The Hot Zone

A case for curbing near-term pollutants that worsen climate change

Posted by Alison Hawkes on February 22, 2011
Category : Climate Science and Scientists, The man made climate

Carbon dioxide is usually the greenhouse gas of choice in climate discussions, mainly because it’s long lasting, so the impacts of higher levels unfold over decades, if not centuries. But a new policy paper by the UNEP and World Meteorological Association shines light on the lesser discussed, more immediately potent molecules in the atmosphere: black carbon, and ground-level ozone.

The paper states that if reduction measures were introduced on these other molecules (by 2030), future global warming could drop by nearly 1 degree Fahrenheit, enough to cut in half the potential increase in global warming by 2050.

These companion molecules are emitted in the same way that CO2 gets into the atmosphere: combustion of fossil fuels. Black carbon is a heavy particle, the result of incomplete combustion of a fossil fuel or biomass like wood, that gets into the atmosphere and warms it by absorbing visible sunlight. Ground level ozone, O3, is a pollutant that is a major component of urban smog and is the result of a combination of pollution sources, including methane.

Black carbon levels are largely staying stagnant, the result of tighter standards on road transport and increased energy efficiency. But ground level ozone is increasing as economies continue to expand and burn more fossil fuels.

The report argues in favor of addressing the drivers of near-term warming, saying that many of the irreversible changes that are happening as climate change ramps up — including Arctic ice melt and release of methane and CO2 from permafrost — are near-term events. “Reducing the near-term rate of warming hence decreases the risk of irreversible transitions that could influence the global climate system for centuries.”

Staying within “critical temperature thresholds,” of less than a 3.6 degree Fahrenheit increase above pre-industrial levels, could be achieved with a reduction in black carbon and ground-level ozone. Both also have a very localized effect. Black carbon settles out onto snow and ice, creating a darker surface area that absorbs sunlight and exacerbates melt. Reducing black carbon emissions from local sources can give an added bump to the effectiveness of overall reduction measures. Ground-level ozone is a major health hazard, so reducing the compounds that lead to its formation would help improve air conditions for plants (including crops), animals, and humans.

The report outlines 16 ways to reduce these emissions. Among them, capturing methane releases from landfills, livestock manure, and refinery flaring, in the case of ground level ozone. For black carbon, it means installing particle filters on diesel engines and improving cooking methods in developing countries away from dirty stoves.

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