Some call it black carbon, others BC, while most know it as soot. But whatever the name, the tiny black particles streaming from tailpipes and chimneys are proving to be a bigger climate headache than previously thought. Scientists are just beginning to appreciate how soot, the 'forgotten carbon', is affecting the climate - and on the need for action.
Now a Stanford University chemist, Mark Jacobson - who is speaking at this week's ACS (American Chemical Society) meet in Denver - is pushing for soot-controls to be the top priority for getting the climate back under control. He believes that a 'soot first' strategy could be the fastest, and cheapest, way of slowing global warming. It could even help halt the precipitous decline in the Arctic's ice sheets, and help stop millions of preventable deaths.
The need for fast action on soot comes from a new understanding of how the minute black particles punch above their size, both in the atmosphere and on the ice caps. That's all because of their color. Soot particles are black, and so readily absorb light from the sun, and the energy reflected from the earth's surface - and so heat up, just like black leather car-seats on a hot sunny day.
Melting the clouds
In the clouds, the presence of black carbon particles, both in water droplets and between them, has a surprising effect. The extra heat absorbed by the soot can cause the water droplets to evaporate more quickly, so making the clouds melt away. Depending on the height of the cloud, that can have an overall warming affect, as much sunlight is usually reflected off of the tops of clouds.
Soot also plays a heat-gathering role over the frozen wastes of ice sheets and glaciers. Whilst snow and ice reflect sunlight, black carbon absorbs it - so soot settled onto the cold surface helps to speed up melting. Jacobson has included all of these effects into a more sophisticated global climate model, to try and get a better grasp of soot's warming potential. The results show that soot may in fact surpass the role played by methane, making it the second-most important warming pollutant after CO2.
That is in fact good news in the battle to prevent climate change. Soot is a very different pollutant to carbon dioxide or methane - it falls from the air after a few days. CO2 is infinitely more tardy - staying in the atmosphere for hundreds of years. So while cutting CO2 now will not halt the warming already 'built-in', cutting soot could have a dramatic and sudden impact.
"No other measure could have such an immediate effect," said Jacobson. "Soot emissions account for about 17 percent of global warming, more than greenhouse gases like methane. Soot's contribution, however, could be reduced by 90 percent in 5-10 years with aggressive national and international policies." His model suggests that such action could make a huge difference in one of the climate hot-spots of the globe - the Arctic. If he's right, up to 3 degrees Fahrenheit could be slashed off of temperatures there, in less than two decades - effectively resetting the north pole to where it was before the 20th century began.
Reset for Arctic warming?
Given that the rapid melting of the Arctic ice-sheet is one of the most visible, and worrying signs of global warming, having a possible reset button to hand could be a huge step forwards. But to grasp the prize, the world will need to tackle the soot issue as one - and quickly. Fortunately, controlling soot is much less of a challenge than controlling CO2.
The technology is already there - filters for diesel engines, or low-soot cookers for burning wood and dung in the developing world - and relatively low cost. And the benefits of soot control don't just stop at reining in climate change. Particulate pollution is a major cause of ill-health and premature death across the world. Cut the soot, and those deaths could be reduced significantly.
So if the will is there, putting a sock on the soot could turn out to be a spectacular win-win environmental control measure.
Top Image Credit: © barunkevin