How will climate change affect agriculture and our ability to feed the world’s growing population? - The Years Project

Ask Joe

Joseph Romm, Ph.D. Chief Science Advisor

How will climate change affect agriculture and our ability to feed the world’s growing population?

Every part of the world will be routinely hit by extreme deluges, floods, droughts, and heat waves that damage crops. At the same time, salt water intrusion from sea level rise threatens some of the richest agricultural deltas in the world, such as those of the Nile and the Ganges. Meanwhile, ocean acidification combined with ocean warming and overfishing may severely deplete the food available from the sea.

On the demand side, the United Nations Food and Agricultural Organization estimates that some 800 million people are chronically undernourished. In the coming decades, we will be adding another billion mouths to feed, then another billion and by most projections, another billion, taking us to 10 billion. At the same time, many hundreds of millions of people around the world will be entering the middle class, and, if they are anything like their predecessors around the globe, they will be switching from a mostly grain-based diet to a more meat-based one, which can require 10 times as much acreage and water per calorie delivered.

The World Bank issued an unprecedented warning about the threat to global food supplies in a 2012 report, “Turn Down the Heat: Why a 4°C Warmer World Must be Avoided.” The Bank noted that the latest science was “much less optimistic” than what had been reported in the Intergovernmental Panel on Climate Change’s 2007 Fourth Assessment report:

These results suggest instead a rapidly rising risk of crop yield reductions as the world warms. Large negative effects have been observed at high and extreme temperatures in several regions including India, Africa, the United States, and Australia. For example, significant nonlinear effects have been observed in the United States for local daily temperatures increasing to 29°C for corn and 30°C for soybeans. These new results and observations indicate a significant risk of high-temperature thresholds being crossed that could substantially undermine food security globally in a 4°C world.

And that’s just temperature rise: “Compounding these risks is the adverse effect of projected sea-level rise on agriculture in important low-lying delta areas.” Moreover, we have the threat to seafood of ocean acidi cation. Finally, we have Dust-Bowlification:

The report also says drought-affected areas would increase from 15.4% of global cropland today, to around 44% by 2100. The most severely affected regions in the next 30 to 90 years will likely be in southern Africa, the United States, southern Europe and Southeast Asia, says the report. In Africa, the report predicts 35% of cropland will become unsuitable for cultivation in a 5°C world.

What is some of the underlying science behind these conclusions? Using a “middle of the road” greenhouse gas emissions scenario, a study in Science found that for the more than five billion people who will be living in the tropics and subtropics by 2100, growing-season temperatures “will exceed the most extreme seasonal temperatures recorded from 1900 to 2006.” The authors of “Historical Warnings of Future Food Insecurity with Unprecedented Seasonal Heat” conclude that “Half of world’s population could face climate-driven food crisis by 2100.”

A study led by MIT economists found that “the median poor country’s income will be about 50% lower than it would be had there been no climate change.” That finding was based on a 3°C warming by 2100, which is much less than the warming we are currently on track to reach. A further study led by NOAA scientists found that several regions would see rainfall reductions “comparable to those of the Dust Bowl era.” Worse, unlike the Dust Bowl, which lasted about decade at its worst, this climate change would be “largely irreversible for 1,000 years after emissions stop.” In other words, some of the most arable land in the world would simply turn to desert.

In my Nature article, “The Next Dust Bowl,” I wrote, “Human adaptation to prolonged, extreme drought is dif- cult or impossible. Historically, the primary adaptation to dust-Bowlification has been abandonment; the very word ‘desert’ comes from the Latin desertum for ‘an abandoned place’.” During the relatively short-lived U.S. Dust Bowl era, some 2.5 million people moved out of the Great Plains.

However, now we are looking at multiple, long-lived droughts and steadily growing areas of essentially nonarable land in the heart of densely populated countries and global breadbaskets. In a 2014 study, “Global warming and 21st century drying,” the authors concluded, “An increase in evaporative drying means that . . . important wheat, corn and rice belts in the western United States and southeastern China, will be at risk of drought.”

The study’s lead author, Dr. Benjamin Cook, a top drought expert with joint appointments at NASA and Columbia, explained to me that we are headed into a “fundamental shift in Western hydro-climate.” This drying includes the agriculturally rich Central Plains. The study warns that droughts in the region post-2050 “could be drier and longer than drought conditions seen in those regions in the last 1,000 years.” Given how rapidly growing the population of the West is, I asked him whether there would be enough water for everyone there. He said “we can do it,” but only “if you take agriculture out of the equation.” However, that, of course, is not an option. Columbia University’s Lamont-Doherty Earth Observatory further notes that “while bad weather periodically lowers crop yields in some places, other regions are typically able to compensate to avert food shortages. In the warmer weather of the future, however, crops in multiple regions could wither simultaneously.” That would make food-price shocks “far more common,” according to climatologist and study coauthor Richard Seager.

The international aid and development organization Oxfam has projected that global warming and extreme weather will combine to create devastating food price shocks in the coming decades. They concluded that wheat prices could increase by 200% by 2030 and corn prices could increase a remarkable 500% by 2030.

In 2014, the IPCC warned that humanity is risking a “breakdown of food systems linked to warming, drought, flooding, and precipitation variability and extremes.” This was a key conclusion from its summary of what the scientific literature says about “Impacts, Adaptation, and Vulnerability,” which every member government approved line by line. The IPCC pointed out that in recent years, “several periods of rapid food and cereal price increases following climate extremes in key producing regions indicate a sensitivity of current markets to climate extremes among other factors.” So warming-driven drought and extreme weather have already begun to reduce food security.

If we jump to a more heavily populated and climate-ravaged future, the IPCC warns that climate change will “prolong existing, and create new, poverty traps, the latter particularly in urban areas and emerging hotspots of hunger.” You might think the question of the future of agriculture under high levels of warming would be something that has been well studied because of the importance of feeding so many people in a globally warmed world. However, the IPCC notes that “Relatively few studies have considered impacts on cropping systems for scenarios where global mean temperatures increase by 4°C [7°F] or more.”

Even though humanity is currently headed towards 4°C [7°F] and beyond, we do not have a very good scientific picture of the full impact such climate change will have on agriculture and food supplies. The IPCC does mention briefly that our current path of unrestricted carbon emissions (the RCP8.5 scenario) holds unique risks for food supplies: “By 2100 for the high-emission scenario RCP8.5, the combination of high temperature and humidity in some areas for parts of the year is projected to compromise normal human activities, including growing food or working outdoors.” If we warm anywhere near that much—some 4°C [7°F] or more—the challenge of feeding 9 billion people or more will become exponentially harder.