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Environment

The Low Hanging Climate Pollutant

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In the zero-sum climate change debate, there's not much political space to discuss stopgap measures that would go a long way towards addressing climate change now. Take the issue of black carbon (also known as black soot), a noxious pollutant in developing countries that emanates from inefficient cooking stoves. Here's a revelatory passage from a 2009 NYT story by Elisabeth Rosenthal:

While carbon dioxide may be the No. 1 contributor to rising global temperatures, scientists say, black carbon has emerged as an important No. 2, with recent studies estimating that it is responsible for 18 percent of the planet's warming, compared with 40 percent for carbon dioxide. Decreasing black carbon emissions would be a relatively cheap way to significantly rein in global warming "” especially in the short term, climate experts say. Replacing primitive cooking stoves with modern versions that emit far less soot could provide a much-needed stopgap, while nations struggle with the more difficult task of enacting programs and developing technologies to curb carbon dioxide emissions from fossil fuels.

In the Hartwell Paper, which I first discussed earlier this week, the authors suggest prioritizing action on "non-CO2 forcing agents," such as black carbon. The paper argues that addressing this significant (though under-discussed) pollutant can 1) help build necessary political traction for climate policy, 2) vastly improve public health and 3) substantially reduce greenhouse gases in the short-term. Oddly, though, the paper doesn't offer any policy recommendations for eradication of black carbon emissions. So via email, I asked Hartwell co-author Atte Korhola, a professor of environmental change at the University of Helsinki, to elaborate on why we should take black carbon seriously in the climate debate, and to offer some concrete actions that can help reduce the harmful soot. Atte Korhola: Black carbon is a ubiquitous product of incomplete combustion, formed by natural forest fires, motor vehicles, coal plants and myriad other sources. According to current estimates diesel combustion and residential fuel use (from coal, wood and agricultural debris) each produce roughly one quarter of the total emissions of soot; another 40% comes from wildfires and controlled agricultural burning; various industrial sources make up the remainder. Soot contains both black carbon and light-colored particles that cool the planet. Smoke produced by sources such as cooking stoves and diesel engines tends to be rich in darker particles, so the pollution control focus should be on sources dominated by black carbon, such as residential combustion of solid fuels and high-emitting diesel engines, that have a stronger warming effect than others such as biomass burning, which is generally dominated by organic carbon. Reducing black-carbon emissions isn't really a technical problem "” modern stoves and filters can do most of the work "” so much as an issue of governance and resources. New combustion techniques and after-treatments often reduce particle emissions by several orders of magnitude in provision of the same service. Simply replacing solid fuels in home cooking stoves in developing countries with cleaner fuels and combustion technologies can lead to dramatic improvements in health and is eminently feasible. Actions may be fundable as part of general aid programs or under the UN Framework Convention on Climate Change (UNFCCC) Clean Development Mechanism (CDM). Much of the focus should be on developing countries. Governments should already be working to clean up diesel emissions and to improve cooking stoves especially in southeast Asia, where the health problems are most acute. But also industrialized nations could clean up fossil fuels further and reduce agricultural emissions at home. Emissions in the developed parts of the world are dominated by transportation sources such as heavy duty diesel trucks. Addressing BC emissions from public transport is likely to be a promising way to reduce climate interference. For example, some studies have reported that the fuel switching policy (e.g. to natural gas) resulted in a dramatic reduction in BC emissions from buses, e.g. in India. According to conservative estimates, one ton of black carbon causes about 600 times the warming of one ton of carbon dioxide over a period of 100 years. Unlike carbon dioxide, which stays in the atmosphere for centuries, black-carbon particles remain in the air for just a matter of weeks. So, in principle, efforts to eliminate emissions could quickly reduce the warming power of this pollutant. ***Postscript*** In April of 2009, a week after Rosenthal's NYT article on black carbon was published, there seemed to be some bi-partisan agreement on tackling the problem. More recently, though, the issue in the U.S. debate has become inextricably bundled with pending (and virtually paralyzed) congressional climate legislation. On this note, it bears mentioning that the Hartwell paper suggests we

need to separate the policy frameworks and interventions for attending to shortlived versus long-lived climate forcing agents.

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