Farmers are used to dealing with weather, but climate change is making it harder by altering temperature and rainfall patterns, as in this year’s unusually cool and wet spring in the central U.S. In a recently published study, I worked with other scientists to see whether climate change was measurably affecting crop productivity and global food security.
To analyze these questions, a team of researchers led by the University of Minnesota’s Institute on the Environment spent four years collecting information on crop productivity from around the world. We focused on the top 10 global crops that provide the bulk of consumable food calories: Maize (corn), rice, wheat, soybeans, oil palm, sugarcane, barley, rapeseed (canola), cassava and sorghum. Roughly 83 percent of consumable food calories come from just these 10 sources. Other than cassava and oil palm, all are important U.S. crops.
We found that climate change has affected yields in many places. Not all of the changes are negative: Some crop yields have increased in some locations. Overall, however, climate change is reducing global production of staples such as rice and wheat. And when we translated crop yields into consumable calories – the actual food on people’s plates – we found that climate change is already shrinking food supplies, particularly in food-insecure developing countries.
Adding up local trends
The first thing we needed to understand was how temperature and precipitation influenced crop productivity in many locations. To do this, we analyzed data from up to 20,000 counties and districts around the world to see how crop yields varied in each place with changes in precipitation and temperature.
Once we had constructed an empirical model connecting crop yield to weather variations at each location, we could use it to assess how much yields had changed from what we would have expected to see if average weather patterns had not changed. The difference between what we would have predicted, based on the counterfactual weather, and what actually occurred reflects the influence of climate change.
Our analysis showed that climate change has already affected crop yields around the world. There were variations between locations and among crops, but when all of these different results were totaled, we found yields of some important global staples were already declining. For example, we estimated that climate change was reducing global rice yields by 0.3% and wheat yields by 0.9% on average each year.
In contrast, some more drought-tolerant crops have benefited from climate change. Yields of sorghum, which many people in the developing world use as a food grain, have increased by 0.7% in sub-Saharan Africa and 0.9% yearly in western, southern and southeastern Asia due to climate shifts since the 1970s.
A mixed US picture
In the United States corn and soybeans are important cash crops, with a combined value of more than US$90 billion in 2017. We found that climate change is causing a small net increase in yields of these crops – on average, about 0.1% and 3.7% respectively each year.
But these numbers reflect both gains and losses. In some Corn Belt states, such as Indiana and Illinois, climate change is shaving up to 8% off of annual corn yields. At the same time, it has boosted annual yields in Iowa and Minnesota by approximately.
