Most Warming This Century May Be Due To Air Pollution Cuts

Arthur T Knackerbracket has processed the following story:

Satellite data suggests cloud darkening is responsible for much of the warming since 2001, and the good news is that it is a temporary effect due to a drop in sulphate pollution

Clouds have been getting darker and reflecting less sunlight as a result of falling sulphate air pollution, and this may be responsible for a lot of recent warming beyond that caused by greenhouse gases.

Two-thirds of the global warming since 2001 is SO2 reduction rather than CO2 increases," says Peter Cox at the University of Exeter in the UK.

Some of the sunshine that reaches Earth is reflected and some is absorbed and later radiated as heat. Rising carbon dioxide levels trap more of that radiant heat - a greenhouse effect that causes global warming. But the planet's albedo - how reflective it is - also has a big influence on its temperature.

Since 2001, satellite instruments called CERES have been directly measuring how much sunlight is reflected versus how much is absorbed. These measurements show a fall in how much sunlight is being reflected, meaning the planet is getting darker - its albedo is falling - and this results in additional warming.

There are many reasons for the falling albedo, from less snow and sea ice to less cloud cover. But an analysis of CERES data from 2001 to 2019 by Cox and Margaux Marchant, also at Exeter, suggests the biggest factor is that clouds are becoming darker.

It is known that sulphate pollution from industry and ships can increase the density of droplets in clouds, making them brighter or more reflective. This is the basis of one proposed form of geoengineering, known as marine cloud brightening. But these emissions have been successfully reduced in recent years, partly by moving away from high-sulphur fuels such as coal.

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