Sulfate pollution, which has a cooling effect, can come from coal power plants
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The clouds become darker and reflected less sun due to the drop in sulfate air pollution, and this can be responsible for a lot of recent warming beyond that caused by greenhouse gases.
“Two-thirds of global warming since 2001 are the reduction of SO2 rather than the increase in CO2,” explains Peter Cox at the University of Exeter in the United Kingdom.
Part of the sun which reaches the earth is reflected and a part is absorbed and radiated later in the form of heat. The growing carbon dioxide levels imprison this radiant heat more – a greenhouse effect that causes global warming. But the planet’s Albédo – how much it is reflected – also has a great influence on its temperature.
Since 2001, satellite instruments called Ceres directly measure the amount of sun has been reflected in relation to the amount absorbed. These measures show a fall in the quantity of sun is reflected, which means that the planet becomes darker – its albedo falls – and this causes additional warming.
There are many reasons for the falling Albédo, less snow and sea ice unless there is a cloud cover. But an analysis of Ceres data from 2001 to 2019 by Cox and Margaux walking, also to Exeter, suggests that the biggest factor is that the clouds become darker.
It is known that pollution by industry sulfate and ships can increase the density of droplets in the clouds, which makes them brighter or more thoughtful. This is the basis of a proposed form of geo-engineering, known as the clarification of marine clouds. But these programs have been successfully reduced in recent years, partly moving away from high sulfide fuels such as coal.
Walking and Cox therefore examined if the drop in the brightness of the clouds corresponded to the areas with a drop in SO2 pollution levels, and found that it was. The pair presented its preliminary results to the Climate Exeter Forum earlier this month.
The results are encouraging because the rapid warming of recent years has led some researchers to suggest that the climate sensitivity of the earth – how much it warms in response to a given increase in atmospheric CO2 – is on the high side of estimates. It turns out that additional warming due to the drop in pollution will be short -lived, while if the clouds of clouds were a feedback caused by the increase in CO2, this would mean more and more warming due to this, because CO2 levels continue to increase.
“If this darkening is a change in the properties of the clouds due to the recent decrease in SO2 emissions, rather than a change in feedback from clouds which indicates a more awaited climate sensitivity, then it is excellent news,” explains Laura Wilcox at the University of Reading in the United Kingdom, which was not involved in the study.
There are certain limits with the walking and COX data sets used, explains Wilcox. For example, data on SO2 pollution has been updated since the team analyzed.
And two recent studies have suggested that darkening is mainly due to a reduction in cloud cover, rather than darker clouds, she says. “The engines of recent darkening trends are a very debated subject at the moment.”
On the whole, however, Wilcox affirms that his own work also supports the conclusion that the recent acceleration of global warming has been mainly motivated by the decrease in air pollution, and that it is probably a temporary effect.
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