since its peak in 2016, joined by NH and SH dropping since last August. An upward bump occurred last October, and again in January 2018.  Now the cooling has resumed in February with only the NH showing a slight increase.  As will be shown in the analysis below, 0.4C has been the average global anomaly since 1995 and this month remains lower at 0.349C.  SH erased the January bump while the tropics reached a new low of 0.155 for this period.

Global and NH SSTs are the lowest since 3/2014, while SH and Tropics SSTs are the lowest since 3/2012.

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

Open image in new tab for sharper detail.

1995 is a reasonable starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16, with July 2017 only slightly lower.  Note also that starting in 2014 SH plays a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years as shown by this graph:

The data is annual averages of absolute SSTs measured in the North Atlantic.  The significance of the pulses for weather forecasting is discussed in AMO: Atlantic Climate Pulse

But the peaks coming nearly every July in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.Now the regime shift appears clearly. Starting with 2003, seven times the August average has exceeded 23.6C, a level that prior to ’98 registered only once before, in 1937.  And other recent years were all greater than 23.4C.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up?

To paraphrase the wheel of fortune carnival barker:  “Down and down she goes, where she stops nobody knows.”

Postscript:

In the most recent GWPF 2017 State of the Climate report, Dr. Humlum made this observation:

“It is instructive to consider the variation of the annual change rate of atmospheric CO2 together with the annual change rates for the global air temperature and global sea surface temperature (Figure 16). All three change rates clearly vary in concert, but with sea surface temperature rates leading the global temperature rates by a few months and atmospheric CO2 rates lagging 11–12 months behind the sea surface temperature rates.”

Footnote: Why Rely on HadSST3

HadSST3 is distinguished from other SST products because HadCRU (Hadley Climatic Research Unit) does not engage in SST interpolation, i.e. infilling estimated anomalies into grid cells lacking sufficient sampling in a given month. From reading the documentation and from queries to Met Office, this is their procedure.

HadSST3 imports data from gridcells containing ocean, excluding land cells. From past records, they have calculated daily and monthly average readings for each grid cell for the period 1961 to 1990. Those temperatures form the baseline from which anomalies are calculated.

In a given month, each gridcell with sufficient sampling is averaged for the month and then the baseline value for that cell and that month is subtracted, resulting in the monthly anomaly for that cell. All cells with monthly anomalies are averaged to produce global, hemispheric and tropical anomalies for the month, based on the cells in those locations. For example, Tropics averages include ocean grid cells lying between latitudes 20N and 20S.

Gridcells lacking sufficient sampling that month are left out of the averaging, and the uncertainty from such missing data is estimated. IMO that is more reasonable than inventing data to infill. And it seems that the Global Drifter Array displayed in the top image is providing more uniform coverage of the oceans than in the past.

uss-pearl-harbor-deploys-global-drifter-buoys-in-pacific-ocean

USS Pearl Harbor deploys Global Drifter Buoys in Pacific Ocean

 

2018 Oceans Remain Cool

The best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

  • The ocean covers 71% of the globe and drives average temperatures;
  • SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
  • A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through January 2018.
Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back below its beginning level. Secondly, the Northern Hemisphere added three bumps on the shoulders of Tropical warming, with peaks in August of each year. Also, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.

A global cooling pattern has persisted, seen clearly in the Tropics since its peak in 2016, joined by NH and SH dropping since last August. An upward bump occurred in October, and now again in January 2018.  As will be shown in the analysis below, 0.410C has been the average global anomaly since 1995 and last month remains lower at 0.376C.  SH rose along with the Tropics, while NH held steady.  Global and NH SSTs are the lowest since 3/2014, while Tropics SSTs are the lowest since 3/2012. SH is the lowest January since 2014.

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

Open image in new tab for sharper detail.

1995 is a reasonable starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16, with July 2017 only slightly lower.  Note also that starting in 2014 SH plays a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years as shown by this graph:

The data is annual averages of absolute SSTs measured in the North Atlantic.  The significance of the pulses for weather forecasting is discussed in AMO: Atlantic Climate Pulse

But the peaks coming nearly every July in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.Now the regime shift appears clearly. Starting with 2003, seven times the August average has exceeded 23.6C, a level that prior to ’98 registered only once before, in 1937.  And other recent years were all greater than 23.4C.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up?

