SAN FRANCISCO—The quickest way to curb Arctic melting now underway may be to turn off the tap of short-lived pollutants swirling north from cities and industry far to the south, say scientists at the U.S. National Oceanic and Atmospheric Administration.
Preliminary data suggest that these pollutants can increase Arctic surface temperatures as much as 3 degrees Celsius—an effect equal to what scientists expect from carbon dioxide (CO2) and other greenhouse gases. But unlike carbon dioxide, these pollutants accumulate seasonally and dissipate far more quickly than CO2, suggesting that reducing these emissions represents one of the best hopes for staving off further unprecedented retreats of Arctic sea ice.
"At least it gives us something that we have a chance to mitigate, as opposed to something like [CO2], which has a much longer time scale given the rapid changes in the Arctic," said Patricia Quinn, an atmospheric chemist at NOAA's Pacific Marine Environmental Laboratory.
These pollutants include hydrocarbons like solvents and benzene, nitrogen oxides from motor vehicles and power plants, sulfates from coal-fired power plants and soot from industry and agriculture. They are the scourge of urban areas, contributing to asthma and other health problems. But in the Arctic, their effects are profoundly magnified—particularly for soot, or black carbon, Quinn said.
"There's a huge temperature inversion in the Arctic during the winter," Quinn said. "You don't get much vertical mixing, and you don't get much precipitation, so stuff that gets in there just sits. It can be in there for weeks."
The Arctic winter extends pollution's lifetime. In sunnier, more temperate regions, nitrogen oxides and hydrocarbons readily combine to form ground-level ozone, or smog—a greenhouse gas. But sunlight both builds and destroys, and in those regions the compounds are short-lived, lasting for days or even hours. In contrast, the dark of the Arctic winter acts like an ice chest, storing and preserving pollutants as they gradually accumulate over the season.
When the sun returns in the spring, several things happen at once, all to the detriment of the Arctic in particular and the global climate in general, researchers say.
* The sun bakes the accumulated ozone precursors into climate-warming smog. "You have all the precursors sitting there, and then when the sun comes up, you have all these ingredients for ozone," Quinn said. "And because it's dark, you can get ozone transported up there without it being destroyed."
* Particulate pollutants—also called aerosols—accumulate in and form clouds and haze, enhancing the clouds' ability to insulate and increasing surface warming.
* The atmosphere starts to mix again and precipitation returns, washing black carbon, or soot, from the air. It lands on the icepack just as the ice is starting to melt and creates a devastating feedback loop, Quinn said. "If you're now taking the ice and covering it with something black, it accelerates (the melting) even further."
Other than smelters in northern Russia and an increasing shipping presence, the Arctic has very few sources of localized industrial pollution. Most pollution gets carried north by air currents from sources in urban centers across North America, Asia and Europe. The net result, said John Burkhart, a scientist at the Norwegian Institute for Air Research, is that "the Arctic is poised to be as polluted as other places."
The effect, researchers say, is comparable to that of carbon dioxide and other greenhouse gases combined. Preliminary data presented at the American Geophysical Union Fall Meeting last month indicates short-lived pollutants have increased Arctic surface temperatures up to 3 degrees C in winter.
So while reducing CO2 remains a vital part of any global warming mitigation strategy, inertia and political hurdles associated with CO2 have experts suggesting that the fastest way to put the brakes on Arctic warming is to curb emissions of short-lived pollutants far to the south.
Furthermore, researchers say, CO2's long lifespan and inertia means even an immediate and substantial reduction in CO2 emissions will take years to alter Arctic warming trends. Yet the same reduction in short-lived pollutants, they note, could substantially reduce Arctic warming now - and bring numerous health benefits to people throughout the Northern Hemisphere.
"We have very little leverage to affect the effects of CO2," said Drew Shindell of NASA's Goddard Institute for Space Studies. "This is not so for short-lived pollutants."
Elizabeth Grossman is a Portland-based writer and author, most recently, of "High Tech Trash: Digital Devices, Hidden Toxics, and Human Health."