The Economist has rather perspicaciously realised that aerosols have emerged from the Fifth Assessment Report as one of the most interesting talking points, and covers the area in some depth in this week's issue.
The IPCC report itself suggests that
There is high confidence that aerosols and their interactions with clouds have offset a substantial portion of global mean forcing from well-mixed greenhouse gases.
However, the tweets coming out of the Royal Society meeting last week suggested that scientists were in fact completely divided on this question:
Gavin Schmidt: How much aerosol is anthropogenic is still not sufficiently quantified!
Olivier Boucher: Boucher: no correlation of aerosol forcing and CS in CMIP5 ensemble
Olivier Boucher: Absorption optical depth for low amounts of aerosol is highly uncertain and the last great unknown in aerosol radiative effect
Olivier Boucher: We don't yet have a good handle on the amount on absorbing aerosol in the Earth's atmosphere
It's interesting to see scientists expressing high levels of uncertainty among themselves (albeit in a semi-public arena) but broadcasting great certainty to the public. It's a pity then that the Economist piece is helping this process along, with no sense of scientists continued difficulties with the subject.
Nor, alas, does the article make the connection between low aerosol forcing and low climate sensitivity; one comes away from reading it with the impression that we should expect more warming because the cooling effect of aerosols is less. As readers here know, in order to hindcast the past correctly, models either have to have low ECS and low aerosol forcing or high ECS and high aerosol forcing. Other things being equal, the evidence of low aerosol forcing is good news for the future.