Black Carbon

U.S. should act now to reduce short-lived pollutants damaging the climate

Last year’s extreme drought, wildfires and the devastation of Hurricane Sandy have driven home the high economic costs associated with extreme weather. The increasing frequency and intensity of such events make it clear that climate change presents a real and present danger. It no longer can be dismissed as a problem only of concern to our children or grandchildren.  

This increased urgency has also caused an important shift in our understanding of what actions are required to slow the rate of climate change. Recent studies have focused on the need for a two-pronged approach. Reducing emissions of carbon dioxide, some portion of which stays in the atmosphere for centuries, is critical to long-term efforts. But curbing greenhouse gases with shorter atmospheric lifetimes will have significant near-term climate and public health benefits.

How U.S. Can Lead on Short-Lived Climate Pollutants

With Secretary Clinton’s announcement this week of a new coalition aimed at short-lived climate pollutants such as methane and soot, the U.S. is helping to focus international attention on a critical but frequently overlooked dimension of the climate challenge. To maximize its leadership on this front, the U.S. should also take stronger steps to tackle these pollutants at home.

The new multilateral effort to address short-lived climate pollutants (also called short-lived climate forcers) is an important recognition of both the scientific and political realities that surround climate change. A growing body of scientific evidence underscores the importance of near-term action to slow the rate of climate change, which is proceeding more rapidly than scientists predicted. Because methane, black carbon and hydroflurorocarbons (HFCs) have relatively short atmospheric lifetimes, reductions in these compounds will have significant near-term benefits in reducing climate change.  In contrast, carbon dioxide remains in the atmosphere for hundreds of years. Reductions in CO2 are critical to limit the amount of warming over the longer term, but have more limited impact in the near term.   

The Other Carbon

Most development and analysis of climate change policies have focused on reducing carbon dioxide and other greenhouse gases (GHGs), which are widely recognized as the major contributors to climate change. And as we blogged about last year, far less attention has been given to black carbon (BC). However things may be changing. Inspired by University of California – San Diego professor Veerabhadran Ramanathan’s Foreign Affairs article, “The Other Climate Changers,” the United States House Select Committee on Energy Independence and Global Warming held a hearing last Tuesday to investigate the impacts of black carbon pollution. The takeaway message from this hearing is that BC policies should be complementary to efforts to reduce GHG gases. Reductions in emissions of black carbon would have near-term effects on reducing global warming that are not possible from actions directed at carbon dioxide and other long-lived gases. Reducing BC is good for the environment, public health, and creates jobs. We recently published a detailed primer on BC science and policy.

Both professors Ramanathan and Tami Bond of University of Illinois at Urbana-Champaign gave an overview of the science of black carbon – uncombusted materials like soot and smoke. A growing body of evidence indicates that soot and smoke are major contributors, possibly second only to carbon dioxide, to human-induced global warming. BC warms the air by absorbing sunlight in the atmosphere, changes rainfall patterns and, when deposited on snow and ice, accelerates melting. According to Professor Ramanathan, BC’s warming effect is around 40 to 70 percent of that of carbon dioxide. However, unlike carbon dioxide, black carbon does not accumulate in the atmosphere; it stays in the atmosphere for a few weeks, so the impacts are more concentrated in the areas where they are produced, and reducing BC emissions would have near-term benefits in those areas.

BC is produced by both natural processes and human activity from the incomplete combustion of fossil fuels, biofuels, and biomass. According to Professor Ramanthan, the regional effects of BC are particularly large over the Arctic, Africa, and Asia. BC leads to increased melting of snow and ice in the Arctic, Sahelian drought, and decreased monsoon rainfall. Primary sources include diesel engines, small industrial sources, residential coal and solid biofuels for cooking and heating, and agricultural and forest fires.

Since the impacts of BC are regional, there are significant local environment, public health, and economic benefits of reducing BC emissions. Reducing BC emissions in India for example, would not only produce environmental benefits of cleaner air and negate rainfall loss, but would also save lives. Professor Ramanathan’s calculations indicate that replacing cook stoves in India with advanced biomass stoves could prevent 2 million deaths from the reduction of particulate matter produced by traditional stoves. Mitigating BC emissions would also prevent reduced rainfall and reduced agriculture yields.

According to another panelist, Conrad Schneider, Advocacy Director of the Clean Air Task Force, reducing BC emissions can create clean jobs here in the United States. Even though BC isn’t much of a climate forcing in the U.S. and a potentially expensive source of reductions, there is a billion dollars worth of work to reduce diesel’s BC emissions. For example, retrofitting 11 million diesel engines in the U.S. today could achieve the same environmental benefit as removing 21 million cars from the road, would save approximately 7,500 lives through reduced particulate matter pollution, and create tens of thousands of domestic jobs.

In order to get the environmental, economic, and public health benefits of reduced BC emissions, all the witnesses agreed that action must be taken. For more information, please check our white paper on the climate impacts of black carbon.

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