Among the many frightening consequences of a warmer world, one of the worst is what it will do to agricultural production. A new study finds that isn't just something for the future – we are already growing a fifth less food than we would if the world had maintained 1960s conditions. Technological progress has hidden this until now raising overall yields. However, as warming accelerates, agricultural scientists will have to work harder to keep up.

Even in a pandemic world population is growing by tens of millions of people annually, and that won't stop any time soon. Better distribution of food can help avoid famines to an extent, but avoiding a hungry future almost certainly means producing more food. Climate change makes that harder, but no one has been sure how much.

Professor Robert Chambers of the University of Maryland has sought to answer that question. In Nature Climate Change he concludes there has been a 21 percent reduction in global food productivity since 1961 as a result of the changing climate, including more droughts in some places and floods in others.

“Agricultural productivity measurement hasn't historically incorporated weather data, but we want to see the trends for these inputs that are out of the farmer's control," Chambers said in a statement. Previous studies of the influence of global heating on agriculture have focused on cereals as the largest source of calories, but Chambers and co-authors used the value of crops to include all foods we grow.

"We used the model in this paper to estimate what total factor productivity patterns would have looked like in the absence of climate change." Chambers added. "Our study suggests climate and weather-related factors have already had a large impact on agricultural productivity,"

The introduction of hybrid crops like dwarf wheat and more widespread use of fertilizers and machinery have made agriculture much more productive over the period Chambers studied, saving us from predicted calamities. Nevertheless, the changing climate has eaten up seven years of productivity growth.

Missing out on those potential gains has made food more expensive, leaving some to starve entirely. It's also forced farmers to expand the areas they sow, destroying ecosystems that will never come back and sending species extinct.

Chambers previously conducted a similar analysis for the United States, where he found climate effects have so far been modest compared to the advances science and engineering have brought. Expanding the assessment to the whole world showed brought worse news. Africa, Latin America, and the Caribbean, the places that can least afford losses in food production, lost 26-34 percent of their productivity as a result of climate effects. A small number of nations, mostly in central Africa, have seen total agricultural productivity fall over the last 60 years. Russia and Canada have experienced climate change-induced rises in agricultural productivity, but they're almost alone.

"Some people think about climate change as a distant problem, something that should concern primarily future generations. But this overlooks the fact that humans have already changed the climate," said first author Dr Ariel Ortiz-Bobea.