Arctic sea ice is retreating at an unexpectedly rapid pace. Average ice extent in September has declined by 11.5 percent per decade relative to the 1979 to 2000 average, according to satellite measurements of the ice. Many climatologists expect that the Arctic will be ice-free during the summer in as few as thirty years if current trends continue.
Most scientists who study the issue closely agree that reducing carbon dioxide emissions is the key to stabilizing Earth’s climate. However, even if nations began curbing emissions immediately the world would continue to warm for many decades. While Earth can reabsorb some portion of carbon dioxide emissions fairly rapidly, a significant amount of carbon will remain in the atmosphere for long periods. Some 20 percent of carbon dioxide emissions are expected to remain in the atmosphere for tens of thousands of years, according to some estimates.
That doesn’t bode well for the dwindling Arctic sea ice.
However, if Mark Jacobson, an atmospheric scientist from Stanford University is right, there may still be hope for Arctic sea ice and the ecosystem it supports. Jacobson studies the climate effects of tiny airborne particles called black carbon, a scientific term for soot, the black stuff in smoke. Wood, dried animal dung, and other biofuels all produce black carbon when burned. And fossil fuels, such as coal and petroleum, are especially prolific producers of the particles.
Under a microscope, black carbon is an amorphously-shaped particle with a branching globular shape. What’s most notable about black carbon, however, is the many ways that it can warm the climate. Black carbon particles, which unsurprisingly tend to be a coal black color, warm the air directly by absorbing sunlight and converting it into infrared radiation. They also reduce the reflectivity of the surface when deposited on icy surfaces. And they infiltrate cloud droplets in ways that can cause clouds to dissipate more quickly than they otherwise might.
Together such effects can produce a potent warming effect. Last week, during a session focused on black carbon at the American Geophysical Union meeting in San Francisco, Jacobson reminded meeting attendees of a bit of news that Stanford released a few months back. Reducing soot emissions may be the fastest method – indeed the only way — of saving the Arctic ice, Jacobson noted. “On average black carbon particles stay in the air for just four or five days, so reducing emissions has an immediate impact,” he said in an interview later. “That’s not the case for greenhouse gases.”
Recent modeling, conducted by Jacobson and funded in-part by NASA, suggests that eliminating soot emissions from fossil fuel and biofuel burning over the next fifteen years could reduce Arctic warming by up to 1.7 °C (3 °F). Net warming in the Arctic, in comparison, has been about 2.5 °C (4.5 °F) over the last century.