The curves shown in the diagram are from Knutti and Hegerl 2008 a paper that alleges to show corroborating evidence for high sensitivity (how much warming there will be with a doubling of CO2). Their claim of about 3C is important because if sensitivity is not high then the manmade increase in CO2 will only cause benign warming, not "catastrophic" warming.
The part of the diagram (pictured on the right) that Skeptical Science (on the left) likes to leave off is the colored blocks. The blocks show that the estimates of climate sensitivity derived from ice age climate data are not applicable to today's climate (and cannot be used as evidence to corroborate high sensitivity).
Frankly, SkepticalScience.com is not interested in presenting all the facts, but rather a narrative of catastrophic global warming that leaves off these caveats about the high sensitivity required for catastrophic global warming. The bottom line from the chart with blocks is that the only prediction for catastrophic global warming comes only from climate models that are tuned to have high sensitivity, a circular argument.