Aerosols More Important to Global Warming Than Acknowledged
Increasing black carbon pollution from Asia can have a large global warming impact. Photo: Ginny via flickr
While the vast majority of climate change discussion has been the impact of greenhouse gases themselves (carbon dioxide, methane, others) on Earth's warming climate, the impact of aerosols has received less attention. And according to a new report, as aerosols may be driving a significant portion of polar warming, this is unfortunate:A study led by Drew Shindell of NASA's Goddard Institute for Space Studies says that, in the high latitudes the impact of aerosols (sulfates and black carbon) may account for 45% or more of the observed warming which has occurred in at the poles over the past three decades. Over that time Arctic temperatures have risen by 1.7°C, while Antarctic regions have witnessed 0.35°C temperature increases.
Black Carbon and Sulfates Have Opposite Global Warming Impact
The unevenness of temperature rises can be accounted for in the type of aerosols in the atmosphere:
Sulfates, which come from burning coal and can have a net cooling effect on the planet, have actually declined in the past 30 years. This is the result of laws being enacted in the US and Europe which have reduced sulfate emissions by 50%--a good thing in terms of air quality and public health, but not so much in terms of holding global warming due to increasing greenhouse gas emissions in check.
Black carbon, on the other hand, contributes to rise temperatures. These sooty particles are emitted by industrial activity and by the burning of diesel and biofuels. They absorb incoming radiation and contribute to warming; they're also on the rise, in large part because of increasing industrialization in Asia.
Reductions In Sulfates in US, Europe Have Accelerated Arctic Warming
The disparate effects at the poles makes sense,
...because of the Arctic's proximity to North America and Europe. The two highly industrialized regions have produced most of the world's aerosol emissions over the last century, and some of those aerosols drift northward and collect in the Arctic. Precipitation, which normally flushes aerosols out of the atmosphere, is minimal there, so the particles remain in the air longer and have a stronger impact than in other parts of the world.
Since decreasing amounts of sulfates and increasing amounts of black carbon both encourage warming, temperature increases can be especially rapid. The build-up of aerosols also triggers positive feedback cycles that further accelerate warming as snow and ice cover retreat.
In the Antarctic, in contrast, the impact of sulfates and black carbon is minimized because of the continent's isolation from major population centers and the emissions they produce.
In the end, Shindell said that,
We will have very little leverage over climate in the next couple of decades if we're just looking at carbon dioxide. If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we're much better off looking at aerosols and ozone.
via: Science Codex
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