May 15, 2014

Climate Change and Food Production

A friend recently asked whether more carbon dioxide in the atmosphere would help plants grow faster. If you've wondered the same thing, the research is clear that hotter and dryer conditions have dire impacts on plant growth. 

Plants die quite rapidly without water - and we are seeing unprecedented drought conditions throughout much of California and the Midwest where most of our food is grown - as a result of climate change. 

Even with adequate water supplies, high temperatures cause significant yield loss in our crops. And extended heat waves of 4 days or longer, even with irrigation, devastate crop yields. 

It was 102 degrees on Sunday May 4th in Kansas where we grow a lot of our wheat. This is the hottest temperature ever recorded during the month of May in Kansas.  Those record temperatures continued 4 days through Wednesday. The earliest we've previously seen 102 degrees in Kansas was on June 2nd - almost a whole month later.

On top of that, Kansas has had the least rain this season since the time records have been kept - even worse than during the Dust Bowl year of 1936. 

The combination of the worst drought in recorded history and the hottest temperatures in recorded history are happening right now - in Kansas - America's bread basket. This is not some distant future effect of climate change. This is now. This is affecting our food supply this year. 

For those who like peer reviewed data, here is some academic research to back up the common sense understanding that the combination of scorching heat waves and drought conditions result in crop failures. 

Productivity of wheat and other crop species falls markedly at high temperatures. All stages of development are sensitive to temperature. It is the main factor controlling the rate of crop development. [FAO - Food and Agriculture Organization]
For every 1°C rise in temperature, there is a depression in grain yield by 8 to 10%, mediated through 5 to 6% fewer grains and 3 to 4% smaller grain weight.
While a linear model works well to describe wheat development as long as temperatures remain within 10 to 30°C, a non-linear model as in Figure 6.1 [shown below] is needed to describe development when a crop is exposed to extreme temperature stress.
This chart shows growth rate of wheat vs temperature. Wheat grows well till temperatures reach 86 degrees F, after that productivity falls off rapidly. 

With high night temperatures (in the 70s or 80s) more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels or seeds, thereby lowering potential grain yield. Low night temperatures during grain fill have been associated with some of Ohio's highest corn yields in past years. Soybean plants subjected to a night temperature of 85°F resulted in a 10% yield loss.  Corn subjected to 85°F at night experienced grain yield reductions of 40%. [Ohio State University

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