Hoffmann cites two recent papers that investigate Forbush decreases and their impacts on clouds, and thus climate. The two papers reach different conclusions.
The first paper is by Calogovic et al. (Jürg Beers Gruppe) in GRL, which analyses the 26 strongest Forbush events beginning in 1989 and compares them to ISCCP cloud data. This Calogovic paper finds nothing. No systematic changes in low cloud cover were associated with Forbush events.
The second paper by a German team, Rohs et al, appeared in the Journal of Geophysical Research and found a faint but detectable correlation that seems to contradict Svensmark’s hypothesis that low, earth-cooling clouds would be produced. Rather, Rohs et al finds that high, earth-warming type cirrus clouds are produced instead.
That would be astonishing because it would mean that periods of low solar activity would cause warm periods, and not cold ones, thus completely flying in the face of the Maunder and Dalton minimums.
The Rohs team used Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) data, which uses so-called limb-viewing of the atmosphere. Six Forbush events over 1.5 years were analysed.
Although Hoffmann admits that 6 Forbush events in 1.5 years is a scant amount of data, he can hardly contain his glee with Rohs’s findings and deems them sufficient enough to openly taunt proponents of Svenmark’s hypothesis. He even singles out the “usual suspects”: THE HOCKEY SCHTICK and GREENIE WATCH, here and here respectively, for claiming Rohs’s paper supported Svensmark. THE HOCKEY SCHTICK and GREENIE WATCH did not mention that the clouds formed in the Rohs paper were of the high, warming kind.
Of course, in a reader comment, I asked why the long periods of long protracted solar inactivity during the Manunder Minimum and Dalton Minimum did not lead to warming. Why was it cold instead? Hoffmann replies with interesting speculation:
Concerning the Maunder Minimum. So IF the Rohs relationship turns out to be robust, it is in fact the wrong sign fo the suggested sun/climate relation. Then you have a couple of other possibilities: 1) Direct forcing (TSI) is sufficient to compensate the Cirrus effect. That means a comparably high climate sensitivity. 2) Volcanoes were mainly responsible for the Maunder Minimum and compensated the Cirrus effect 3) The target is not clear meaning there is no clear relationship between the sun and climate.
For the moment I tkink one has to wait for more MIPAS data. Svensmark idea is by any means not even close to something verfied.
I wonder if he realises what he is saying. If Rohs turned out to be robust ( I doubt it will), then it would turn climate science on its head. Now that would be most interesting.
Note: Georg Hoffmann is a researcher at the LSCE (Laboratory of Sciences of Climate and Environment) in Paris and focuses on various aspects of paleo-climatology. His area of specialty includes climate reconstruction of the last 1000 years and the coupling of carbon cycles to climate development on paleo-timescales.
UPDATE: HOCKEY SCHTICK REPLIES:
1. The abstract says they only looked at mid and high altitude clouds, so nothing can be concluded from this study about low altitude clouds & GCRs
2. The abstract says “a 15% increase in CNM would result in … an increase in cloud opacity,” so unless the abstract is worded incorrectly, there is no problem with the sign of the correlation. This would also be consistent with earlier statement of a “positive cloud-CNM correlation.”
3. The claim that high altitude clouds warm the planet because they “absorb more IR and reflect less sunlight” seems tenuous at best. Incoming solar energy is 45% IR, so these clouds absorb significant amounts of solar energy BEFORE it reaches the earth, thus acting as a sunshade. Furthermore, high altitude clouds at -18C or less are not capable of heating the earth at 15C because “a cold body cannot heat a warm body” from the 2nd law of thermodynamics.