The Coming Haze of Global Warming - Pacific Standard

The Coming Haze of Global Warming

Models suggest atmospheric aerosol concentrations will increase as the temperatures keep climbing—and that's bad news for your lungs.
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Mount Rainier through the haze. (Photo: Jenny Lee Silver/Flickr)

Mount Rainier through the haze. (Photo: Jenny Lee Silver/Flickr)

Mount Rainier towers more than 14,000 feet above sea level, so you would think it would be easy to spot from nearby Seattle, at least on a clear day. But smog often collects at the southern end of the Puget Sound, creating a veil of haze that renders the mountain invisible when viewed from the north.

Now, climatologists report, that sort of haze could be in everyone's future, not just Seattle's, as a result of global warming—and that haze, mostly fine particulate matter, could pose a threat to our lungs and overall health.

Hear the words "global warming," and most likely you'll think up images of greenhouse gases trapping heat from the sun, warming the planet. But as the climate warms, Robert Allen, William Landuyt, and Steven Rumbold explain today in Nature Climate Change, there will also be changes in concentration of aerosols—tiny particles including dust, salt, sulfates, black carbon, and other sources of air pollution.  The trouble is, previous efforts to understand how global warming affects aerosol concentrations in the air have come to mixed conclusions.

Aerosol concentrations are almost certainly going to go up, likely by about 10 percent over the next century.

Allen, Landuyt, and Rumbold aimed to remedy that situation, starting by using the most current models included in the Atmospheric Chemistry and Climate Model Intercomparison Project, which aims to improve researchers' understanding of the natural processes governing aerosols, ozone, and gases (other than carbon dioxide) in the atmosphere. Ultimately, the hope is that ACCMIP predictions will be incorporated into more general climate models, such as those used by the Intergovernmental Panel on Climate Change in its climate assessment reports.

In the meantime, Allen and his colleagues wanted to see what ACCMIP models had to say about the link between global warming and air pollution, so they ran computer simulations of those models for the years 2000 and 2100, and compared the results. Despite the models' varying assumptions and parameters, they all came to basically the same conclusion: Aerosol concentrations are almost certainly going to go up, likely by about 10 percent over the next century. The results from two other models, known as CAM4 and CAM5, were much the same.

So where are all the aerosols coming from? Natural processes kick dust and sea salt into the air, and cars and manufacturing produce sulfates and other pollutants. But the real issue isn't where the stuff comes from—it's the rain that washes it out of the sky. Even as global rainfall is expected to increase, Allen, Landuyt, and Rumbold write, there's likely to be less frequent rainfall and, in some regions, less precipitation overall, resulting in higher aerosol concentrations.

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