Cutting Black Carbon and Methane Promises Immediate Climate Change Impacts

Reducing emissions of black carbon and methane can be done today with existing technologies, and could significantly slow climate change

Feb 05, 2011 - Lauren Morello - ClimateWire - scientificamerican.com

CLIMATE CURB?: Cutting emissions of so-called black carbon--soot and other aerosols--as well as methane could stave off catastrophic climate change. Image: Courtesy of Visible Earth, NASA.gov

Placing strict limits on a handful of common air pollutants could pay big dividends for efforts to limit climate change, improve public health and increase agricultural productivity, according to a new U.N. report.

Curbing emissions of black carbon, a component of soot, along with methane and tropospheric ozone, could cut projected climate warming by 0.5 degree Celsius, or about 0.9 degrees Fahrenheit, by 2070.

Such cuts could be made with existing technology, the report says, and would "have immediate and multiple benefits for human well-being."

Possible strategies for reducing black carbon, methane and ozone include capturing methane produced by landfills and fossil fuel extraction, introducing cleaner-burning cookstoves, installing particulate filters on diesel engines and banning the practice of burning fields of agricultural waste.

The research shows that cutting black carbon and methane emissions would slow the rate of warming up until about 2040, while starting soon to cut emissions of carbon dioxide would only have an appreciable effect after 2040.

Drew Shindell, the scientist who coordinated the international team that wrote the new report, said that suggests that both approaches are needed.

"When you put them together, this is the only scenario when you have a reasonable fighting chance of staying below the 2 degree [Celsius] target," said Shindell, a climate researcher at NASA's Goddard Institute of Space Studies. "One targets the near term; one targets the long term."

Meanwhile, limiting emissions of black carbon and chemicals that react with sunlight to form tropospheric ozone could prevent 2.4 million premature deaths and the loss of 1 to 4 percent of the global output of maize, rice, soybean and wheat each year, the analysis found.

Looking for impetus from governments
Shindell and other researchers who worked on the new report presented their findings over the weekend at the annual meeting of the American Association for the Advancement of Science.

The study was supported by the U.N. Environment Programme, the World Meteorological Organization and the Stockholm Environment Institute. The analysis will be delivered tomorrow to the U.N. environment body's governing council at a meeting in Nairobi, Kenya.

"Hopefully, there will be some impetus there to move forward," said Ashbindu Singh, chief of UNEP's Division of Early Warning and Assessment. "UNEP on its own cannot do much unless the governments tell us what to do."

UNEP commissioned the study, originally asking researchers to examine the effect of cutting emissions of black carbon, a particle produced by burning fossil fuels and biofuels like wood and dung.

Shindell said researchers expanded the analysis to look at chemicals like methane and precursors to ozone because they are emitted by the same processes -- like biomass burning -- that produce black carbon.

Like black carbon, methane and ozone are potent -- albeit short-lived -- greenhouse warmers. Black carbon, for example, lingers in the atmosphere for weeks, compared to CO2, which can last for centuries to millennia.

All three can damage human health, while ozone can lower crop yields.

Meanwhile, black carbon acts in several ways to accelerate climate change. It absorbs heat from sunlight, warming the surrounding air. When particles of black carbon fall from the atmosphere on ice or snow, they hasten melting. Shindell's earlier work suggests that black carbon emissions caused half the total warming in the Arctic between 1890 and 2007.