Joe Romm writes: 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.

This expansion of the world’s dry zones is a basic prediction of climate science. The fact it is so broadly observable now means we must take seriously the current projections of widespread global Dust-Bowlification in the coming decades on our current CO2 emissions pathway — including the U.S.’s own breadbasket.

The new study, “Significant anthropogenic-induced changes of climate classes since 1950,” looks at multiple datasets of monthly temperature and precipitation over time. The main finding:

About 5.7% of the global total land area has shifted toward warmer and drier climate types from 1950–2010, and significant changes include expansion of arid and high-latitude continental climate zones, shrinkage in polar and midlatitude continental climates….

As for the cause, “we find that these changes of climate types since 1950 cannot be explained as natural variations but are driven by anthropogenic factors.”

In short, humans are causing the world’s arid and semi-arid climate zones to expand into the highly populated mid-latitude continental climates (where, for instance, most Americans live) — and causing the high-latitude climates to expand into the polar zones. Of course, the polar zones are precisely where the carbon-rich frozen tundra is and the land-locked ice of the world’s biggest ice sheets and glaciers.

These are stunning changes when you consider the fact that the world has only warmed about 1°F since 1950, and we are on track to warm 5 times that much (or more) this century alone. [Continue reading…]