Study - Climate Scientists "Erring On The Side Of Least Drama" W. Overly Conservative Projections
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Arctic Sea Ice Decline
Three years after the IPCC Fourth Assessment Report was drafted, the 2009 Copenhagen Diagnosis examined the latest climate research to effectively update the IPCC report. In addition to confirming the Rahmstorf finding that the IPCC has underestimated sea level rise, the Copenhagen Diagnosis also found that the IPCC has dramatically understimated the decline in Arctic sea ice extent (Figure 2).
Figure 2: Observed vs. IPCC modeled annual minimum Arctic sea ice extent
In 2012, Arctic sea ice melt shattered the previous record low, to levels unseen in millennia, increasing the margin by which IPCC projections have been too conservative.
CO2 Emissions
A 2009 report by the US National Research Council (NRC), Committee on Strategic Advice on the U.S. Climate Change Science Program found that the IPCC had also underestimated recent CO2 emissions from developing countries.
"The IPCC projections are based on estimates that CO2 emissions in China increased at an annual rate of about 3 to 4 percent during the past 10 years (IPCC, 2007a; IEA, 2007), but a subsequent province-based inventory concluded that emissions actually increased at a higher rate of about 10 to 11 percent (Auffhammer and Carson, 2008)....Emissions from a number of other developed countries were also higher than agreed-to targets."
The Copenhagen Diagnosis similarly found that in addition to underestimating sea level rise, human CO2 emissions have tracked towards the highest IPCC scenarios.
Figure 3: IEA fossil fuel CO2 emissions estimates vs. IPCC SRES emissions scenarios.
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http://www.skepticalscience.com/climate-scientists-esld.html
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My denier friends refuse to look at it. 
--imm
