Rising yields hide a growing drag. Global food production has risen enormously since the 1960s, thanks to better crop varieties, fertilisers and farming technology. But climate change has been pulling the other way. A Cornell-led study found it has cut global farming productivity growth by about 21% since 1961, equivalent to losing about seven years of progress.

The CO₂ “boost” is limited. Extra CO₂ can help some crops, such as wheat, grow. But maize, one of the world’s most important staple crops, benefits very little. A NASA-led study projects maize yields could fall by up to 24% by late this century under high emissions, with clear impacts emerging within about a decade, even after allowing for the CO₂ effect. Higher CO₂ also makes staple crops such as wheat and rice less nutritious, lowering their zinc, iron and protein.

More leaves don’t mean more food. Satellites do show plants “greening” as CO₂ rises. But more leaf growth in forests and grasslands isn’t the same as more grain in a field during a heatwave or drought.

Britain is already feeling it. After a record wet autumn and winter, England had its second-worst harvest on record in 2024, according to Defra figures. Farmers can adapt to gradual change, but repeated extreme years are much harder to manage.

The real risk is shocks. Global averages can keep rising while the risk of extreme years grows. When several major growing regions are hit by heat or drought at the same time, prices spike and the poorest are hit hardest. That’s why food security experts, from the military to insurers, treat climate change as a growing threat to food supplies.