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What's this? CO2 causes warming which raises sea temperature which increases evaporation causing clouds that cool. Sounds like a negative feedback effect. Any estimate of the magnitude of this negative feedback? Has it been factored into the models?

To an extent. Cloud processes are still one of the largest uncertainties in the models. Observations such as this one help improve the models.

Cloud processes are still one of the largest uncertainties in the models. Observations such as this one help improve the models.

So do observations such as these:

Variation in low level cloud cover have also been shown to be substantially related to solar activity.

FIG. I. Composite figure showing changes in Earth's cloud cover from four satellite cloud data sets together with cosmic ray fluxes from Climax (solid curve, normalized to May 1965) and 10.7 cm solar Bur (dashed curve, in units of 10-22 Wm-2 Hz-2). Triangles are the Nimbus7 data, squares are the ISCCP C2 and ISCCP_D2 data, diamonds are the DMSP data. All of the displayed data have been smoothed using a 12 month running mean. The Nimbus7 is for the southern hemisphere over oceans with the tropics excluded. The DMSP data are total cloud cover for the southern hemisphere over oceans, and finally the ISCCP data have been derived from geostationary satellites over oceans with the tropics excluded. Also shown are 2-standard-deviation error bars for the three data sets, one for each 6 months.

and is the subject of a current research project at CERN.

Contents of CERN 2001-007
Workshop on ion-aerosol-cloud interactions

http://preprints.cern.ch/cernrep/2001/2001-007/2001-007.html
http://cloud.web.cern.ch/cloud/iaci_workshop/proceedings.html

Contents of CERN 2001-007Workshop on ion-aerosol-cloud interactions

Contents of CERN 2001-007
Workshop on ion-aerosol-cloud interactions