Every day there are reports like this:
An annual breach of 2 degrees could happen as soon as 2030, according to climate model simulations, although there’s always the chance that climate models are slightly underestimating or overestimating how close we are to that date. Writing with fellow meteorologist Jeff Masters for Weather Underground, Bob Henson said the current spike means “we are now hurtling at a frightening pace toward the globally agreed maximum of 2.0°C warming over pre-industrial levels.”
That abstract, mathematically averaged world, the subject of so much media space and alarm, has almost nothing to do with the world where any of us live. Because nothing on our planet moves in unison.
Start with the hemispheres:
There’s clearly warming over the century, but also a divergence since about 1975, whereby NH rises much more than the SH.
Using round numbers, the Northern Hemisphere (NH) half of the total surface combines 20% land with 30% ocean, while the SH comprises 9% land with 41% ocean. With the oceans having huge heat capacities relative to the land, the NH has much more volatility in temperatures than does the SH. But more importantly, the trends in multi-decadal warming and cooling also differ.
Climates Are Found Down in the Weeds
The top-down global view needs to be supplemented with a bottom-up appreciation of the diversity of climates and their changes.
The ancient Greeks were the first to classify climate zones. From their travels and sea-faring experiences, they called the equatorial regions Torrid, due to the heat and humidity. The mid-latitudes were considered Temperate, including their home Mediterranean Sea. Further North and South, they knew places were Frigid.
Based on empirical observations, Köppen (1900) established a climate classification system which uses monthly temperature and precipitation to define boundaries of different climate types around the world. Since its inception, this system has been further developed (e.g. Köppen and Geiger, 1930; Stern et al., 2000) and widely used by geographers and climatologists around the world.
Köppen and Climate Change
The focus is on differentiating vegetation regimes, which result primarily from variations in temperature and precipitation over the seasons of the year. Now we have an interesting study that considers shifts in Köppen climate zones over time in order to identify changes in climate as practical and local/regional realities.
The paper is: Using the Köppen classiﬁcation to quantify climate variation and change: An example for 1901–2010
By Deliang Chen and Hans Weiteng Chen
Department of Earth Sciences, University of Gothenburg, Sweden
Hans Chen has built an excellent interactive website (here): The purpose of this website is to share information about the Köppen climate classification, and provide data and high-resolution figures from the paper Chen and Chen, 2013: Using the Köppen classification to quantify climate variation and change: An example for 1901–2010 (pdf)
The Köppen climate classiﬁcation consists of ﬁve major groups and a number of sub-types under each major group, as listed in Table 1. While all the major groups except B are determined by temperature only, all the sub-types except the two sub-types under E are decided based on the combined criteria relating to seasonal temperature and precipitation. Therefore, the classiﬁcation scheme as a whole represents different climate regimes of various temperature and precipitation combinations.
Main characteristics of the Köppen climate major groups and sub-types:
|A: Tropical||Tropical rain forest: Af
Tropical monsoon: Am
Tropical wet and dry savanna: Aw, As
|B: Dry||Desert (arid): BWh, BWk
Steppe (semi-arid): BSh, BSk
|C: Mild temperate||Mediterranean: Csa, Csb, Csc
Humid subtropical: Cfa, Cwa
Oceanic: Cfb, Cfc, Cwb, Cwc
|D: Snow||Humid: Dfa, Dwa, Dfb, Dwb, Dsa, Dsb
Subarctic: Dfc, Dwc, Dfd, Dwd, Dsc, Dsd
|E: Polar||Tundra: ET
Ice cap: EF
Temporal Changes in Climate Zones
This study used a global gridded dataset with monthly mean temperature and precipitation, covering 1901–2010, which was produced and documented by Kenji Matsuura and Cort J. Willmott from Department of Geography, University of Delaware. Station data were compiled from different sources, including Global Historical Climatology Network version 2 (GHCN2) and the Global Surface Summary of Day (GSOD).The data and associated documentations can be found at http://climate.geog.udel.edu/climate/html_pages/Global2011/.
In the maps below, the Köppen classification was applied on temperature and precipitation averaged over shorter time scales, from interannual to decadal and 30 year. The 30 year averages were calculated with an overlap of 20 years between each sub-period, while the interannual and decadal averages did not have overlapping years. Black regions indicate areas where the major Köppen type has changed at least once during 1901–2010 for a given time scale. Thus, the black regions are likely to be sensitive to climate variations, while the colored regions identify spatially stable regions.
Major group Time scales
Interannual (%) Interdecadal (%) 30-year (%)
A 45.5 89.0 94.2
B 45.1 85.2 91.8
C 35.3 77.4 87.3
D 30.0 83.3 91.0
E 78.2 92.8 96.2
The table and images show that most places have had at least one entire year with temperatures and/or precipitation atypical for that climate. It is much more unusual for abnormal weather to persist for ten years running. At 30-years and more the zones are quite stable, such that is there is little movement at the boundaries with neighboring zones.
Over time, there is variety in zonal changes, albeit within a small range of overall variation:
Chen and Chen Conclusions
By using a global gridded temperature and precipitation data over the period of 1901–2010, we reached the following conclusions:
- Over the whole period (1901–2010), the mean climate distributions have a comparable pattern and portion with previous estimates. The five major groups A, B, C, D, E take up 19.4%, 28.4%, 14.6%, 22.1%, and 15.5% of the total land area on Earth respectively. Since the relative changes of the areas covered by the five major groups are all small on the 30 year time scale, the agreement indicates that the climate dataset used overall is of comparable quality with those used in other studies.
- On the interannual, interdecadal, and 30 year time scales, the climate type for a given grid may shift from one type to another and the spatial stability decreases towards shorter time scales. While the spatially stable climate regions identified are useful for conservation and other purposes, the instable regions mark the transition zones which deserve special attention since they may have implications for ecosystems and dynamics of the climate system.
- On the 30 year time scale, the dominating changes in the climate types over the whole period are that the arid regions occupied by group B (mainly type BWh) have expanded and the regions dominated by arctic climate (EF) have shrunk along with the global warming and regional precipitation changes.
Summary: The Myth of “Global” Climate Change
Climate is a term to describe a local or regional pattern of weather. There is a widely accepted system of classifying climates, based largely on distinctive seasonal variations in temperature and precipitation. Depending on how precisely you apply the criteria, there can be from 6 to 13 distinct zones just in South Africa, or 8 to 11 zones only in Hawaii.
Each climate over time experiences shifts toward warming or cooling, and wetter or drier periods. One example: Fully a third of US stations showed cooling since 1950 while the others warmed. It is nonsense to average all of that and call it “Global Warming” because the net is slightly positive. Only in the fevered imaginations of CO2 activists do all of these diverse places move together in a single march toward global warming.