Globally, humanity is producing more food than ever, but that harvest is concentrated in just a handful of breadbaskets.

More than one-third of the world’s wheat and barley exports come from Ukraine and Russia, for example. Some of these highly productive farmlands, including major crop-growing regions in the United States, are on track to see the sharpest drops in harvests due to climate change.

That’s bad news not just for farmers, but also for everyone who eats — especially as it becomes harder and more expensive to feed a more crowded, hungrier world, according to a new study published in the journal Nature.

Under a moderate greenhouse gas emissions scenario, six key staple crops will see an 11.2 percent decline by the end of the century compared to a world without warming, even as farmers try to adapt. And the largest drops aren’t occurring in the poorer, more marginal farmlands, but in places that are already major food producers. These are regions like the US Midwest that have been blessed with good soil and ideal weather for raising staples like maize and soy.

But when that weather is less than ideal, it can drastically reduce agricultural productivity. Extreme weather has already begun to eat into harvests this year: Flooding has destroyed rice in........

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