The science is not settled! -----------------------------
"FAR from warming the planet rapidly, man-made pollution might actually be contributing to a slowing of global warming, a US study suggests. Aerosol particles from activities such as burning coal, particularly in the past decade, reflect sunlight back into space, slowing the rapid warming observed up to and including 1998.
Reporting in the journal Science today, study leader Susan Solomon, of the National Oceanographic and Atmospheric Administration, says she and her team observed that an increase in stratospheric aerosols had cut by 20 per cent the global warming that would have otherwise occurred since 1998.
The paper also suggests that increased concentrations of aerosols cut by 0.05C the global warming that would otherwise have occurred between 1960 and 2000.
Since 1960 the mean temperature in Australia has risen by about 0.7C.
Start of sidebar. Skip to end of sidebar. .End of sidebar. Return to start of sidebar. According to World Meteorological Organisation data, last year, 2005 and 1998 were the globe's warmest years on record.
Atmospheric aerosols are tiny solid or liquid particles that can come from volcanoes, sea salt or dust, but also from anthropogenic activity, such as the burning of fossil fuels, which send sulphur dioxide into the atmosphere.
Natural aerosols from volcanoes, notably massive eruptions at El Chichon in Mexico in 1982 and Pinatubo in The Philippines in 1991, have slowed global warming at times.
But the Solomon study suggests that in the absence of huge eruptions since Pinatubo (Iceland and Chile eruptions are too recent) a rise in man-made aerosols has reflected enough sunlight to alone slow the pace of global warming.
The paper says: "Some studies have suggested that an important source of the background stratospheric aerosol layer may be anthropogenic sulphur (SO2 from coal burning and biomass burning)."
Combining ground-based and satellite measurements, the scientists observed "increases in stratospheric aerosols from 2000 to 2010 of about 7 per cent per year. Over the decade since 2000, carbon dioxide increased by about 0.5 per cent per year".
University of Melbourne meteorologist David Karoly said the study provided "the most complete evaluation of background levels (of aerosols) and how they have increased over the last decade or so".
"What this paper does is estimate the contribution of this increased amount of aerosols in the stratosphere (15km to 50km above earth) to cooling the climate system over last decade," Professor Karoly said.
"It says this might have masked as much as a quarter of the contribution from increased greenhouse gases in fossil fuel burning in developing countries such as China and India.
"Another possibility not mentioned in paper is . . . large bushfires injecting particles into the stratosphere in what are called pyrocumulus clouds that act as a way of transporting aerosols from the lower atmosphere to the stratosphere. There have been a number of studies showing that might be an important source.""