Footnote: Why Rely on HadSST3

HadSST3 is distinguished from other SST products because HadCRU (Hadley Climatic Research Unit) does not engage in SST interpolation, i.e. infilling estimated anomalies into grid cells lacking sufficient sampling in a given month. From reading the documentation and from queries to Met Office, this is their procedure.

HadSST3 imports data from gridcells containing ocean, excluding land cells. From past records, they have calculated daily and monthly average readings for each grid cell for the period 1961 to 1990. Those temperatures form the baseline from which anomalies are calculated.

In a given month, each gridcell with sufficient sampling is averaged for the month and then the baseline value for that cell and that month is subtracted, resulting in the monthly anomaly for that cell. All cells with monthly anomalies are averaged to produce global, hemispheric and tropical anomalies for the month, based on the cells in those locations. For example, Tropics averages include ocean grid cells lying between latitudes 20N and 20S.

Gridcells lacking sufficient sampling that month are left out of the averaging, and the uncertainty from such missing data is estimated. IMO that is more reasonable than inventing data to infill. And it seems that the Global Drifter Array displayed in the top image is providing more uniform coverage of the oceans than in the past.

uss-pearl-harbor-deploys-global-drifter-buoys-in-pacific-ocean

USS Pearl Harbor deploys Global Drifter Buoys in Pacific Ocean

 

AMOC Update: Not Showing Climate Threat

The RAPID moorings being deployed. Credit: National Oceanography Centre.

The AMOC is back in the news following a recent Ocean Sciences meeting.  This update adds to the theme Oceans Make Climate. Background links are at the end, including one where chief alarmist M. Mann claims fossil fuel use will stop the ocean conveyor belt and bring a new ice age.  Actual scientists are working away methodically on this part of the climate system, and are more level-headed.  H/T GWPF for noticing the recent article in Science Ocean array alters view of Atlantic ‘conveyor belt’  By Katherine Kornei Feb. 17, 2018 . Excerpts with my bolds.

The powerful currents in the Atlantic, formally known as the Atlantic meridional overturning circulation (AMOC), are a major engine in Earth’s climate. The AMOC’s shallower limbs—which include the Gulf Stream—transport warm water from the tropics northward, warming Western Europe. In the north, the waters cool and sink, forming deeper limbs that transport the cold water back south—and sequester anthropogenic carbon in the process. This overturning is why the AMOC is sometimes called the Atlantic conveyor belt.

Fig. 1. Schematic of the major warm (red to yellow) and cold (blue to purple) water pathways in the NASPG (North Atlantic subpolar gyre ) credit: H. Furey, Woods Hole Oceanographic Institution): Denmark Strait (DS), Faroe Bank Channel (FBC), East and West Greenland Currents (EGC and WGC, respectively), NAC, DSO, and ISO.

Last week, at the American Geophysical Union’s (AGU’s) Ocean Sciences meeting here, scientists presented the first data from an array of instruments moored in the subpolar North Atlantic. The observations reveal unexpected eddies and strong variability in the AMOC currents. They also show that the currents east of Greenland contribute the most to the total AMOC flow. Climate models, on the other hand, have emphasized the currents west of Greenland in the Labrador Sea. “We’re showing the shortcomings of climate models,” says Susan Lozier, a physical oceanographer at Duke University in Durham, North Carolina, who leads the $35-million, seven-nation project known as the Overturning in the Subpolar North Atlantic Program (OSNAP).

Fig. 2. Schematic of the OSNAP array. The vertical black lines denote the OSNAP moorings with the red dots denoting instrumentation at depth. The thin gray lines indicate the glider survey. The red arrows show pathways for the warm and salty waters of subtropical origin; the light blue arrows show the pathways for the fresh and cold surface waters of polar origin; and the dark blue arrows show the pathways at depth for waters that originate in the high-latitude North Atlantic and Arctic.

The research and analysis is presented by Dr. Lozier et al. in this publication Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System Images above and text excerpted below with my bolds.

For decades oceanographers have assumed the AMOC to be highly susceptible to changes in the production of deep waters at high latitudes in the North Atlantic. A new ocean observing system is now in place that will test that assumption. Early results from the OSNAP observational program reveal the complexity of the velocity field across the section and the dramatic increase in convective activity during the 2014/15 winter. Early results from the gliders that survey the eastern portion of the OSNAP line have illustrated the importance of these measurements for estimating meridional heat fluxes and for studying the evolution of Subpolar Mode Waters. Finally, numerical modeling data have been used to demonstrate the efficacy of a proxy AMOC measure based on a broader set of observational data, and an adjoint modeling approach has shown that measurements in the OSNAP region will aid our mechanistic understanding of the low-frequency variability of the AMOC in the subtropical North Atlantic.

Fig. 7. (a) Winter [Dec–Mar (DJFM)] mean NAO index. Time series of temperature from the (b) K1 and (c) K9 moorings.

Finally, we note that while a primary motivation for studying AMOC variability comes from its potential impact on the climate system, as mentioned above, additional motivation for the measure of the heat, mass, and freshwater fluxes in the subpolar North Atlantic arises from their potential impact on marine biogeochemistry and the cryosphere. Thus, we hope that this observing system can serve the interests of the broader climate community.

Fig. 10. Linear sensitivity of the AMOC at (d),(e) 25°N and (b),(c) 50°N in Jan to surface heat flux anomalies per unit area. Positive sensitivity indicates that ocean cooling leads to an increased AMOC—e.g., in the upper panels, a unit increase in heat flux out of the ocean at a given location will change the AMOC at (d) 25°N or (e) 50°N 3 yr later by the amount shown in the color bar. The contour intervals are logarithmic. (a) The time series show linear sensitivity of the AMOC at 25°N (blue) and 50°N (green) to heat fluxes integrated over the subpolar gyre (black box with surface area of ∼6.7 × 10 m2) as a function of forcing lead time. The reader is referred to Pillar et al. (2016) for model details and to Heimbach et al. (2011) and Pillar et al. (2016) for a full description of the methodology and discussion relating to the dynamical interpretation of the sensitivity distributions.

In summary, while modeling studies have suggested a linkage between deep-water mass formation and AMOC variability, observations to date have been spatially or temporally compromised and therefore insufficient either to support or to rule out this connection.

Current observational efforts to assess AMOC variability in the North Atlantic.

The U.K.–U.S. Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) program at 26°N successfully measures the AMOC in the subtropical North Atlantic via a transbasin observing system (Cunningham et al. 2007; Kanzow et al. 2007; McCarthy et al. 2015). While this array has fundamentally altered the community’s view of the AMOC, modeling studies over the past few years have suggested that AMOC fluctuations on interannual time scales are coherent only over limited meridional distances. In particular, a break point in coherence may occur at the subpolar–subtropical gyre boundary in the North Atlantic (Bingham et al. 2007; Baehr et al. 2009). Furthermore, a recent modeling study has suggested that the low-frequency variability of the RAPID–MOCHA appears to be an integrated response to buoyancy forcing over the subpolar gyre (Pillar et al. 2016). Thus, a measure of the overturning in the subpolar basin contemporaneous with a measure of the buoyancy forcing in that basin likely offers the best possibility of understanding the mechanisms that underpin AMOC variability. Finally, though it might be expected that the plethora of measurements from the North Atlantic would be sufficient to constrain a measure of the AMOC within the context of an ocean general circulation model, recent studies (Cunningham and Marsh 2010; Karspeck et al. 2015) reveal that there is currently no consensus on the strength or variability of the AMOC in assimilation/reanalysis products.

Atlantic Meridional Overturning Circulation (AMOC). Red colours indicate warm, shallow currents and blue colours indicate cold, deep return flows. Modified from Church, 2007, A change in circulation? Science, 317(5840), 908–909. doi:10.1126/science.1147796

In addition we have a recent report from the United Kingdom Marine Climate Change Impacts Partnership (MCCIP) lead author G.D. McCarthy Atlantic Meridional Overturning Circulation (AMOC) 2017.

12-hourly, 10-day low pass filtered transport timeseries from April 2nd 2004 to February 2017.

Figure 1: Ten-day (colours) and three month (black) low-pass filtered timeseries of Florida Straits transport (blue), Ekman transport (green), upper mid-ocean transport (magenta), and overturning transport (red) for the period 2nd April 2004 to end- February 2017. Florida Straits transport is based on electromagnetic cable measurements; Ekman transport is based on ERA winds. The upper mid-ocean transport, based on the RAPID mooring data, is the vertical integral of the transport per unit depth down to the deepest northward velocity (~1100 m) on each day. Overturning transport is then the sum of the Florida Straits, Ekman, and upper mid-ocean transports and represents the maximum northward transport of upper-layer waters on each day. Positive transports correspond to northward flow.

