New Study Shows How Climate Change Is Already Reshaping The Earth | ThinkProgress
▻http://thinkprogress.org/climate/2015/09/03/3697620/expanding-global-dry-semi-arid-zones
A landmark study in the journal #Nature documents an expansion of the world’s dry and semi-arid climate regions since 1950 — and attributes it to human-caused global warming.
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The study uses the Köppen–Geiger climate classification system:
A: Tropical/megathermal climates
B: Dry (arid and semiarid) climates
C: Temperate/mesothermal climates
D: Continental/microthermal climates
E: Polar and alpine climates
This map shows how the world is broken down by climate and sub-climate regime :
Map of the world’s climate regimes. A new study finds the dry zones (B) are expanding while the polar/tundra zones (E) are shrinking. University of Melbourne via Wikipedia.The study looks at changes in #temperature and #precipitation to determine changes to the various climate zones over time. A region can shift to a drier B climate zone if precipitation drops — or if temperature rises. Higher temperatures cause more evaporation and dry out soil.
The authors note that of all their results, “the most conspicuous feature is a worldwide expansion of B climate (mainly semiarid) at the expense of C and midlatitude D climate” (see figure below):
Linear trends in areas of 5 major climate types for 1950–2003; asterisks denote significant trends at the 5% level. A positive trend of high-latitude (north of 55°N) D climate and a negative midlatitude (south of 55°N) D climate are over-plotted in blue with the net negative trend of D climate in dark blue 
