WASHINGTON: Soot is the second-biggest human contributor to global warming behind carbon dioxide, and its impact on climate change has until now been sharply underestimated, a new study has revealed.

In the study published Tuesday in the Journal of Geophysical Research: Atmospheres, researchers admit that the uncertainties on the impact of soot are "substantial" -- meaning it could be an even greater threat than estimated.

The new estimate of the environmental impact of soot, which is based on new computer models, is double that put forth in 2007 by the Intergovernmental Panel on Climate Change, the UN's climate panel.

Soot, or black carbon, is generated by the incomplete combustion of oil, coal, wood or other fuels. Sources range from diesel engines to wood-burning stoves.

For the new study, scientists took into account the accumulation of soot in the atmosphere and the amount of solar heat that the particles absorb.

Soot only remains in the atmosphere for seven to 10 days, meaning that efforts to reduce the quantity of black carbon emissions could have a quick and dramatic impact on global warming.

In contrast, limiting global warming by reducing emissions of carbon dioxide is more of a long-term goal, given the accumulation of the greenhouse gas in the atmosphere, where it can remain for decades.

The uncertainties about the impact of soot are rooted in the fact that researchers do not fully understand how black carbon interacts with clouds.

Soot is a main target of the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants -- a multinational initiative backed by the United States, Canada and Mexico, among others.

The soot study came on the same day that US scientists announced that global temperatures were above average for the 36th straight year in 2012. Last year was the ninth or 10th warmest on record, depending on the measurement.