The RAPID/MOCHA/WBTS array (hereinafter referred to as the RAPID array) has revolutionized basin scale oceanography by supplying continuous estimates of the meridional overturning transport (McCarthy et al., 2015), and the associated basin-wide transports of heat (Johns et al., 2011) and freshwater (McDonagh et al., 2015) at 10-day temporal resolution. These estimates have been used in a wide variety of studies characterizing temporal variability of the North Atlantic Ocean, for instance establishing a decline in the AMOC between 2004 and 2013.

Summary from RAPID data analysis

MCCIP reported in 2006 that:

  • a 30% decline in the AMOC has been observed since the early 1990s based on a limited number of observations. There is a lack of certainty and consensus concerning the trend;
  • most climate models anticipate some reduction in strength of the AMOC over the 21st century due to increased freshwater influence in high latitudes. The IPCC project a slowdown in the overturning circulation rather than a dramatic collapse.And in 2017 that:
  • a substantial increase in the observations available to estimate the strength of the AMOC indicate, with greater certainty, a decline since the mid 2000s;
  • the AMOC is still expected to decline throughout the 21st century in response to a changing climate. If and when a collapse in the AMOC is possible is still open to debate, but it is not thought likely to happen this century.

And also that:

  • a high level of variability in the AMOC strength has been observed, and short term fluctuations have had unexpected impacts, including severe winters and abrupt sea-level rise;
  • recent changes in the AMOC may be driving the cooling of Atlantic ocean surface waters which could lead to drier summers in the UK.

Conclusions

  • The AMOC is key to maintaining the mild climate of the UK and Europe.
  • The AMOC is predicted to decline in the 21st century in response to a changing climate.
  • Past abrupt changes in the AMOC have had dramatic climate consequences.
  • There is growing evidence that the AMOC has been declining for at least a decade, pushing the Atlantic Multidecadal Variability into a cool phase.
  • Short term fluctuations in the AMOC have proved to have unexpected impacts, including being linked
    with severe winters and abrupt sea-level rise.

Background:

Climate Pacemaker: The AMOC

Evidence is Mounting: Oceans Make Climate

Mann-made Global Cooling

 

 

Oceans Make Climate: SST, SSS and Precipitation Linked

Satellite image of sea surface temperature in the Gulf Stream.

Climates are locally defined according to their weather patterns combining temperature and precipitation. Those two variables determine the flora and fauna to survive and flourish in any locale. A number of posts here support the theme that Oceans Govern Climate, and this is another one, summarizing the findings from a new paper published in Nature Communications Pronounced centennial-scale Atlantic Ocean climate variability correlated with Western Hemisphere hydroclimate by Thirumalai et al. 2018. Below is an overview from Science Daily followed by excerpts from the paper with my bolds. (Note:  SST refers to sea surface temperatures, SSS refers to sea surface salinity, and GOM means Gulf of Mexico.)

Science Daily Rainfall and ocean circulation linked in past and present

Research conducted at The University of Texas at Austin has found that changes in ocean currents in the Atlantic Ocean influence rainfall in the Western Hemisphere, and that these two systems have been linked for thousands of years.

The findings, published on Jan. 26 in Nature Communications, are important because the detailed look into Earth’s past climate and the factors that influenced it could help scientists understand how these same factors may influence our climate today and in the future.

“The mechanisms that seem to be driving this correlation [in the past] are the same that are at play in modern data as well,” said lead author Kaustubh Thirumalai, postdoctoral researcher at Brown University who conducted the research while earning his Ph.D. at the UT Austin Jackson School of Geosciences. “The Atlantic Ocean surface circulation, and however that changes, has implications for how the rainfall changes on continents.”

Open image in new tab if animation is not working.

Thirumalai et al. 2018 Abstract:

Surface-ocean circulation in the northern Atlantic Ocean influences Northern Hemisphere climate. Century-scale circulation variability in the Atlantic Ocean, however, is poorly constrained due to insufficiently-resolved paleoceanographic records.

Here we present a replicated reconstruction of sea-surface temperature and salinity from a site sensitive to North Atlantic circulation in the Gulf of Mexico which reveals pronounced centennial-scale variability over the late Holocene. We find significant correlations on these timescales between salinity changes in the Atlantic, a diagnostic parameter of circulation, and widespread precipitation anomalies using three approaches: multiproxy synthesis, observational datasets, and a transient simulation.

