Plants, animals and agricultural systems have adapted to thrive in certain climates, be they arid or wet, tropical or temperate.

At the globe warms, those climates will shift, potentially disrupting ecosystems and agriculture. A study published yesterday in the journal Nature Climate Change shows for the first time that the shift will happen faster the more the globe warms.

Before she did the study, Irina Mahlstein, a climate scientist at the University of Colorado, Boulder, anticipated that the relationship between warming and climate zone change would be linear. Each degree of warming would lead to a certain amount of the Earth's land area changing its climate zone.

But that was not what Mahlstein found when she used model data to predict changes in climate zones.

"That was a big surprise for us," she said.

"The implications of this nonlinear relationship is that the pace, how fast these changes are happening or how often they are happening, is increasing the warmer the Earth gets."

The faster the pace of that shift, the less time plants, animals and agriculture systems have to adjust.

Mahlstein's analysis shows that if the globe warms 2 degrees Celsius, which is the amount often seen by scientists as a threshold to avoid catastrophic results, 5 percent of the land on the Earth shifts to a new climate zone.

But if it warms 2 degrees more, 10 percent of the land area experiences a climate shift.

Mahlstein did this analysis by using data from 13 atmosphere-ocean climate models, running them from 1900 to 2098, and tracking how climate zones changed. She went into the past to ensure the models were accurately representing the shifts and calibrated the data using what was known about how climate zones have shifted in the past.

Coffee and cacao could be early victims
Another new aspect of the research, she pointed out, was the finding that in lower latitudes, like the subtropics, the mountainous areas are most vulnerable to climate zone change due to global warming.

"That's always been thought of, but it's never been shown," she said.

Coffee and cacao are two significant crops grown in the mountainous tropical regions that could be affected by climate shifts.

Mahlstein was clear on the limitations of the study, noting that, for example, climate models have a hard time predicting changes in precipitation.

On the other hand, she found that temperature was the primary driver of shifts in climate zones. Climate models are much better at calculating average temperature change, said John Daniel, a co-author on the paper and a researcher at the National Oceanic and Atmospheric Administration's Earth System Research Laboratory.

"The zones get crossed more readily when you change temperature; you have to change precipitation a lot" in order for the climate zone to change, Daniel said.

One of the results the researchers were looking for in their analysis and did not find, he added, was evidence of a threshold effect, that after 2 degrees or some set amount of warming, there would be big shifts in climate zones.

"Even if there were thresholds for particular climate zones, that might be an interesting thing to study further," he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500