Professional hydrologist Rob Ellison has for years been thinking and writing to connect the dots between the sun, ocean and climate. Recently he wrote this post at his excellent blog Terra et Aqua, An Earnest Discovery of Climate Causality (link in red)
Below I provide some excerpts from his discussion about an ocean mechanism which would be much better understood, were it not for the CO2 obsession sucking up most of the research funding.
It is hypothesized that upwelling in the Pacific Ocean is modulated by solar activity over periods of decades to millennia – with profound impacts on communities and ecosystems globally. The great resonant systems of the Pacific respond at variable periods – the tempo increased last century for instance – of La Niña and El Niño alternation. . .The mechanism proposed is a spinning up of the Pacific gyres as a result of colder and denser polar air. Low solar activity spins up the gyres producing more frequent La Niña (more equatorial upwelling) – and vice versa.
Pacific Oscillations Global Impact
The Pacific has a globally influential role in climate variability at scales of months to millennia. The variability in atmospheric temperature, rainfall and biology has its origin in the volume of cold water rising off California and in the equatorial Pacific. It is an ever changing anomaly.
The principle of atmospheric heating and cooling by ENSO is very simple. Cold, nutrient rich currents cascade through the deep oceans over a millennia or more. These turbulent currents don’t generally emerge through a sun warmed surface layer. By far the most significant deep ocean upwelling is in the eastern and central Pacific. Cold water in contact with the atmosphere absorbs heat and warms as the atmosphere cools. At times there is less upwelling and warm water spreads eastward across the Pacific – warming the atmosphere. It is simple enough to see in temperature data.
I have a preference for near global coverage and depth integrated satellite temperature records – it doesn’t miss energy in latent heat at the surface for one thing. 21st century instrumentation is much to be preferred going forward. Over the past century the 20 to 30 year influence of the Pacific Decadal Oscillation (PDO) anomaly can be seen in the surface records. Warming to the mid 1940’s, cooling to 1976, warming to 1998 and little change since. The PDO and ENSO are, moreover, in lockstep. A cooler PDO anomaly and more frequent and intense La Niña – and vice versa.
Pacific Gyres Spinning Up Climate Change
The atmospheric/ocean system of triggers and feedbacks varies – usually abruptly with triggers. The trigger for more upwelling I can only imagine is the great ocean gyres. Ocean gyres spin up on the surface through winds and planetary rotation. Pressure systems shift polar winds and storms into lower latitudes. High polar atmospheric pressures spin up the gyres pushing cold polar water into the Californian and Peruvian currents. Roiling cold water upwelling sets up wind and current feedback across the Pacific.
More polar cold water at the surface facilitates upwelling in critical regions. Trade winds spin up as a feedback and piles warm water against Australia and Indonesia. Sometimes the winds falter and warm water flows back eastward suppressing cold upwelling. The whole is a complex and dynamic system triggered by changes in atmospheric pressure zones in the north and south Pacific. Great movements of atmospheric mass driven by a marginal change in solar activity. A large reaction from a small jolt as expected with technically chaotic systems.
Tessa Vance and colleagues from the Antarctic Climate and Ecosystems CRC found a proxy of eastern Pacific upwelling in an ice core at the Law Dome Antarctica. A higher salt content – from polar westerlies – is a proxy for solar activity. But also results in changes in the great Pacific gyres and the intensity of upwelling. More upwelling brings rain and cyclones to Indonesia and northern and eastern Australia, drought in the United States of and South America, cooler global temperatures and biological abundance. Less in El Niña conditions and we – in Australia – get drought. The absolute volume of rainfall is roughly constant but where it falls on the planet changes.
The record captures in high resolution the 20 to 30 year Pacific beat, the change in the ENSO tempo last century and has at least a resemblance to the solar signal over a 1000 years. But even with a millennial high El Niño anomaly last century – conditions have been far more extreme at other times in the past 12,000 years.
Will there be more La Niña over the next centuries? Can we expect more El Niño in a thousand years? Might we see great herds return to the Sahel? The future remains unpredictable. Still – a return to the mean scenario does suggest better odds on a cooler sun and a little more upwelling in the Pacific Ocean – a cooling influence on the atmosphere and the inevitable regional variabilities in rainfall.
Oceans Make Climate is a major theme at this blog, since I fortunately made the acquaintance of Dr. Arnd Bernaerts. Rob Ellison adds another important dimension with his consideration of the gyres.
Recently I noticed how sea surface temperatures drove the 2015-2016 global warming, as shown in the HadSST3 record:
Note that higher temps in 2015 and 2016 are first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back to its beginning level. Secondly, the Northern Hemisphere added two bumps on the shoulders of Tropical warming, with peaks in August of each year. Finally, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.
Much ado will be made of this warming, including claims of human causation, despite the obvious oceanic origin. Further, it is curious that CO2 functions as a warming agent so unevenly around the world, and that the Tropics drove this event, contradicting CO2 warming theory.