A warming climate is having a profound effect on humanity’s ability to feed itself. Higher temperatures are dramatically changing where it’s ideal, or even possible, to grow staple crops, especially in the tropics. More extreme weather makes crop failures more likely.

That’s already made global warming a reason for the reversal of a decade-long decline in the global number of undernourished people, write the editors of the book How to Feed the World. The UN’s Food and Agriculture Organization reports that the number of undernourished people rose 5% between 2014 and 2017 to an estimated 821 million people.

The book’s editors call agriculture a “Goldilocks industry” that is first to experience global warming’s worst effects on human society. Poor countries may be hit hardest by extreme rainfall, drought, and storms, but the industrialized world is not immune. Severe weather in the US midwest brought 30% more heavy rainfall events between 1958 to 2012, and a 2012 heatwave knocked corn harvests back to yields not seen since the 1990s.

It’s only getting hotter. Our planet has set heat records every year since 2014. After a century in which the Earth’s surface warmed about 1° Celsius (1.3–1.6° Fahrenheit), the rate of warming nearly doubled starting in 1975, according to the international State of the Climate in 2017 report. What happens next? Rich countries will try to adapt, although the costs will be high. In poor regions, analysts say, regional wars, desperate migrants and food riots (like the ones the 2007—2008 crop crisis sparked in more than 70 countries) are in store.

Of course, we have a choice, according to the Intergovernmental Panel on Climate Change (IPCC). “Limiting warming to 1.5°C is possible within the laws of chemistry and physics but doing so would require unprecedented changes,” said Jim Skea of Imperial College London and an IPCC co-author.