The tiny black particles released into the atmosphere by burning fuels are far more powerful agents of global warming than had previously been estimated, some of the world’s most prominent atmospheric scientists reported in a study issued on Tuesday.

These particles, which are known as black carbon and are the major component of soot, are the second most important contributor to global warming, behind only carbon dioxide, wrote the 31 authors of the study, published online by The Journal of Geophysical Research-Atmospheres.

The new estimate of black carbon’s heat-trapping power is about double the one made in the last major report by the United Nations’ Intergovernmental Panel on Climate Change, in 2007. And the researchers said that if indirect warming effects of the particles are factored in, they may be trapping heat at almost three times the previously estimated rate.

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Although some scientists have long believed that black carbon is a major force in climate change, the vast majority of previous mathematical models had predicted that the particles had only a modest impact. That view should now change, said Mark Z. Jacobson, an atmospheric scientist at Stanford University and one of the study’s authors, calling the old models “overly simplistic.” He said that many of his co-authors had previously hewed to the lower estimates.

Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption, influence on liquid, mixed-phase, and ice clouds, and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related; namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr-1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models, and should be increased by a factor of almost three. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71?W?m-2 with 90% uncertainty bounds of (+0.08, +1.27) W?m-2. Total direct forcing by all black carbon sources, without subtracting the pre-industrial background, is estimated as +0.88 (+0.17, +1.48) W?m-2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1?W?m-2 with 90% uncertainty bounds of +0.17 to +2.1?W?m-2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1?W?m-2, is the second most important human emission in terms of its climate-forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing.