California laws to clean up diesel vehicles over the last 20 years have managed to slash black carbon levels in half, according to new research.

Black carbon is caused by diesel engines, cooking stoves, forest fires and the burning of fossil fuels. The particles absorb heat while in the atmosphere and darken surfaces when they eventually end up on snow or ice. But laws in California for cleaner fuels and diesel truck engines has had a positive impact on the state's air quality and warming potential.

V. Ramanathan, a professor at Scripps Institution of Oceanography, estimated the reduction in black carbon has helped to avoid about 1.4 watts of heating per square meter of the Earth's surface, Science Now reported. Greenhouse gases typically trap two to four watts of power from heat given off by the planet per square meter of heating.

Black carbon is the main component of soot and a major contributor to climate change. Some estimate black carbon may be second only to carbon dioxide in terms of driving climate change, but instead of CO2's long life in the atmosphere, black carbon only remains in the atmosphere for a few weeks, according to the Pew Center on Global Climate Change.

V. Ramanathan detailed the results in a study recently published in the journal Atmospheric Environment.

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