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Science Surveyblack carbon:a key cause of warmingnot well recognizedBy CHERYL HOGUEWarming Effect of Various PollutantsRadiative ForcingQuick – after carbon dioxide, what’s thesecond largest contributor to human-inducedglobal warming?It’s not methane from giant manure pitsand rice paddies.It’s not even a gas. It’s a solid.It’s black carbon, a type of particulatepollution. Scientists say black carbon is amajor cause of warming in the Arctic and theHimalayas.Black carbon didn’t figure prominentlyin the Intergovernmental Panel on ClimateChange’s landmark 2007 scientific assessmentof global warming. But research sincethen, especially a 2008 paper published inNature Geoscience, has boosted blackcarbon’s significance among the emissionsthat cause warming.Policymakers are increasingly interestedin black carbon these days because reducingemissions of it could curb global warming inthe short term. This could buy time for the developmentand deployment of new technologiesto reduce carbon dioxide releases over the long haul. However,black carbon is not among the emissions targeted for control underthe United Nations treaty to combat climate change.Black carbon comes from incomplete combustion. Sourcesinclude forest fires and the burning of diesel, coal, crop residues,wood, dung, or other biomass that people use for heating and cooking.It’s a constituent of fine particulate matter, a type of air pollutionlinked to respiratory and cardiovascular problems.JOURNALISTS, TAKE NOTE: BLACK CARBONISN’T CARBON BLACK.1.81.61.41.210.80.60.40.20A commercial product used as a pigment in inks and car tires,carbon black is also starting material for many products ofnanotechnology. There are key chemical and physical differencesbetween the intentionally produced commercial material and the1.66C02Black Carbon10 SEJournal Spring 20090.90.48CH4Halocarbons0.34 0.3Net Ozone0.16GREEN BARS INDICATE IPCC ESTIMATES; PURPLE SEGMENT INDICATES FINDINGS OF RECENTRESEARCH . UNITS ARE RADIATIVE FORCINGS, A MEASURE OF INFLUENCE ON GLOBAL ENERGYEXCHANGE, EXPRESSED IN WATTS PER SQUARE METER. SOURCE: EARTH TRENDS 2008, USINGDATA FROM IPCC 2007.widespread pollutant, according to the International Carbon BlackAssociation, an industry-sponsored group that conducts health,safety, and environmental research. The big difference, the associationsays, is that carbon black is generally composed of at least97% of carbon in its elemental form — meaning the atoms ofcarbon aren’t bonded with other elements.Black carbon, in contrast, has less elemental carbon than thecommercial product. It generally contains a fairly hefty amount ofother chemicals, including a family of hazardous air pollutantscalled polyaromatic hydrocarbons.Black carbon contributes to global warming in several ways.It absorbs the sun’s energy and heats up the air around it, just likea black dashboard and seats can make a car’s interior stifling on acool, sunny day.When wind currents sweep black carbon bits high into theatmosphere above most clouds — at an altitude of about 6,500 feetN20