Our results demonstrate links between centennial changes in northern Atlantic surface-circulation and hydroclimate changes in the adjacent continents over the late Holocene. Notably, our findings reveal that weakened surface-circulation in the Atlantic Ocean was concomitant with well-documented rainfall anomalies in the Western Hemisphere during the Little Ice Age.

Here we address this shortfall and reconstruct SST and SSS variability over the last 4,400 years using foraminiferal geochemistry in marine sediments cored from the Garrison Basin (26°40.19′N,93°55.22′W, (purple circle in diagrams above), northern GOM. We make inferences about past changes in Loop Current strength by identifying time periods in our reconstruction where synchronous decreases in SST and SSS are interpreted as periods with a weaker Loop Current due to reduced eddy penetration over that period and vice versa. Thus, we assess the spatial heterogeneity of the putative reduction of Atlantic surface-ocean circulation and furthermore, with multiproxy synthesis, correlation analysis, and model-data comparison, we document linkages between changes in Atlantic surface-circulation and Western Hemisphere hydroclimate anomalies. Our findings reveal that regardless of whether changes in the AMOC and deepwater formation occurred or not, weakened surface-circulation prevailed in the northern Atlantic basin during the Little Ice Age and was concomitant with widespread and well-documented precipitation anomalies over the adjacent continents.

Figure 2. Garrison Basin multicore reconstructions and corresponding stacked records. Individual core Mg/Ca (mmol/mol) and δ18Oc data (‰, VPDB), and δ18Osw (‰, VSMOW) and SST (°C) reconstructions (blue–MCA, red- MCB, yellow–MCC) plotted with median and 68% uncertainty envelope incorporating age, analytical, calibration, and sampling errors (a-d) along with corresponding median stacked records with 68% and 95% confidence bounds (e-h). Diamonds in a and e indicate stratigraphic points sampled for radiocarbon. Gray histogram in g is the probability distribution for a changepoint in the δ18Osw time series. Orange circle in g is the mean of available δ18Osw measurements in the GOM and orange line in h is observed monthly mean SST with uncertainty envelope calculated using a Monte Carlo procedure that simulates foraminiferal sampling protocol. Purple line in h is the 100-year running correlation between SST and δ18Osw with corresponding uncertainty with shaded boxes indicating correlations with r > 0.7 (p < 0.001), which is the basis for identifying time periods where Loop Current and associated processes are relevant.

Loop Current control on regional SST and SSS variability

We analyzed long-term (~multidecadal) observations in instrumental datasets to place our reconstructions into a global climatic context. The HadISST data set22 documents 0.4–0.7 °C of multidecadal SST variability in the northern GOM over the last century. On these multidecadal timescales, SSTs in the northern GOM correlate highly with SST in the Loop Current region. In particular, long-term SST variability here is impacted by the Loop Current through its eddy shedding processes which are coupled to the strength of transport from the Yucatan Straits through the Florida Straits: if Loop Current transport is anomalously low, then northern GOM SSTs are anomalously cooler due to decreased eddy penetration and the opposite is the case when Loop Current transport is anomalously higher, i.e., northern GOM experiences anomalously warmer conditions. Furthermore, the Loop Current, sitting upstream of where the Gulf Stream originates, correlates highly with SST associated with regions encompassing downstream currents.

In summary, correlation analysis using SSS datasets provides a blueprint for investigating circulation variability and transport into the North Atlantic Ocean.

We also examine long-term correlations between SSS in the northern GOM and mean annual rainfall in the continents adjacent to the Atlantic Basin using rain-gauge precipitation datasets (Fig. 1). Most notably, GOM SSS is anticorrelated with southern North American rainfall (i.e., fresher GOM with wetter southern North America) and is positively correlated with rainfall in West Africa, northern South America, and the southeast United States (|r| > 0.6, p < 0.01). These inferences demonstrate a correspondence between Western Hemisphere hydroclimate and Atlantic Ocean circulation on multidecadal timescales.

