#ClimateChange: Why a half-degree temperature rise is a big deal — NASA


From NASA’s Jet Propulsion Laboratory (Bob Silberg):

Corn plants with no corn

Why does a half degree of temperature increase make such a difference to some of the crops that were studied? For one thing, a half degree averaged out over the whole world can mean much more of an increase in some locations and at certain times.

“Most of that temperature change may occur during a small fraction of the year, when it actually represents conditions that could be 5 or 10 degrees warmer than pre-industrial temperatures instead of just 1.5 or 2 degrees warmer,” said Dave Schimel, who supervises JPL’s Carbon Cycle and Ecosystems group.

“There are places in the world where, for these important breadbasket crops, they are already close to a thermal limit for that crop species,” Schimel said. Adding to the burden, he said, “this analysis (the EGU study) does not take into account the fact that pests and pathogens may spread more rapidly at higher temperatures.”

And Schimel pointed out that heat can imperil agriculture even when crops don’t die. “If you get really high temperatures or very dry conditions during critical parts of the development of the crop, it produces essentially no grain. For example, above certain temperature thresholds, corn doesn’t die but it doesn’t grow seed. It doesn’t grow a corncob. And other crops are similar to that, where the development of the actual food part of the crop is dramatically inhibited above critical temperatures.”

But what about that fertilization effect from carbon dioxide? “It does help a bit, but it doesn’t make the underlying problem go away,” he said. “And by the way, if the plant was growing really fast when it died, it still died.”

Can we avoid the extra half-percent temperature increase? Schimel agrees that we should try hard to do so, but cautions that we don’t know how to fine-tune global warming with that much precision. “If we aim for 2 degrees, we might hit 3 degrees,” he said. “If we aim for 1.5 degrees, we might still hit 2 degrees.”

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