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Summary High estimates of climate sensitivity to greenhouse gases assume aerosols caused a large cooling effect, which canceled some of the previous warming effect, and little or no natural climate change.Recent research indicates that the aerosol effect is much less than previously thought.
They were chosen to give the longest early and late periods free of significant volcanic activity, which provide the largest change in forcing and hence the narrowest uncertainty ranges.
Using the FUND integrated assessment model results, the mean estimate of the social cost of carbon on a global basis is determined to be -17.7 US$/tonne of CO.
The benefits of carbon dioxide fertilization, longer growing season, greater arable land area, reduced mortality and reduced heating costs greatly exceed harmful effects of warming.
Using the equations for TCR and ECS, the total forcing change during the interval was 2.21 W/m.
Adjustment for Millennium Cyclic Warming This analysis by Lewis does not account for the long-term natural warming from the Little Ice Age (LIA), likely driven by indirect solar activity.
The temperature history shows an obvious millennium scale temperature oscillation, indicating that natural climate change accounts for a significant portion of the temperature recovery since the LIA. Richard Lindzen writes, “Lewis does not take account of natural variability, and, I suspect, his estimates are high.” Fredrik Ljungqvist prepared a temperature reconstruction of the Extra-Tropical Northern Hemisphere (ETNH) during the last two millennia with decadal resolution [Ljungqvist 2010] here emissions to 1900 were insignificant.