Approach to understanding past circulation and hydroclimate

Taken together, we interpret past periods in the Garrison Basin reconstructions when both SST and δ18Osw variability were positively correlated (salty/warm or fresh/cool) as periods during which Loop Current strength fluctuated. We hypothesize that during these periods, increased Loop Current penetration led to increased SST as well as increased advection of more enriched δ18Osw (or more saline waters) into the northern GOM. Using the correlation analysis as a blueprint28, we can pinpoint whether these past fluctuations in the northern GOM δ18Osw record (such as during the LIA) were concomitant with changes in pan-Atlantic SSS records that would implicate circulation changes in the northern Atlantic Ocean. Finally, the long-term correlations with precipitation allow us to contextualize periods where surface-ocean circulation and continental rainfall anomalies were linked, which can then be placed within a multiproxy framework.

In comparing available reconstructions of precipitation during the LIA with our correlation map (Fig. 1), we find remarkable agreement with the proxy record: tree-ring-based PDSI reconstructions in southern North America, and stalagmites from southern Mexico43 and Peru44 capture a wetter LIA compared to modern times whereas a lake record from southern Ghana, titanium percent in Cariaco Basin sediments, and reconstructed PDSI in the southeast U. S. indicate dry LIA conditions. Additional proxy records appear to corroborate this observation as well (brown and green squares in Fig. 1; Supplementary Table 1). These mean state changes during the LIA all appear to be coeval with an anomalously fresher northern Atlantic Ocean, indicative of weakened Gulf Stream strength and reduced surface-ocean circulation.

Figure 5. Simulated correlations between sea-surface salinity and rainfall over last millennium. Correlation map between northern Gulf of Mexico SSS (dashed red box) and global oceanic SSS (red-blue scale) as well as continental precipitation (brown-green scale) from the MPI-ESM transient simulation of the last millennium along with locations of proxy records used in the study. Proxy markers are filled as in Fig. 1. Correlations were performed with 50–150 year bandpass filters to isolate centennial scale variability, where black stippling indicates significance at the 5% confidence level

The transient simulation indicates that a weaker gyre, increased sea-ice cover, and reduced interhemispheric heat transport causes the ITCZ to shift southward and produces anomalous rainfall over the Americas.

This state of weakened AMOC, observed in millennial-scale and glacial paleo-studies, with cool and fresh north Atlantic anomalies and a southward ITCZ, can induce increased rainfall over the southwest US via atmospheric teleconnections associated with the North Atlantic subtropical high overlying the gyre. Despite this southward shift, positive SSS anomalies can occur in the tropical Atlantic (and negative anomalies in the northern Atlantic) due to reduced freshwater input resulting from decreased rainfall in the Amazon and West African regions. Eventually, the tropical positive salinity anomaly in the southern Atlantic propagates northward, thereby strengthening meridional oceanic transport and providing the delayed negative feedback.

Though the length of the instrumental record limits us from directly analyzing centennial-scale correlations, there is theoretical and modeling evidence to implicate similar ocean-atmosphere processes on multidecadal and centennial timescales. Both model and observational analyses reveal a dipolar structure in Atlantic Ocean SSS that is consistent with the LIA proxies and thereby supports our hypothesis linking meridional salt transport and tropical rainfall. Both analyses also display similarities in continental precipitation patterns over western Africa, northern South America, and the southwestern United States, which are also consistent with the LIA hydroclimate proxies.

Summary

The broad agreement between the analyses supports similar ocean-atmosphere processes on multidecadal-to-centennial timescales, and provides additional evidence of a robust century-scale link between circulation changes in the Atlantic basin and precipitation in the adjacent continents.

Regardless of the specific physical mechanism concerning the onset of the LIA, and whether AMOC changes were linked with circulation changes in the surface ocean, we hypothesize that the reported oscillatory feedback on centennial-time scales involving the surface-circulation in the Atlantic Ocean and Western Hemisphere hydroclimate played an important role in last millennium climate variability and perhaps, over the late Holocene.

 

 

 

 

 

 

 

Oceans Cool Off Previous 3 Years

The best context for understanding these three years comes from the world’s sea surface temperatures (SST), for several reasons:

  • The ocean covers 71% of the globe and drives average temperatures;
  • SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
  • A major El Nino was the dominant climate feature these years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through December 2017.
HadSST122017
After a bump in October the downward temperature trend has strengthened. As will be shown in the analysis below, 0.4C has been the average global anomaly since 1995 and December has now gone lower to 0.325C.  NH dropped  sharply along with the Tropics.  SH held steady erasing the Oct. bump.  All parts of the ocean are clearly lower than at any time in the past 3 years.

