What’s Soot Got To Do With It?

By Andrew Freedman

Most of the discussion regarding the highly anticipated Senate energy and climate change legislation, which Senators John Kerry (D-Mass.) and Joseph Lieberman (I-Conn.) introduced last week following months of negotiations, has focused on the bill’s provisions pertaining to offshore oil and gas drilling, incentives for renewable energy, and cap on carbon emissions for certain economic sectors.

Although the bill’s carbon dioxide (CO2) emissions reduction targets – an 80 percent emissions cut by 2050 compared to 2005 levels – would yield significant long-term climate benefits, the bill also addresses manmade climate change in the shorter term.

A little-noticed portion of the bill concerns short-lived air pollutants such as black carbon (otherwise known as soot) and tropospheric ozone. These pollutants disrupt the climate on far shorter timescales than CO2, which is the most important greenhouse gas and the main villain in the climate change story.

Once emitted by the burning of fossil fuels, the use of solid fuel cooking stoves or biomass burning, among other sources, black carbon only stays aloft for days to a few weeks before being washed out of the atmosphere by precipitation. This means that once black carbon emissions are reduced, there would be almost immediate climate benefits.

The Kerry-Lieberman bill would direct the US EPA to use its existing authority under the Clean Air Act to reduce black carbon emissions from diesel engines, using devices called diesel particulate filters which trap soot emissions before they escape via a vehicle’s tailpipe.

It would also call upon the EPA to publish a report on black carbon “sources, impacts, and reduction opportunities,” including an examination of how foreign assistance programs could help reduce emissions in other nations. In addition, the bill would establish an interagency process to facilitate “fast mitigation strategies” that focus on non-CO2 warming agents. This process would involve agencies such as the EPA and the Energy Department.

How big a climate player is black carbon?

Black carbon is thought to be a powerful warming agent in many regions, particularly snow and ice-covered areas such as the Himalayas and the Arctic. As its name suggests, black carbon particles are dark in color, and are therefore strong absorbers of incoming solar radiation. They warm the atmosphere and alter cloud characteristics, and when they land on brightly colored snow and ice, they darken the surface, causing a large uptick in the absorption of solar radiation, which hastens melting.

In the Arctic, black carbon contributes to a feedback loop that has helped cause a rapid melting of sea ice cover and drive temperatures upward at nearly twice the rate of the rest of the world. The decade from 1999-2008 was the warmest ten-year period in the Arctic of the past 2,000 years, according to a study published in the journal Science in 2009.

In addition to Arctic warming, black carbon has been shown to alter regional climate patterns such as the Indian monsoon, and human inhalation of soot particles is known to be a major health hazard worldwide.

In recent years numerous scientists, most prominently V. (Ram) Ramanathan of the Scripps Institution of Oceanography and James Hansen of NASA have called for significant cuts in short-lived air pollutants as a way to reduce climate change in the near term, while efforts continue to address CO2 emissions in the long run. Ramanathan’s studies have shown that black carbon may be the second largest contributor to global climate change.

In March testimony before the House Select Committee for Energy Independence and Global Warming, Ramanathan stated that the current global warming effect of black carbon “may be as much as 60 percent” of the CO2 warming effect. He noted, however, that there are significant uncertainties about black carbon’s role in the climate system.

Ramanathan told House lawmakers that reducing black carbon emissions “may provide a possible mechanism for buying time to develop and implement effective steps for reducing CO2 emissions.”

Bill is aligned with recent scientific advice

The Kerry-Lieberman bill’s inclusion of rapid mitigation strategies is consistent with advice contained in a new paper from an interdisciplinary panel of scholars, published on May 11 by the University of Oxford in the UK. The paper argues that non-CO2 drivers of climate change have been overlooked “for reasons of convenience in framing policy” rather than due to scientific concerns, and it presents a vision for an overhaul of climate policy that would include a much more prominent role for addressing emissions of short-lived air pollutants.

“Since action on these non CO2 ‘forcers’ may have quicker impact and large, immediate primary benefits, we would give them priority, now. In contrast to long and arduous tasks, these can be ‘quick hits’,” the report states.

The bill’s provisions are also consistent with the findings of a scientific panel that examined options to address rapid Arctic climate change. In a 2008 report, the panel strongly endorsed pursuing emissions reductions of black carbon and other short-lived air pollutants. “…Curbing short-lived climate forcing agents, through rapid international action and Arctic nation leadership, may prove to be the best and perhaps only viable strategy for slowing Arctic warming in the time frame of years to a decade,” the report stated.

Considering that the Kerry-Lieberman bill itself faces a highly uncertain future, with significant resistance in both political parties, it may yet take even longer to address what many experts consider to be a ripe, low hanging fruit of the climate challenge. This does not bode well, given that much more difficult work lies ahead in order to reduce CO2 and other longer lasting greenhouse gases.