Major Cereal Crops Fall Behind Because of Climate Change, Study Shows

Climate change has already held back global yields of wheat, maize, and barley by as much as 13% over the past 50 years—compared to what they would have been in a world without warming—although Canada may have dodged the worst effects so far, a new Stanford University study finds.

The authors revisit the question of how climate change affects agriculture, especially in major production regions. They say their research draws attention to the dramatic shifts farmers are facing, as well as the overall effectiveness of climate models in projecting these shifts.

They used 50 years of data comparing actual yields to what climate models predicted. Overall, global yields of wheat, maize, and barley were found to be 10%, 4%, and 13% lower than they would have been without climate change. And while past research has indicated that some climate outcomes might increase crop production, given the higher concentrations of carbon dioxide and longer growing seasons, “losses likely exceeded those benefits,” the authors write.

That wasn’t true across the board. For soybeans and rice, “carbon dioxide benefits likely exceeded climate-related losses.”

The researchers determined these connections using a regression model that compared yield anomalies with anomalies of weather, explained lead author David Lobell, an earth system science professor at Stanford. This approach allowed the researchers to suggest that the yield losses were caused by climate change—rather than just correlated with them—as long as it is accepted that yield anomalies do not cause weather anomalies and that no unobserved factor is driving both sets of changes.

Lobell told The Energy Mix the study deliberately didn’t use a trend analysis, which focuses on changes of one variable over time, because there are so many other factors correlated over time with yield and weather.

“The regression models are used to isolate the effect of weather on yield,” he said. “Then these models can be used to estimate what would have occurred without the trends.”

‘Warming Hole’ Spared Canadian Yields

Yield losses were mostly in line with what models would have predicted, but with two main exceptions. For one, North American crop production in Canada and the United States was less affected than in other regions of the world, and also less than what models show. The study chalks this up to a “warming hole” that has spared the continent from more significant climate impacts, though researchers are unclear about why the phenomenon exists, or how long it will persist.

Secondly, increases in regional vapour pressure deficits (VPD), the difference between the amount of moisture that’s actually in the air and the amount of moisture that air could hold at saturation, have been consistently underrepresented in climate models. VPD can be a main driver of stress on plants and high deficits can reduce growth.

The findings have implications for both climate research and agriculture adaptation. The revealed yield changes indicate how climate change is likely to affect food production systems. The study also sheds light on how models can be improved, and helps quantify the damage or benefits of historical emissions, supporting efforts to develop financial mechanisms for compensating affected communities. The research also informs breeding and adaptation efforts by tracking “the relative speed with which specific climate stresses are changing, or certain crops or regions are being affected.”

Cover photo:  cjuneau/flickr