Richard Lindzen and Yong-Sang Choi write:
CO2, a relatively minor greenhouse gas, has increased significantly since the beginning of the industrial age from about 280 ppmv to about 390 ppmv, presumably due mostly to man’s emissions. This is the focus of current concerns. However, warming from a doubling of CO2 would only be about 1 degree C (based on simple calculations where the radiation altitude and the Planck temperature depend on wavelength in accordance with the attenuation coefficients of well-mixed CO2 molecules; a doubling of any concentration in ppmv produces the same warming because of the logarithmic dependence of CO2’s absorption on the amount of CO2) (IPCC, 2007).
This modest warming is much less than current climate models suggest for a doubling of CO2. Models predict warming of from 1.5 degrees C to 5 degrees C and even more for a doubling of CO2. Model predictions depend on the ‘feedback’ within models from the more important greenhouse substances, water vapor and clouds. Within all current climate models, water vapor increases with increasing temperature so as to further inhibit infrared cooling.
Clouds also change so that their visible reflectivity decreases, causing increased solar absorption and warming of the earth. Cloud feedbacks are still considered to be highly uncertain (IPCC, 2007), but the fact that these feedbacks are strongly positive in most models is considered to be an indication that the result is basically correct. Methodologically, this is unsatisfactory…
Our study also suggests that, in current coupled atmosphere-ocean models, the atmosphere and ocean are too weakly coupled since thermal coupling is inversely proportional to sensitivity (Lindzen and Giannitsis, 1998). It has been noted by Newman et al. (2009) that coupling is crucial to the simulation of phenomena like El Niño. Thus, corrections of the sensitivity of current climate models might well improve the behavior of coupled models, and should be encouraged. It should be noted that there have been independent tests that also suggest sensitivities less than predicted by current models. These tests are based on the response to sequences of volcanic eruptions (Lindzen and Giannitsis, 1998), on the vertical structure of observed versus modeled temperature increase (Douglass, 2007; Lindzen, 2007), on ocean heating (Schwartz, 2007; Schwartz, 2008), and on satellite observations (Spencer and Braswell, 2010).
Most claims of greater sensitivity are based on the models that we have just shown can be highly misleading on this matter. There have also been attempts to infer sensitivity from paleoclimate data (Hansen et al., 1993), but these are not really tests since the forcing is essentially unknown given major uncertainties in clouds, dust loading and other factors. Finally, we have shown that the attempts to obtain feedbacks from simple regressions of satellite measured outgoing radiation on SST are inappropriate.
One final point needs to be made. Low sensitivity of global mean temperature anomaly to global scale forcing does not imply that major climate change cannot occur. The earth has, of course, experienced major cool periods such as those associated with ice ages and warm periods such as the Eocene (Crowley and North, 1991). As noted, however, in Lindzen (1993), these episodes were primarily associated with changes in the equator-to-pole temperature difference and spatially heterogeneous forcing. Changes in global mean temperature were simply the residue of such changes and not the cause.
Meanwhile from the UK:
CERN’s 8,000 scientists…have made an important contribution to climate physics, prompting climate models to be revised. The first results from the lab’s CLOUD (“Cosmics Leaving OUtdoor Droplets”) experiment published in Nature today confirm that cosmic rays spur the formation of clouds through ion-induced nucleation. Current thinking posits that half of the Earth’s clouds are formed through nucleation. The paper is entitled Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. This has significant implications for climate science because water vapour and clouds play a large role in determining global temperatures. Tiny changes in overall cloud cover can result in relatively large temperature changes…
Climate models will have to be revised, confirms CERN in supporting literature: “it is clear that the treatment of aerosol formation in climate models will need to be substantially revised, since all models assume that nucleation is caused by these vapours and water alone.” The work involves over 60 scientists in 17 countries.