Has climate change already impacted global agriculture? 

From the raging fires in Australia to the devastating superstorms in the United States, the signs of a changing climate are growing clearer by the day. Over the past few decades, the field of climate change impact assessment— the use of statistics and climate models to calculate the impact of climate change on our society— has helped reveal the potential consequences of unregulated climate change on global agriculture. 

In a recent paper in Nature Climate Change, a research team led by Cornell professor Dr. Ariel Ortiz-Bobea uses a climate change impact assessment to ask: is our agricultural system already experiencing the impacts of climate change? It is clear that global temperature has already risen by 1℃ from pre-industrial levels; however, linking this rise in temperature to tangible economic losses is not an easy task. 

To answer this complicated question, the authors focus on agriculture—or more precisely, on the productivity of agriculture. Productivity is a measure of aggregate output, such as bushels of corn or tons of meat, produced for a fixed set of inputs, such as pounds of fertilizer or acres of land. Development of new technologies (e.g., high-yield crop varieties) has led to significant improvements in this productivity. The researchers seek to determine whether climate change has already slowed this growth. In other words, they ask whether the world would have achieved a larger crop production given the same inputs, without the change in climate. To answer this question, the researchers construct a scenario of a “human-free” Earth, which simulated what the Earth’s climate would have been like if there were no human-caused greenhouse gas emissions. 

The authors found that indeed, on an Earth without human-induced climate change, cumulative agricultural productivity would be 20 percent higher than our current productivity. Furthermore, the authors found convincing evidence that climate change has not impacted all countries equally. Historically low-income countries in Africa and in Central America experienced the greatest gap in productivity growth. 

Such findings are even more alarming if we consider that global agriculture has become increasingly sensitive to extreme weather. Dividing the five-decade period into two quarter-centuries, the authors found that agriculture globally has become more vulnerable to weather shocks in the second period (1989 to 2015) than in the first (1962 to 1988). The findings are based on an elaborate economic model that removes country-specific trends and global economic events (such as economic recessions) and remain valid regardless of data source or calculation methods. 

The future-oriented nature of global temperature targets—limiting end-of-century temperature rise to 1.5℃ levels, for example—may give the impression that climate change is a problem of the future. Ortiz-Bobea et al.’s study carefully teases out the impact of past climate change on global agricultural productivity. What they find is that such beliefs are misguided—climate change is here to stay, and it has already chipped away at our food production system for the last few decades. From the adoption of heat-resilient crops to streamlining food supply chains, the time to protect agriculture from further climate change is now.