Going Beyond Carbon Dioxide

WE all know (or should know) by now that the carbon dioxide we produce when we burn fossil fuels and cut down forests is the planet’s single largest contributor to global warming. It persists in the atmosphere for centuries. Reducing these emissions by as much as half by 2050 is essential to avoid disastrous consequences by the end of this century, and we must begin immediately.

But this is a herculean undertaking, both technically and politically, as the lack of progress at United Nations climate talks here this week attests. And even if we are able to do this over the next 40 years, we would not slow the rate of warming enough by midcentury to moderate consequences like rising sea levels, the release of methane and carbon dioxide from melting arctic permafrost, and a rise in extreme weather.

There is, however, a short-term strategy. We can slow this warming quickly by cutting emissions of four other climate pollutants: black carbon, a component of soot; methane, the main component of natural gas; lower-level ozone, a main ingredient of urban smog; and hydrofluorocarbons, or HFCs, which are used as coolants. They account for as much as 40 percent of current warming.

Unlike carbon dioxide, these pollutants are short-lived in the atmosphere. If we stop emitting them, they will disappear in a matter of weeks to a few decades. We have technologies to do this, and, in many cases, laws and institutions to support these cuts. Moreover, President Obama has the executive authority to move ahead aggressively on these pollutants, as he did last year in ordering substantial reductions in auto and truck emissions. By doing so, he may persuade other countries to follow.

Such reductions, if they occurred worldwide, would have the potential to slash the rate of global warming by half by midcentury — equivalent to wiping out the warming we have experienced over the last 50 years. These reductions would also prevent an estimated two to four million deaths from air pollution and avoid billions of dollars of crop loss annually, according to a study commissioned by the United Nations Environment Program and the World Meteorological Organization.

We can reduce black carbon emissions significantly in the next few decades by using particulate filters on cars and trucks and switching to low-sulfur diesel. By employing those strategies, California, for instance, has cut the warming effect from diesel emissions by nearly half since the late 1980s.

In addition, we can further reduce emissions of black carbon and carbon monoxide (which produces lower-level ozone) in the developing world simply by turning to efficient biomass cook stoves instead of using traditional mud stoves, by replacing kerosene lamps in villages with solar lamps, and by deploying modern brick kilns.

Methane emissions can be cut by nearly a third by reducing leaks from gas pipes, coal mines and hydraulic fracturing, by capturing methane from waste dumps, water treatment plants and manure, and by cutting emissions from rice paddies.



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