Reducing soot emissions to slow the rapid melting of Arctic sea ice
According to a new study by Stanford researcher Mark Z. Jacobson, the quickest and best way to slow the rapid melting of Arctic sea ice is to reduce soot emissions from the burning of fossil fuel, wood and dung. Jacobson said, “There is a big concern that if the Arctic melts, it will be a tipping point for the Earth’s climate because the reflective sea ice will be replaced by a much darker, heat absorbing, ocean below. Once the sea ice is gone, it is really hard to regenerate because there is not an efficient mechanism to cool the ocean down in the short term.”
In his study Jacobson used an intricate computer model of global climate, air pollution and weather that he developed over the last 20 years that included atmospheric processes not incorporated in previous models. He examined the effects of soot – black and brown particles that absorb solar radiation – from two types of sources. He analyzed the impacts of soot from fossil fuels – diesel, coal, gasoline, jet fuel – and from solid biofuels, such as wood, manure, dung, and other solid biomass used for home heating and cooking in many locations. He also focused in detail on the effects of soot on heating clouds, snow and ice.
Jacobson found that eliminating soot produced by the burning of fossil fuel and solid biofuel could reduce warming above parts of the Arctic Circle in the next 15 years by up to 1.7 degrees Celsius. This is quite significant when compared to the fact that the net warming in the Arctic has been at least 2.5 degrees Celsius during the last century and is expected to warm significantly more in the future if nothing is done.
Jacobson also found that although fossil fuel soot contributed more to global warming, biofuel-derived soot caused about eight times the number of deaths as fossil fuel soot. He found that soot emissions kill more than 1.5 million people prematurely worldwide each year, and afflicts millions more with respiratory illness, cardiovascular disease and asthma, mostly in the developing world where biofuels are used for home heating and cooking. Providing electricity to rural developing areas, thereby reducing usage of solid biofuels for home heating and cooking, would have major health benefits, he said.
Jacobson’s climate model is the first global model to use mathematical equations to describe the physical and chemical interactions of soot particles in cloud droplets in the atmosphere. This allowed him to include details such as light bouncing around inside clouds and within cloud drops, which he said are critical for understanding the full effect of black carbon on heating the atmosphere.
“The key to modeling the climate effects of soot is to account for all of its effects on clouds, sea ice, snow and atmospheric heating,” Jacobson said. Because of the complexity of the processes, he said it is not a surprise that previous models have not correctly treated the physical interactions required to simulate cloud, snow, and atmospheric heating by soot. “But without treating these processes, no model can give the correct answer with respect to soot’s effects,” he said. Jacobson argues that leaving out this scale of detail in other models has led many scientists and policy makers to undervalue the role of black carbon as a warming agent.
Jacobson is a professor of civil and environmental engineering and a senior fellow at Stanford’s Woods Institute for the Environment.
Source: http://news.stanford.edu/news/2010/july/soot-emissions-ice-072810.html
July 29, 2010