Our atmosphere isn't just warming up; it's getting more acidic, too. Atmoshperic scientists at the University of Washington analyzed ice cores drilled in Greenland, and found that ever since we started burning coal and driving cars, there's been a spike in the acidity of the atmosphere.
Ice cores are enormous frozen cylinders extracted from permanent ice sheets that contain what is essentially a record of the planet's air, and climatologists use them to get a better picture of what the atmosphere looked like in decades and centuries past. Ice cores are one of our best sources of paleoclimate data. Along with tree rings, coral, and lakebed sediment, they allow us to chart the increasing concentration of carbon dioxide in the atmosphere, and to compare the chemical composition of air to pre-industrial times.
But Lei Geng and his fellow researchers at U.W. weren't focusing on the carbon content of the frozen air prisons. Instead, they discovered that an increase in emissions of sulfur dioxide and nitrates—starting at the the beginning of the Industrial Revolution—has been acidifying the atmosphere long before anyone was talking about acid rain..
From the University of Washington's report, entitled 'Greenland ice sheet carries evidence of increased atmospheric acidity,':
The gradual buildup of acidity in the atmosphere over a century got a boost around 1950 with a sharp increase in nitrogen-oxygen compounds, referred to as NOx, mainly produced in high-temperature combustion such as occurs in coal-fired power plants and motor vehicle engines. NOx is easily converted to nitric acid in the atmosphere, further increasing the acidity.
This means, among other things, that the "growing acidity in the atmosphere was occurring decades before acid rain was recognized as a threat, particularly in industrial areas of North America." Ever since we've been burning fossil fuels, we'd been upping the acidic ante. And there may be further unforseen impacts yet.
Ice core data show concentrations of nitrate (top line), hydrogen ions (middle line) and nitrogen-15 (bottom line) from 1772 through 2006
“It changes the chemical properties of the lower troposphere, where we live, and that can have a lot of consequences,” Geng said today while presenting the findings.
Thankfully, the Clean Air Act, and analgous laws around the world, have helped rein in sulfur dioxide pollution—according to the study, sulfates in the atmosphere are now back down to pre-Industrial Revolution levels—which were a major cause of acid rain. But nitrates are still a problem. As the paper notes, there's been "an increase in nitrates associated with the burning of fossil fuels," that continues to this day. The American Environmental Protection Agency has plans to clamp down on NOx emissions in power plants, which should be a good start.
If we keep emitting fossil fuels worldwide in the manner we have been, we may see more than one kind of extreme weather—droughts, hurricanes, floods, sure. But imagine adding a more acidic atmosphere back into the picture. Now we're getting apocalyptic.