Soot revealed as major cause of global warming

Soot pouring out of trucks and chimneys is having a major worsening effect on global warming, scientists said today.

The impact of soot in the atmosphere on climate is much larger than was previously realised, a new study has shown.

It could even be responsible for a quarter of observed global warming, say the researchers.

Soot, mainly composed of black carbon, is the dusty by-product of burning fossil fuels and vegetation.

Levels are highest over China and India, where coal and biofuels are burned in households. Europe and North America were the major source is diesel fuel.

Soot warms the Earth by darkening snow and ice, causing it to absorb rather than reflect sunlight.

Two Nasa scientists have now found that soot is twice as effective as carbon dioxide at raising global surface air temperature.

James Hansen and Larissa Nazarenko, from the American space agency’s Goddard Institute for Space Studies in New York, said high soot emissions might be substantially contributing to earlier spring melts.

It could also be helping glaciers, sea ice and ice sheets to melt at lower temperatures, because black carbon absorbs more energy than clean snow and ice.

The researchers wrote in the journal Proceedings of the National Academy of Sciences: “This indirect soot forcing may have contributed to global warming of the past century, including the trend toward early springs in the northern hemispheres, thinning arctic sea ice, and melting land ice and permafrost.”

They suggested reducing soot emissions – a move that has not yet been considered by the international community.