For Reference:
Global SSTs are the lowest since 3/2013
NH SSTs are the lowest since 3/3014
SH SSTs are the lowest since 1/2012
Tropics SSTs are the lowest since 3/3012

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

HadSST1995to122017

Open image in new tab for sharper detail.

1995 is a reasonable starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16, with July 2017 only slightly lower.  Note also that starting in 2014 SH plays a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years as shown by this graph:

The data is annual averages of absolute SSTs measured in the North Atlantic.  The significance of the pulses for weather forecasting is discussed in AMO: Atlantic Climate Pulse

But the peaks coming nearly every July in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.Now the regime shift appears clearly. Starting with 2003, seven times the August average has exceeded 23.6C, a level that prior to ’98 registered only once before, in 1937.  And other recent years were all greater than 23.4C.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up?

uss-pearl-harbor-deploys-global-drifter-buoys-in-pacific-ocean

USS Pearl Harbor deploys Global Drifter Buoys in Pacific Ocean

 

Natural Climate Cycles: Fresh Insights

Multiple aspects of nature cycle and interact over various time scales, frustrating attempts to discern human influence upon the climate. To demonstrate the challenge, consider one simple physical example: The compound pendulum shown in operation below:

Recently a comment (H/T tom0mason) alerted me to the science demonstrated by the double compound pendulum, that is, a second pendulum attached to the ball of the first one. It consists entirely of two simple, well understood objects functioning as pendulums, only now each is influenced by the behavior of the other.

Lo and behold, you observe that a double pendulum in motion produces chaotic behavior. In a remarkable achievement, complex equations have been developed that can and do predict the positions of the two balls over time, so in fact the movements are not truly chaotic, but with considerable effort can be determined. The equations and descriptions are at Wikipedia Double Pendulum.

But here is the kicker, as described in tomomason’s comment:

If you arrive to observe the double pendulum at an arbitrary time after the motion has started from an unknown condition (unknown height, initial force, etc) you will be very taxed mathematically to predict where in space the pendulum will move to next, on a second to second basis. Indeed it would take considerable time and many iterative calculations (preferably on a super-computer) to be able to perform this feat. And all this on a very basic system of known elementary mechanics.  More at Climate Chaos

Fresh Study of Antarctic Oscillation

Many of the cycles driving the climate system are circulations with the ocean and air interacting. A 2018 study looks in more detail at one of the more important ones: The Antarctic Oscillation (AAO), also known as Southern Annular Mode (SAM).  The Antarctic Centennial Oscillation: A Natural Paleoclimate Cycle in the Southern Hemisphere That Influences Global Temperature  W. Jackson Davis, Peter J. Taylor and W. Barton Davis, Santa Cruz USA Published: 8 January 2018
H/T Kenneth Richard NoTricksZone.  Excerpts from paper in italics with added images and bolds.

We report a previously-unexplored natural temperature cycle recorded in ice cores from Antarctica—the Antarctic Centennial Oscillation (ACO)—that has oscillated for at least the last 226 millennia. Here we document the properties of the ACO and provide an initial assessment of its role in global climate. We analyzed open-source databases of stable isotopes of oxygen and hydrogen as proxies for paleo-temperatures. We find that centennial-scale spectral peaks from temperature-proxy records at Vostok over the last 10,000 years occur at the same frequencies (±2.4%) in three other paleoclimate records from drill sites distributed widely across the East Antarctic Plateau (EAP), and >98% of individual ACOs evaluated at Vostok match 1:1 with homologous cycles at the other three EAP drill sites and conversely.

Superimposed upon these multi-millennial climate cycles are numerous shorter global and regional climate cycles ranging in period from several millennia down to a few weeks. Included among these faster oscillations are millennial-scale cycles, particularly the Bond cycle and centennial-scale cycles, notably the Antarctic Oscillation (AAO) known also as the Southern Annular Mode (SAM) and tracked quantitatively by means of the Southern Oscillation Index (SOI). These interdependent Southern Hemisphere (SH) temperature-proxy oscillations exhibit both centennial and decadal frequency components. Similar periodicity appears in independent reconstructions of more contemporary temperature proxies from James Ross Island and snow accumulation in stacked records from snowpits at Vostok.
Figure 3. Spectral power density periodogram of temperature-proxy records from Vostok over the Holocene. Arrows and associated numerals designate spectral peaks at the indicated periods in years (y) that are discernible within the indicated confidence limits. Discernible peaks at p < 0.005 are labeled 1–6 for reference to the same peaks portrayed in subsequent figures. The confidence limits are represented by best-fit exponential curves fitted to stepwise forward regression data over the whole frequency spectrum represented in the periodogram (Methods and SM). Fisher’s Kappa and the corresponding probability that the periodogram results from white noise are 17.34 and p < 8.7 × 10−7, respectively.

