Black Carbon and Climate

Today, the Obama Administration has formally recognized the importance of black carbon as a component of broader policies to address climate change. At the UN Climate Change Conference in Copenhagen, Nancy Sutley, the Chair of the Council on Environmental Quality, announced an initiative aimed at reducing emissions of black carbon. The United States is committing $5 million towards international cooperation to reduce black carbon emissions in and around the Arctic. According to Chair Sutley, the new initiative will include investments to study the effects of black carbon, demonstrate options for reducing emissions, and begin to quantify both the climate and public health benefits of reducing emissions. The initiative will focus on diesel engines (both on-road and non-road, including those used for port operations), older district heating and industrial facilities, and agricultural and forest fires.

We just released a new white paper highlighting the climate impacts of black carbon (Black Carbon: A Science/Policy Primer). Over the last decade, a growing body of evidence indicates that soot and smoke are major contributors to climate change. Black carbon, a component of soot, warms the air by absorbing sunlight in the atmosphere, changes rainfall patterns and, when deposited on snow and ice, accelerates melting. Black carbon is produced by both natural processes and human activity from the incomplete combustion of fossil fuels, biofuels, and biomass. Primary sources include diesel engines, small industrial sources, residential coal and solid biofuels for cooking and heating, and agricultural and forest fires.

The new paper summarizes current knowledge on the climate effects of soot components (black carbon and organic particles) and identifies emission sources and technologies to mitigate their impacts. It also presents perspectives on the potential role of soot mitigation approaches in developing more comprehensive climate strategies.

Black carbon remains in the atmosphere for only days to weeks, meaning it has strong regional climate effects. Recent studies suggest that black carbon may be responsible for 30-50 percent of recent warming in the Arctic, contributing to the acceleration of Arctic sea ice melting. Loss of Arctic sea ice is one potential “tipping point” that could lead to rapid warming and irreversible climate change. Black carbon is also driving increased melting of the glaciers in the Himalayan Plateau, upon which some 40 percent of the world’s population depends for fresh water. Reductions in black carbon would help address these issues and also would have many co-benefits, particularly in public health and especially in the developing world.

Controlling emissions of CO2 and long-lived greenhouse gases must remain the centerpiece of policies to address climate change, since they ultimately drive the Earth’s temperature in the long term. However, reducing black carbon emissions represents a win-win scenario: it would have an immediate cooling effect on the Earth’s climate, potentially delaying temperature increases in the short run and helping reduce the risk of irreversible tipping points in the climate system, and it would reduce air pollution, significantly improving public health.

Jeremy Richardson is Senior Fellow for Science Policy