VEERABHADRAN Ramanathan, one of the world's leading climate scientists, weaved through a warren of mud brick huts, each containing a mud cooking stove pouring soot into the atmosphere.
Pausing to make his point, he said: "It's hard to believe that this is what's melting the glaciers."
As women in ragged saris of a thousand hues bake bread and stew lentils in the early evening over fires fuelled by twigs and dung, children cough
from the dense smoke that fills their homes. Black grime coats the undersides of thatched roofs. At dawn, a brown cloud stretches over the landscape like a dirty blanket.
In Kohlua, in central India, with no cars and little electricity, emissions of carbon dioxide, the main heat-trapping gas linked to global warming, are near zero. But soot – also known as black carbon – from tens of thousands of villages like this one, is emerging as a major and previously unappreciated source of global climate change.
While carbon dioxide may be the No 1 contributor to rising global temperatures, scientists say, black carbon has emerged as an important No 2, with recent studies estimating that it is responsible for 18% of the planet's warming, compared with 40% for carbon dioxide.
Decreasing black carbon emissions would be a relatively cheap way to significantly rein in global warming.
Replacing primitive cooking stoves with modern versions that emit far less soot could provide a much-needed stop-gap, while nations struggle with the more difficult task of enacting programmes and developing technologies to curb carbon dioxide emissions from fossil fuels.
"It is clear to any person who cares about climate change that this will have a huge impact on the global environment," said Ramanathan, a professor of climate science at the US Scripps Institute of Oceanography, who is working on a project to help poor Indian families acquire new stoves.
"In terms of climate change, we're driving fast toward a cliff, and this could buy us time," Ramanathan said.
Better still, decreasing soot could have a rapid effect. Unlike carbon dioxide, which lingers in the atmosphere for years, soot stays there for a few weeks. Converting to low-soot stoves would remove the warming effects of black carbon quickly, while shutting a coal plant takes years to substantially reduce global CO2 concentrations.
But the awareness of black carbon's role in climate change has come so recently that it was not even mentioned as a warming agent in the 2007 summary report by the Intergovernmental Panel on Climate Change that said the evidence for global warming was "unequivocal".
In Asia and Africa, stoves produce the bulk of black carbon, although it also emanates from diesel engines and coal plants. In the US and Europe, black carbon emissions have already been reduced significantly by filters and scrubbers.
Like tiny heat-absorbing black sweaters, soot particles warm the air and melt the ice by absorbing the sun's heat when they settle on glaciers. One recent study estimated that black carbon might account for as much as half of Arctic warming.
Soot from India has been found in the Maldive islands and on the Tibetan Plateau; from the US, it travels to the Arctic. The environmental and geopolitical implications of soot emissions are enormous. Himalayan glaciers are expected to lose 75% of their ice by 2020.
These glaciers are the source of most of the major rivers in Asia. The short-term result of glacial melt is severe flooding in mountain communities.
Once the glaciers shrink, Asia's big rivers will run low or dry for part of the year, and desperate battles over water are certain to ensue in a region already rife with conflict.
The fact that remote rural villages such as Kohlua could play an integral role in tackling the warming crisis is hard to imagine. There are no cars, no running water and only intermittent electricity, which powers a few light bulbs.
The 1,500 residents here grow wheat, mustard and potatoes and work as day labourers in Agra, home of the Taj Majal, about two hours away by bus.
They earn about £1.30 a day and, for the most part, have not heard about climate change, despite recent droughts blamed by scientists on global warming.
Doctors have long railed against black carbon for its devastating health effects in poor countries. The combination of health and environmental benefits means that reducing soot provides a "very big bang for your buck", said Erika Rosenthal, a senior lawyer at Earth Justice, a Washington organisation.
"Now it's in everybody's self interest to deal with things like cooking stoves – not just because hundreds of thousands of women and children far away are dying prematurely."
