They also discuss some indications of higher
aerosol cooling in the last decade, considered as a potential influence (although not dominant) in 21st century temperatures.
The only info I can find, including your posting above, talks about the general increase from about 1910 to 1945, followed
by aerosol cooling until around 1975.
Another candidate is climate forcings other than CO2 such
as aerosol cooling being smaller than expected.
It's a subtle argument,
because aerosol cooling has clearly been less than greenhouse warming — if not, the planet wouldn't have gotten warmer over the last century.
But
if aerosol cooling is larger than generally assumed, the planet will warm more rapidly than predicted as soon as aerosol levels fall.
Actually, although my most recent comment
sets aerosol cooling to zero, we should be careful about minimizing aerosol leverage in this time period.
If there's much less mid-century cooling, that will conflict with an assumed
strong aerosol cooling effect in the models, and by implication, a strong CO2 warming effect.
Thus the human
made aerosol cooling (and changes in cooling with changes of emissions) should be seen in the main wind direction of the sources, which are by far largest in the NH.
runup from 1910 - 1940 than lack of volcanic activity and a better explanation for the 1940 - 1979 hiatus than
industrial aerosol cooling.»
A key factor in identifying the aerosol fingerprint, and therefore the amount of
aerosol cooling counteracting greenhouse warming, is the change through time of the hemispheric temperature contrast, which is affected by the different evolution of aerosol forcing in the two hemispheres as well as the greater thermal inertia of the larger ocean area in the SH (Santer et al., 1996b, c; Hegerl et al., 2001; Stott et al., 2006c).
The authors conclude from an inverse structural analysis that the CanESM2, GFDL - CM3and HadGEM - ES models all strongly overestimate GHG warming and compensate by a very strongly
overestimated aerosol cooling, which simulates AMO - like behaviour with the correct timing — something that would not occur if the models were generating true AMO behaviour from natural internal variability.
There could also be errors in our estimates of the magnitudes of other climate forcing terms —
especially aerosol cooling — or, as mentioned earlier, time lags in how the climate system responds.
perseus @ 2 - the pre-1975 ocean data in this paper look similar to the surface data, in that they did not warm much during mid-century, likely due to
aerosol cooling offsetting greenhouse gas warming.
The GCMs appear to be wrong not only because they assume too
much aerosol cooling, but also because, a) most of them arrive at a too - high temperature change between the 1880 - 1890 and 2000 - 2010 time frames, and b) because they generally predict too much ocean heat uptake, particularly in the Southern Hemisphere.
Furthermore, if aerosols did have such a dramatic cancelling effect at the onset of WWII and during the following decades, is
aerosol cooling part of the temperature models?
This study found that black carbon has a warming effect of approximately 0.9 W / m2,
while aerosol cooling effects account for approximately -2.3 W / m2.