The paper – Rethinking the lower bound on aerosol radiative forcing by Bjorn Stevens of the Max Planck Institute for Meteorology in Hamburg, Germany, published in the American Meteorological Society journal – finds that the effects of aerosols on climate are much smaller than those in almost all the computer models used by the Intergovernmental Panel on Climate Change.
Aerosols are the minute particles added to the atmosphere by burning fossil fuels (as well as by non-anthropogenic sources, like volcanoes). The reason they are important is that they are so often cited by alarmists to excuse the awkward fact that the world has stubbornly failed to warm at the disastrous rate they predicted it would.
Apparently – or so the excuse goes – these aerosols are masking the true extent of runaway climate change by cancelling out the effects of man-made CO2.
Here, for example, is a NASA expert in 2009:
Using climate models, we estimate that aerosols have masked about 50 percent of the warming that would otherwise have been caused by greenhouse gases trapping heat near the surface of the Earth
Here is a report on a study from another institution – NOAA – with a long track record of ramping up the alarmist cause.
A new study led by the U.S, National Oceanic and Atmospheric Administration (NOAA) shows that tiny particles that make their way all the way up into the stratosphere may be offsetting a global rise in temperatures due to carbon emissions.
Aerosols are often used to explain the lack of “global warming” in the cooling period between 1940 and 1970 (when the growth in industrialisation and all that extra man-made CO2 ought to have begun taking effect).
They have also been used in this 2011 paper – whose co-authors include one Michael Mann, which gives you an idea of its quality and reliability – for the Proceedings of the National Academy of Sciences of the USA (PNAS). It claims that the reason there has been a “hiatus” in global warming since 1998 is because of the effect of aerosol emissions. This got one of the BBC’s resident alarmists Richard Black very excited. He wrote it up in an article entitled Global warming lull down to China’s coal growth. (Oddly he forgot to surround it with scare quotes, or finish it with a question mark.)
The new Stevens paper has been described as a “game-changer” by one expert in the field, Nic Lewis.
According to the IPCC’s models, the effect of aerosols on climate could be as much as 4.5 degrees C. But Stevens paper suggests that this is a considerable overestimate and that the reduction they effect on temperature cannot be more than 1.8 degrees C.