William Lau and colleagues at NASA’s Goddard Space Flight Center simulated the movement of air masses in the region from 2000 to 2007 and then factored in analyses of how soot particles and aerosols absorb the sun’s heat. They found that the soot – also known as black carbon – which is produced by diesel engines, coal-fired power plants and outdoor cooking stoves in South Asia, is carried east on wind currents and then accumulates on the Tibetan Plateau. There, it either remains airborne, or is deposited on the ground surface.

The particles’ dark colour absorbs solar radiation, creating a layer of warm air just above the surface and also directly melting the ice and snow. The scientists estimate that the amount of warming could contribute as much or more to warming in the region as greenhouse gases.

‘Over areas of the Himalaya, the rate of warming is more than five times faster than warming globally,’ said Lau. ‘Based on the differences, it isn’t difficult to conclude that greenhouse gases are not the sole agents of change in this region. There’s a localised phenomenon at play.’

The results are backed up by new research by scientists from NASA and the Chinese Academy of Science. Analysis of ice cores from five sites on the Tibetan Plateau suggests that soot deposition has increased by around 30 per cent since 1990.

February 2010