The Menace of Clean Air: CLEANER AIR MAY SPEED GLOBAL WARMING, the New York Times headlined last week. Huh? The apparently nutty story reports the British technical journal Nature contains a study showing that air pollution prevents global warming; with air pollution declining markedly in Western nations at least, global warming would be expected to accelerate. Actually this is quite logical. Air pollution contains soot and other tiny dark particles that hang in the air and reflect sunlight back into space. As air pollution declines and the sky becomes clearer, more sunlight reaches the ground. This suggests polluted sky would tend to cool the Earth, while clean sky would tend to allow warming. So maybe it's not such a mystery why global mean temperatures declined in the first half of the 20th century, then rose in the second half. In the first half of the 20th century, thick, dark smoke pollution from unregulated coal-burning was ubitquitous in Western nations -- London's killer smog of 1952 killed several thousand people, while a blanket of coal-burning smog killed 21 people in Dorona, Pennsylvania, in 1948. Significant areas of the planet were shrouded in pollution-caused clouds during the first half of the last century, and these clouds reflected away sunlight.So what if it did come from an article about football? It's good stuff.
Decades of ever-more-complex pollution-control mechanisms on power plants, vehicles and industrial facilities have eliminated smoke pollution in the Western world, though this scourge continues in China and India, while greatly reducing fine soot. All forms of air pollution have declined dramatically in the United States: Overall air pollution is down 36 percent in the last 15 years alone, despite big increases in population, economic output and energy use. And despite the commonly heard political claim that George W. Bush has "rolled back" or in some way softened the Clean Air Act -- it's the reverse, Bush has issued a series of rulings making the Clean Air Act more strict -- air pollution has continued its trend of decline during the Bush presidency. (Links to the relevant trend studies are here.)
So the air is getting cleaner, which will accelerate global warming. Clean air -- it's hazardous! Talk about postmodern concepts. The new study didn't surprise me because 16 years ago yours truly wrote, for the Los Angeles Times, an article warning about such zany interaction of pollutants. My 1989 article noted that declining air pollution would be expected to accelerate global warming. I also noted that one reason ultraviolet radiation from stratospheric ozone depletion never caused the predicted harm is that ground-level ozone in urban smog reflected away the UV rays. But watch out, I wrote in 1989: "This means it's only safe to sunbathe in a smoggy location such as Los Angeles, not in some dangerously clean place like Hawaii." Today that zany equilibrium has shifted. Los Angeles air quality has improved very dramatically -- just one stage-one ozone alert in Los Angeles in the last six years, versus 100 or so per year during the 1970s -- while stratospheric ozone depletion is no longer a threat owing to the ban on CFCs. Anyway it sounds weird, but the fact that air quality keeps improving really is one of the reasons climate change is becoming more of a concern.
Skin cancer isn't only for Hawaii anymore!
Nature note: This journal is generally considered the world's number-two hard-science publication, following the American journal Science. Surely Nature yields to no one when it comes to dense-ness -- the current issue contains, for example, a paper titled "Genomic Sequence of the Pathogenic and Allergenic Filamentous Fungus Aspergillus Fumigatus ." (The paper lists 98 authors.) Yet Nature also offers podcasts http://www.nature.com/nature/podcast/index.html. You might want to download the Christmas special podcast: "Why dancing and sex go hand-in-hand, how reindeer beat winter blues, pursuing the star of Bethlehem, wines that rock and saving the spirit of tequila."
And if you were wondering about my comment concerning global warming from above. Every single thing you do causes global warming. In fact, every action that happens on the planet causes global warming as well. It has to do with the principal of enthropy. All energy eventually becomes heat, and every time we use energy, to work on a computer, to move our legs, we are causing more heat. So there.