Periodograms of the remaining three AICC2012 climate records during the Holocene are similar to the periodogram of the Vostok record (Figure 4). All are bounded near the low end by a peak corresponding approximately to the mean period of the TOC350V cycles and near the high end by a peak corresponding to the Bond cycle in the NH and ranging from 825 to 1027 years. Between these extremes lie at least four additional centennial-scale peaks in all AICC2012 climate records evaluated.

Interannually the AAO shifts between phases, designated here as positive and normal (or negative.)

The null hypothesis that TOC350V cycles comprise random variation in cycle structure was tested by means of cyclic autocorrelation coefficients. We find that autocorrelation coefficients alternate between positive and negative at the same periodicity as the corresponding TOC350V cycle frequency (Figure 5). Near peaks and troughs, nearly all of these autocorrelation coefficients are discernibly different from zero at low alpha levels (at least at p < 0.05). These autocorrelation results supplement and extend spectral periodograms to confirm that TOC350V cycles comprise nonrandom periodic sequences. Such positive autocorrelation results would not be possible unless the short time series evaluated represent relatively stationary time series over the time periods evaluated.

Modern measures of AAO showing the positive anomalies compared to slightly negative normally in this time frame.

Discussion and Conclusions
Centennial-scale climate cycles reported previously by several investigators and in this paper are significant in at least three contexts.

First, centennial-scale climate cycles demonstrate “an important role of natural multicentennial variability that is likely to continue”. When both the mean and variance of any centennial-scale climate cycle are known, as is the case for the TOC350V cycles documented here (Table 1), then the future behavior of such cycles can be projected within well-defined confidence limits. Understanding centennial-scale temperature cycles can therefore contribute to precise climate projections over timelines that are most pertinent to human and civilizational life cycles, decades to centuries. This approach to the projection of future climate change has been pioneered by Liu and colleagues based on analysis of tree ring data from the Tibetan Plateau. From past centennial-scale temperature oscillations, they project a steep decline of temperature on the Tibetan Plateau of ~3 °C between 2006 and 2068, followed by a weaker warming trend and continuing on a cyclic basis into the future.

JMA refers to Japan El Nino index. The graph shows that often a peak in one index coincides with a valley in the other one. This suggests a teleconnection between AAO and ENSO cycles.

Second, centennial-scale paleoclimate cycles comprise a “natural” source of temperature forcing, i.e., one that is free from anthropogenic influences. Human impact on global climate from agriculture and land clearing may have begun as early as the mid-Holocene, but earlier climate change was presumably devoid of anthropogenic influences. Characterizing past cycles of temperature fluctuation can therefore help inform the distinction between natural (non-anthropogenic) and anthropogenic forcing of climate in the present, as discussed further below.

Emperor penguins  in Antarctica.

Third, Antarctic temperature fluctuations on several time scales are reflected worldwide and in the NH after a delay of 0.5 to 3.0 millennia. These delays were measured for older time periods, however, generally before the LGT, and may be shorter for more recent climate events in a warmer environment (see below). Given the close association between AIMs (Antarctic Isotope Maxima) in the Antarctic and D-O events in the NH, as demonstrated repeatedly by previous investigators, the discovery here that AIMs are composed of summated TOC350V cycles constitutes strong evidence that ACOs manifest globally. The centennial-scale climate cycles identified in the NH may be northerly manifestations of the Antarctic TOC350V climate cycle documented here, a hypothesis that remains to be tested. In the meantime, the present findings demonstrate that the ACO and its potential modern counterpart (the AAO; see below) influence the temperature of the NH. This finding suggests a potentially-fruitful research direction aimed at assessing the impact of the contemporary AAO on global climate and weather. Our study raises the possibility that the ACO/AAO entrains global temperature and serves as the primary pacemaker of centennial fluctuations in temperature in both hemispheres while simultaneously modulating shorter cycles.