For many years, people have thought of aerosol cans as being bad for the environment but it seems aerosols - tiny, airborne particles - have slowed the rise in global temperatures over the past decade.
American researchers have measured the effect aerosols in the upper atmosphere have had on climate change, building on past research that has identified the temporary cooling effect of these molecules in other parts of the atmosphere.
The researchers believe the increase in aerosols comes from coal-fired power stations in developing countries, many of whom do not require their power stations to contain their sulphate emissions.
But the slowed increase in temperatures in the past decade is minor compared with the rapid, sustained increase in global temperatures over the past century.
When released into the atmosphere, sulphate aerosols reflect incoming sunlight, cooling the climate system as a result - a phenomenon known as global dimming.
The two main sources of the molecules are man-made activities, such as burning fossil fuels, and natural events such as volcanic eruptions.
American researchers used satellite data to measure the change in sulphate aerosol concentration in the stratosphere, which extends above 15 kilometres, over the past 60 years.
The team, whose findings are published in the journal Science, then used these measurements to estimate the contribution the molecules made to global temperature and sea level rise.
They found an increase in aerosols in the upper atmosphere has decreased the global warming that would have otherwise occurred by 20 per cent over the past decade.
Because the last major volcanic eruption occurred two decades ago, when Mount Pinatubo erupted in the Philippines, the researchers suggest the increase in aerosol concentration in the upper atmosphere in the past decade has been from developing countries burning fossil fuels.
Most developed countries have stringent regulations that stop coal-fired power stations from releasing particulate matter, which has serious health effects.
But an Australian climate scientist, David Karoly, said the small slowdown in global temperature rises over the past decade was outweighed significantly by the overall warming of the planet over the past 100 years.
”You can’t offset lots of global warming by these natural or possibly human-related increases in aerosols in the upper atmosphere,” said Professor Karoly from the University of Melbourne.
Aerosols in the upper atmosphere were not the only factor to slow the rise in global temperature over the past 13 years, he said. Natural climate variability and increases in aerosols in the lower atmosphere also played a role, he said.
But Professor Karoly said the new findings would add to the collective knowledge on climate change and should be used to further refine future climate projections.
