Although carbon dioxide mitigation remains the principal climate target, new understanding is emerging about so-called short-lived climate forcers including black carbon (soot), tropospheric ozone, and methane. Tackling these short-lived climate forcers, scientists now argue, could lead to quickly won benefits ranging from slowing the Arctic ice thaw to improved air quality leading to better health, particularly in developing countries.
The exciting potential of short-lived climate forcers is largely due to their shorter lifespan in the atmosphere compared to long-lived substances such as carbon dioxide (CO2). As IIASA’s Dr. Markus Amann explains: “To solve climate change in the long term we need to reduce the amount of carbon dioxide emitted to the atmosphere. However, CO2 emissions stay in the atmosphere for over a hundred years. Much of the global warming that will occur in the next few decades is determined from CO2 already in the air. In reality there will be a substantial time lag between measures the world takes today to cut CO2 and their impact on global warming.”
To achieve more rapid results on near-term climate change, particularly at the regional level, IIASA scientists are now eyeing increased control of short-lived warming emissions (see “Non-CO2 greenhouse gas emissions in the EU,” left). This, it appears, is one of the few options to prevent irreversible damage to sensitive ecosystems and changes in rainfall patterns in the near term.
Black carbon (or soot), methane, and tropospheric ozone reside for much less time in the atmosphere than CO2 yet exert significant warming effects at the regional scale. For example, black carbon emissions—from diesel engines, cooking stoves, wood burning, and forest fires—are now believed to be responsible for around a quarter of recent warming in the Arctic (see “Tackling black carbon in the Arctic” below).
When suspended in air and deposited on snow, black carbon absorbs sunlight, which warms the air and can accelerate the melting of ice in polar and mountainous regions. Recent research also suggests that black carbon affects the weather through its impact on regional cloud formation and precipitation patterns.
Although black carbon lasts only up to a few weeks in the atmosphere, its warming potential is about 700 times greater than CO2 during the 100 years following emission. Methane, with its warming effects around 25 times greater than CO2, has an atmospheric lifetime of only 10–12 years. Such substances also lead to considerable damage to human health, agricultural crops, forests, and natural ecosystems. And, while these pollutants are often the subject of local air pollution control policies, assessing their impact on near-term climate change has to date been largely neglected.
Recently, IIASA scientists have extended IIASA’s GAINS (Greenhouse gas—Air pollution interactions and synergies) model to include emissions of short-lived gases and air pollutants. GAINS is an interactive, scenario-generating tool that allows users to identify the best strategies for simultaneously reducing air pollution and greenhouse gas (GHG) emissions. As some short-lived gases cool while others warm the atmosphere, the key to GAINS is its ability to take into account the combined impact of a mitigation measure on a range of gases.
Reducing the impact of short-lived pollutants. The left column illustrates the long term impact from the 2030 emissions of short-lived pollutants on radiative forcing, a key driver of temperature increases. The other columns demonstrate the potential to minimize the impact by applying a range of measures.
Based on this model scientists identify some 15 practical measures that, together, could reduce the global warming potential from short-lived pollutants by up to 60 percent compared to a baseline projection. All the measures are technically feasible and have been tried and tested.
The 15 measures include 12 technical measures aimed at reducing methane and black carbon emissions, such as the extended recovery of coal mine gas, the wide-scale introduction of pellet stoves and boilers in the residential sector, replacing traditional coke ovens with modern recovery ovens, and installing particle filters on diesel engines. The three non-technical measures are the elimination of biomass cook stoves in developing countries, the ban of open burning of agricultural waste, and enforcing existing legislation to eliminate high-emitting diesel vehicles.
“If these 15 measures were aggressively implemented by 2030, they could reduce global methane emissions by up to 45 per cent, black carbon emissions by some 70 per cent, and carbon monoxide emissions by 55 per cent below our baseline projections,” Dr. Amann explains. “The range of potential benefits includes increased human wellbeing from reduced local air pollution, better local environmental quality, reduced near-term climate change at the local and regional scale, increased security in food and energy supply, and lower water demand. In many cases, these measures would also result in more efficient energy use and thereby also reduce emissions of long-lived greenhouse gases,” he concludes.
Further information: A list of sources can be found online at www.iiasa.ac.at/Options/sources
Emissions from non-CO2 greenhouse gases such as methane and nitrous oxide in the EU will decline by 2030, according to a recent IIASA report to the European Commission. Based on the most recent projections of population and economic development, it is estimated that baseline emissions of non-CO2 GHGs will decline by 14 percent between 2005 and 2030. The primary reasons for this decline include the full implementation of the EU Landfill Directive, the declining number of dairy cows and non-dairy cattle following productivity increases in agriculture, and a decline in coal mining. Analysis further suggests that non-CO2 GHG emissions from non-ETS (European Emission Trading System) sectors by 2030 can be reduced by up to 41 percent below the 2005 level through full application of currently available technical mitigation measures.
Further information: Höglund-Isaksson L, Winiwarter W, Wagner F, Klimont Z, Amann M (2010). Potentials and costs for mitigation of non-CO2 greenhouse gas emissions in the European Union until 2030. Report to the European Commission, DG Climate Action. IIASA.
Black carbon from engines and forest fires is collecting in the Arctic where it is creating a haze of pollution that absorbs sunlight and warms the air. It is also being deposited on snow, darkening its surface and reducing the snow’s ability to reflect heat back into space. Recent studies suggest that this “soot” has been responsible for around a quarter of the total temperature increases in the Arctic between 1890 and 2007. The Arctic continues to warm more rapidly than almost all other parts of the globe.
Climate processes unique to the Arctic have significant effects that extend globally. The International Panel on Climate Change (IPCC) noted nearly 10 years ago that changes, which include melting of glaciers, sea ice, and permafrost, are already taking place. The consequences include disrupted wildlife migration patterns, altered fish stocks, modified agricultural zones, and increased forest fires. Consequently, as the 2010 Report by the Ad Hoc Expert Group on Black Carbon for the United Nations Economic Commission for Europe suggests, action must be taken in the very near term to reduce the rate of warming in the Arctic in comparison to other areas of the globe.
The 2010 Report argues that while there is no scientific consensus on the overall global climate effect of black carbon, consensus is nevertheless emerging regarding the regional influence of black carbon on areas of snow and ice. For the Arctic, scientists suggest, constraining the length of the ice melt season and, in particular, delaying the onset of spring melt, may best be achieved by targeting shorter-lived climate forcing agents such as black carbon. The benefit of these emission reductions will be felt much more quickly than reductions of long-lived greenhouse gases.
Further information: Ad Hoc Expert Group on Black Carbon (including IIASA’s Dr. Markus Amman, Dr. Kaarle Kupiainen, & Mr. Zbigniew Klimont) (2010). Black Carbon. Report to the Executive Body for the United Nations Economic Commission for Europe’s Convention on Long-range Transboundary Air Pollution.
Last edited: 28 August 2012
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