Read here. Almost all scientists agree that an increase in atmospheric CO2 will only raise global temperatures from 1.0 to 1.5 degrees Celsius. The IPCC is well aware of this established science, so they had scientists add a hypothetical positive feedback to the climate models, which would then produce predictions of much higher temperatures.
Terrestrial nature abhors positive feedbacks; that's why the climate is dominated by negative feedbacks. IPCC scientists hate natural negative feedbacks because they automatically reduce future global warming, and that's why the IPCC climate models either minimize negative feedbacks or entirely ignore them. Unfortunately for the IPCC Climategate scientists, the science research continues about natural climate feedbacks, which has now led to a new major negative feedback being identified in a new region of the world by peer-reviewed research.
Simply put, Geibert et al. found as warming increases, more sea ice and icebergs are melting in the Southern Ocean. This freshwater melt decreases the salinity of water, while increasing the iron content in layers of the sea, allowing for a huge increase in phytoplankton blooms. The new phytoplankton blooms cause more CO2 absorption (i.e. sequester CO2) from the atmosphere, which is then transported to the ocean depths.
Depending on the specific climate model, this natural negative feedback of CO2 sequestration is completley ignored or accounted for in minimal terms.
"The authors write that "the Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes,"...the eleven researchers -- hailing from Germany, New Zealand, South Africa and the United Kingdom.....state that their findings "imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO." And if those changes were to include enhanced melting of Antarctic sea ice and icebergs, such as climate alarmists continually claim will occur, the planet's deep-ocean carbon transferal system would shift into a higher gear and effectively sequester greater amounts of CO2-carbon from the atmosphere, reducing its rate of rise and thereby reducing the strength of the CO2 greenhouse effect." [W. Geibert, P.Assmy, D.C.E. Bakker, C. Hanfland, M. Hoppema, L. Pichevin, M. Schröder, J. N.
Schwarz, I. Stimac, R. Usbeck, A. Webb 2010]