While coal remains the world's largest source of electricity, its use is in decline across North America, as both Canada and the U.S. shut down coal plants in favour of the less-polluting natural gas.

And now, for the first time, researchers are painting a clear picture of what happens to the surrounding region, and the people and farms in it when a coal plant shuts down.

A study published in the journal Nature Sustainability, looked at hundreds of counties across the United States as local coal-fired power plants were decommissioned. They found that the shift away from coal saved an estimated 26,610 lives and 570 million bushels of crops over an 11-year period.

"The first [reaction] was I'm not surprised. We know that these types of pollutants are bad. We know that coal plants produce them," said study author Jennifer Burney. "The other reaction was kind of a, holy crap. These are huge numbers."

Exhaust gases rise from the chimney of a coal power plant in Germany. (Jens Schlueter/Getty Images)

Burney, an environmental scientist from the University of California, San Diego, was confident in the link because the data was consistent across hundreds of locations across the U.S.

"We looked at the changes in mortality before and after, or the changes in crop yields before and after, or changes in pollution before and after in these locations, and compare them to other places in the country that didn't have a coal unit shut down," Burney told Quirks & Quarks host Bob McDonald.

The results were clear:

"Deaths dropped and crop yields went up."

The impact of air pollution on human health and mortality is probably not surprising. The impact on crop yields has been less well understood.

Air pollution affects agricultural production by blocking incoming sunlight and creating ozone, which causes tissue damage in crops. The study found the effects were greatest closest to the decomissioned plants, but were detectable up to 200 kilometres away. The study found that pollution depressed crop yields by up to seven per cent.

While these results apply only to the U.S., Burney expects that the same thing could be affecting food supplies globally, including in heavy coal-using countries like India and China, and could be having a significant effect on the global food supply.

"I do feel like it's almost like a weighted blanket just pushing yields down a little bit all over the world."