• Curbing these 4 pollutants could slow sea level rise

    Andrew Kemp, Yale University

    Sea level rise is swamping coasts; Rodanthe in the Outer Banks of North Carolina is pictured.

    By Becky Oskin
    LiveScience

    Sharp reductions in short-lived airborne pollutants could significantly slow sea level rise before 2100, a new study finds.

    The four pollutants — black carbon, methane, ozone and hydrofluorocarbons — all cycle through the atmosphere more quickly than carbon dioxide, which lasts for centuries in the troposphere, the part of the atmosphere we live in and breathe. Carbon dioxide is the main culprit in Earth's warming temperatures, which impacts sea level rise both by the expansion of water as it warms and by the melting of glacial ice.

    Cutting the air pollutants, which all also act to trap heat in the atmosphere and last anywhere from a week to decade, worldwide by 30 percent to 60 percent over the next several decades would lower predicted sea level rise by 22 percent to 42 percent by 2100, according to the study, published Sunday in the journal Nature Climate Change.

    Sea levels are expected to rise between 7 inches to 6.6 feet (18 centimeters to 2 meters) this century, according to a 2007 assessment by the Intergovernmental Panel on Climate Change. The higher tides will bring more coastal flooding and bigger storm surges, the IPCC report warned.

    Though the four pollutants are known contributors to climate change, policymakers tend to focus on carbon dioxide, the 800-pound-gorilla of global warming, when it comes to reducing emissions. Frustrated at the slow pace of negotiations on cutting carbon dioxide, the research team decided to investigate other ways to slow the planet's warming, according to a statement from the National Center for Atmospheric Research (NCAR) in Boulder, which participated in the research.

    "To avoid potentially dangerous sea level rise, we could cut emissions of short-lived pollutants even if we cannot immediately cut carbon dioxide emissions," NCAR's Aixue Hu, lead study author, said in the statement. "This new research shows that society can significantly reduce the threat to coastal cities if it moves quickly on a handful of pollutants."

    The study models relied on emissions cuts beginning in 2015. Hu and his colleagues tested the effects of lowering atmospheric levels of the four gases and particles by 30 percent to 60 percent over the next several decades, the steepest cuts economists believed possible, the study said.

    Even if these cuts are made, though, carbon dioxide is still the main threat, the authors said.

    "It must be remembered that carbon dioxide is still the most important factor in sea level rise over the long term," Warren Washington, a study co-author at NCAR, said in the statement. "But we can make a real difference in the next several decades by reducing other emissions."

    Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook and Google+. Original article on LiveScience.com.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Surprising strategy to fight global warming: Cut down on soot

    EPA

    Scientists say cutting back on emissions from diesel engines could slow global warming quickly.

    By John Roach, NBC News

     A quick hit way to slow the pace of global warming may be to tackle soot emissions from things such as diesel cars and coal-burning cookstoves, according to a new study that finds the black carbon these devices emit is the second-biggest contributor to global climate change.

    All told, soot has about two-thirds the effect on warming as the best-known greenhouse gas, carbon dioxide. The findings push methane, which is emitted by everything from belching cattle to fracking operations, from the No. 2 spot.

    Soot, also known as black carbon, has an atmospheric half-life of just a few days, unlike the century-long staying power of carbon dioxide. That suggests that efforts to curb black-carbon emissions could have an immediate impact on warming.

    While the finding is no excuse to continue efforts to curb carbon dioxide emissions, "we have a potential for slowing warming by doing black carbon mitigation as well," Sarah Doherty, an atmospheric scientist at the University of Washington, told NBC News.

    Doherty is one of four lead authors of a four-year study that resulted in the 232-page report published Tuesday in the Journal of Geophysical Research – Atmospheres. The report provides a comprehensive assessment of black carbon’s climate impact.

    Even before they did their analysis, the researchers knew that soot probably played a significant role in the process of global warming. But they were surprised to find that black carbon's contribution is twice as large as reported by the Intergovernmental Panel on Climate Change in its 2007 assessment.

    "It was not the result that we expected," Doherty said.

    Black carbon affects the global climate through myriad mechanisms. It absorbs sunlight, leading to atmospheric warming. Particles of the stuff can change the properties of clouds, making them less reflective.

    Bond et al. / American Geophysical Union

    Schematic overview of the primary black carbon emission sources and the processes that control the distribution of black carbon in the atmosphere and determine its role in the climate system.

    "Then there is black carbon getting deposited on the snow and ice and making it darker so it absorbs more sunlight. It warms the surface of the earth, and it also produces earlier snowmelt," Doherty explained.

    The team accounted for all of these effects — as well as the fact that sources of black carbon such as burning forests also emit aerosols, which reflect sunlight and have a cooling effect. In other words, the emissions from some sources cancel each other out, at least over the short term.

    For anyone concerned with slowing climate change, the goal is to identify which sources of black carbon to target in order to gain the most bang for the buck. According to the analysis, those sources are "diesel engines and burning of wood and coal for domestic purposes, like for cooking," Doherty said.

    New standards in place in the U.S. and Europe have already ushered in clean-burning diesel cars and trucks. Rolling out the technology to the developing world could have a large impact on soot emissions. 

    Cleaner-burning cookstove technology is available as well. It becomes a matter of cultures being able to afford and willing to embrace the change, Doherty explained. Doing so also has a side benefit of improved health, which could strengthen the case for spending the money on programs to promote cleaner-burning stoves.

    But none of this, she stressed, should be approached at the expense of efforts to curb emissions of other greenhouse gases, notably carbon dioxide. She likens it to treating patients whose chronic boozing causes liver failure — and finding out they also eat fast food at every meal, which is also bad for the liver.

    "You would never say to them, 'Well, stop eating fast food, but you can keep on drinking for a while, and once you've gotten that fast food out of your system, then you can worry about cutting back on your drinking," she said. "You wouldn't do that."

    John Roach is a contributing writer for NBC News. To learn more about him, check out his website.