In a matter of hours, Hurricane Maria wiped out 80 percent of the crops in Puerto Rico, a devastating blow to the island’s food production. Climate change promises even more catastrophes, but also shifts in everything from temperatures to fishing grounds. Here are some of the ways climate change will create new challenges in the future, according to Timothy Griffin, director of the Friedman School’s Agriculture, Food and Environment Program, and Avery Cohn, the William R. Moomaw Assistant Professor of International Environment and Resource Policy at the Fletcher School of Law and Diplomacy.


It’s not so much an average increase or decrease in rainfall that worries farmers—it’s the extreme events. When heavy rains fall outside the growing season and crops are not there to protect the soil, soil erosion and the leaching of nutrients into lakes, streams, and oceans are the results. These changes have already begun: In New England, the number of days where it has rained more than an inch in 24 hours has increased significantly in the last 25 years.

Corn Field


Responding to environmental pressures, yields for many crops will fall. In addition, yields are likely to be variable from one year to the next. Yields could go up in a few places where certain crops would benefit from warmer weather, but don’t expect new farms to suddenly spring up in northern latitudes: Bringing new land into agriculture, building infrastructure, and creating businesses to bring products to market could take decades. Plus, clear-cutting itself contributes to climate change, accounting for 15 percent of worldwide carbon emissions.


Not only will insects that attack crops and livestock expand their territories as temperatures rise, they will hang around longer. If winters aren’t cold enough to kill off pests, farmers may have to spend months, rather than weeks, battling infestations. Several weed species thrive in warmer, CO²-rich environments, which could force farmers to use more pesticides and herbicides. While that may be disconcerting for consumers, it’s an even bigger threat to farm workers, who face significant health risks from overexposure to the chemicals.


We all know that plants need carbon dioxide to grow. But recent research has shown that some plants, when exposed to extra CO² in the atmosphere, grow up to have lower concentrations of protein and minerals like zinc and iron. That might not cause malnutrition in the United States, but it could have a significant impact in poorer countries where diets consist of just a few staple foods.



In the northern United States, a warmer and wetter climate could encourage more pathogens in dairy cattle and pigs. In the South, farmers will have to pay to cool buildings that house chickens and pigs. Over time, heat stress reduces fertility and milk production, and a series of very hot days can kill animals outright—if average temperature rise just a few degrees Celsius, as some models forecast, it may be too hot to raise cows in Texas within 50 years. Farm workers will suffer, too, as recent research on heat stress points not only to lost productivity but serious health concerns for people who work outside.


Fish are keenly attuned to water temperature for mating and migration cues, so expect to see big changes in traditional ranges. Scientists have already seen shifts in the Gulf of Maine, which is warming faster than just about every other ocean in the world, and is predicted to rise another 6.7 degrees Fahrenheit over the next 80 years. In other waters, higher temperatures have brought diseases and parasites in oysters, salmon, and abalone. Carbon dioxide in the atmosphere leads to acidity in the ocean, which harms coral, the ecosystem bedrock, and weakens shellfish.


We can forestall some of these negative effects by changing how and where we grow things. But the groups that are most likely to be affected by climate change are the groups that have the fewest resources to respond. Poor farmers in developing country who don’t have access to mitigating technology—and the money to pay for it—will face enormous challenges. Poverty is ingrained in agriculture. According to the World Bank, nearly two-thirds of extremely poor workers aged 15 and above work in the agricultural sector.


The United Nations Development Program predicts that major losses in agricultural production will increase malnutrition, lower incomes, and make it harder to reduce poverty. Developing countries are likely to become more dependent on imports, with their farmers losing market shares in agricultural trade. Farmers in developing regions around the world, and in sub-Saharan Africa in particular, face a sort of double jeopardy, not just from climate change, but also from conflict that may arise in response to it. Rising food prices have led to political instability, as we saw with the riots in Asia and Africa after food-price shocks in 2008.



Farmers and ranchers around the world are already adapting to the new weather patterns they see. They are introducing new crop varieties with resistance to heat, drought, or salinity or choosing fast-maturing varieties that adapt to shorter growing seasons. They are harvesting and conserving water and using more efficient sprinklers and drip irrigation.


Data is transforming agriculture, from production systems that track yield and variability to market-focused systems that communicate pricing variations to users. Almost everyone has access to a smartphone, so it’s not unreasonable to envision a time when a farmer anywhere in the world can upload data from a soil sample and get an analysis back quickly. And as we gather more data, our estimates of climate risk and the social costs of climate change are getting better. Our assessments will be important for determining whether it’s rational to mitigate emissions, and possibly raise ambition for taking action.