Going Beyond Carbon Dioxide - NYTimes.com 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. These reductions in methane, carbon monoxide and volatile organic compounds would also significantly reduce lower-level ozone, which is another important climate-warming pollutant that is formed by the interaction of sunlight with other short-lived pollutants. And HFCs, which are widely used in refrigerators, can be replaced with readily available climate-friendly refrigerants. Nearly 100 ozone-depleting chemicals have been phased out under the Montreal Protocol, an international treaty that took effect in 1989, and more than 100 countries support a shift to the safer HFC alternatives. Phasing down HFCs would provide climate protection many times greater than the current Kyoto climate treaty - the equivalent of about 100 billion tons of carbon dioxide by 2050. Many of these actions would improve public health and crop yields in the countries making the reductions, and perhaps encourage them to go further. The Obama administration began an important effort to reduce these pollutants when Secretary of State Hillary Rodham Clinton began the global Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants earlier this year. Twenty-five countries are now participating, along with the World Bank, the European Commission, the United Nations" environment and development programs and several environmental organizations. To achieve global scale, the coalition must find ways to work with large developing economies, including those of China, India and Brazil. Reducing short-lived climate pollutants is essential for slowing the pace of climate change in the near term. We can't forget about carbon dioxide. But this strategy would provide Mr. Obama the opportunity to show leadership at home by using his executive authority, and abroad by encouraging other countries to reduce these pollutants. His commitment could produce fast results and create a sense of urgent optimism that we need to solve the climate threat. Durwood J. Zaelke is the founder of the Institute for Governance and Sustainable Development. Veerabhadran Ramanathan is a professor of atmospheric and climate sciences at the Scripps Institution of Oceanography at the University of California, San Diego.