Human-induced climate change has stunted global agricultural productivity by 20.8% since 1961, a new study found, and with rapidly increasing temperature rises and a growing population, researchers say the ripple effects will only intensify.
Looking at total factor productivity data from 172 countries over the study period, the researchers found that the hits to global agriculture were less severe in cooler regions — North America, Europe and Central Asia — and more severe in sub-Saharan Africa, North Africa and the Near East, Latin America and the Caribbean. Moreover, when they restricted the analysis to data from 1989 to 2015, they found the global effect was even worse — 30% — suggesting that accelerating climate change was creating more damage as the effects became more severe.
"There's so much emphasis on the future, and we're like, OK, but it's not just about future generations, it's about the current ones," said Ariel Ortiz-Bobea, an associate professor at Cornell University and the lead author of the paper, published April 1 in Nature Climate Change. "We're not that great as humans to think about contrafactuals at this big scale. We get used to the new normal. I think it's important just to quantify and show what this 'new normal' really means."
Total factor productivity is a measure of both agricultural output — including crops and livestock commodities — and inputs — including land, labor, machinery, feed and fertilizer, and the researchers estimate that without climate change, the world would have reached 2020's TFP levels in 2013; thus, the world is seven years behind.
Productivity increased over the six decades they examined, which masked the damaging effect of climate change. "It's like a headwind," Ortiz-Bobea told The Academic Times. "It's slowing you down. You might not even realize it, because you're not seeing the contrafactual."
The slowdown is worsening as the global population is projected to reach 9.7 billion people by 2050, and all those people need to eat — in an article published in the Proceedings of the National Academy of Sciences in 2011, researchers estimated that from 2005 to 2050, global food demand would rise by 100-110%.
Ortiz-Bobea pointed out that research and development in agriculture "takes decades to lead to new commercial technologies that are adopted by farmers."
Using data from the U.S. Department of Agriculture's international TFP dataset, the researchers established a connection between total factor productivity and average weather. Weather data came from Princeton University's Global Meteorological Forcing Dataset on daily minimum and maximum temperature and total precipitation over the study period; for this study, the researchers averaged weather to monthly levels for each country.
For their contrafactual analysis, they used the World Climate Research Programme's Coupled Model Intercomparison Project Phase 6 simulations of the weather patterns that would likely exist without the effects of climate change caused by human activity.
To ensure that outliers weren't skewing the data, the researchers repeated the test excluding certain large countries — China, the U.S., India or Brazil — the 10% coldest or hottest countries, or portions of the countries with small agricultural revenues, and kept finding a similar result: Climate change was dragging down productivity. They also conducted placebo tests, scrambling the data to make sure the relationship between weather and TFP "was not a fluke," Ortiz-Bobea said.
When the researchers analyzed the effect on output alone, rather than inputs and outputs captured by TFP, they found that climate change decreased output by 27.6%. Because that result was larger than the 20.8% hit to TFP, "It showcases that farmers are indeed responding to weather conditions," Ortiz-Bobea said, by adjusting their investments into agriculture in response to climate change, which wasn't immediately clear in the TFP calculations.
"I was surprised by the magnitude of the results," Ortiz-Bobea said, explaining that he would have guessed climate change caused a 5% slowdown in TFP rather than 20.8%. "What can I hope that comes out of this? I think it's a realization for people that this is not something that is 50 years down the road. This already happened. It's just the magnitude is gonna keep rising. That's what I really hope people realize."
The study, "Anthropogenic climate change has slowed global agricultural productivity growth," published April 1 in Nature Climate Change, was authored by Ariel Ortiz-Bobea, Toby R. Ault and Carlos M. Carrillo, Cornell University; Robert G. Chambers, University of Maryland; and David B. Lobell , Stanford University.
Correction: An earlier version of this story described the slowdown as a decrease. It is a decrease in projected productivity, not a decrease in observed productivity. The error has been corrected.