Sometimes it's just too hot to do anything, let alone work. If climate change continues, that might be the case more often.

Researchers think rising temperatures could diminish global economic productivity -- not because people will stop working altogether, but because productivity slows down when the mercury rises.

In a new study published in Nature, scientists from Stanford and the University of California, Berkeley looked at global warming through a macroeconomic lens. Several studies have tallied up the logistical and infrastructure costs of climate change -- the price tag for city-destroying floods and farm-killing droughts. But Stanford scientists looked at how rising temperatures will affect people's productivity.

This isn't necessarily uncharted territory. Companies looking to get an edge in the hyper-productive world of modern commerce have funded numerous studies on the ideal office temperature. The consensus is 70 degrees Fahrenheit. When it's too hot or too cold, workers become less efficient and prone to error.

"Many very careful studies show clearly that high temperatures are bad for things like agriculture and labor productivity, even in rich countries," study co-author Marshall Burke, a professor of Earth system science at Stanford, explained in a press release. "While these relationships showed up again and again in the micro data -- for example, when looking at agricultural fields or manufacturing plants -- they were not showing up in the existing macro-level studies, and we wanted to understand why."

To bridge the gap, Burke and his fellow researchers took a wide-angle view, compiling and analyzing temperature averages and economic output data from 166 countries between 1960 and 2010.

They discovered a bell curve. Rising temperature encourages productivity up to a threshold, an annual average temperature of 55 degrees Fahrenheit. Anything hotter and productivity begins to slack and drop off.

"Our macro-level results lined up nicely with the micro-level studies," said co-lead author Solomon Hsiang, a public policy professor at Berkeley.

But projecting the productivity costs of a warming climate isn't easy, researchers say. Some theorize that wealthier nations will be able to use technology to adapt and counteract downward trends in productivity. But scientists say there's little evidence for such a theory in the historical data.

"The data definitely don't provide strong evidence that rich countries are immune from the effects of hot temperatures," Hsiang said. "Many rich countries just happen to have cooler average temperatures to start with, meaning that future warming will overall be less harmful than in poorer, hotter countries."

Hsiang and his colleagues think economic output and global incomes could shrink anywhere from 20 to 40 percent, depending on how well governments are able to mitigate global warming.

Poorer countries will likely be hit the hardest, as most underdeveloped nations are in the tropics, places that have already passed the temperature threshold.