Short-term pollution has far reaching effect
Toxic gases and particles which stay in the atmosphere for just a few weeks have been shown to have a greater influence on the global climate than previously thought.These pollutants can also affect the weather half way around the world, even though they tend to originate from pockets of densely populated or industrialised land.
These are the conclusions of research undertaken by the USA's National Oceanic & Atmospheric Administration (NOAA) into the influence of soot, low altitude ozone and airborne nitrates and sulphates.
The study claims that this kind of pollution in Asia will lead to hotter, drier summers in the USA by the middle of the century.
Each type of pollution influences surface temperatures differently --sulphate particles reflect sunlight so have a cooling effect, for example, while black carbon particles - or soot - acts as microscopic storage heaters by absorbing warmth then releasing it again later.
"Previous research suggests that the warming of the surface climate by increasing levels of long-lived greenhouse gases has been partially offset by increasing levels of those short-lived particles that reflect sunlight," said Hiram Levy, senior research scientist at NOAA.
"This study found that over the 21st century the climate impacts of projected changes in human emissions of short-lived gases may in fact enhance global warming."
While short-lived pollutants are generated locally and tend to be concentrated close to their source, they exert a global influence.
The report cites a climate model projection of emissions and pollutant levels over Asia that results in a rise in temperature and a decline in rainfall over the continental United States during the summer throughout the second half of this century.
"By 2050, projected changes in short-lived pollutant concentrations in two of the three studies are responsible for approximately 20 percent of the simulated global-mean annual average warming," said Drew Shindell, NASA climate scientist and co-author of the report.
"However, these climate impacts depend on emission forecasts far into the future, and the range of reasonable emissions projections is very large, even for a single economic and technology storyline [such as the use of coal in Asia]."
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