Over at Salon (originally from Desmog Blog, I think) this chart is actually described as a “slam dunk” against “climate deniers.”
Most informed skeptics do not deny global warming — how could you, the world has clearly warmed over the last century (though some of us will argue that land-based metrics are exaggerating that warming). We skeptics don’t even deny that CO2 causes some warming. In my case I accept Michael Mann’s old number of about 1C of warming (before feedbacks) from a doubling in CO2.
What we skeptics “deny” is the catastrophe — that hypothesized positive feedbacks in the Earth’s climate system will multiply the initial warming from CO2 many times, raising it from a manageable one degree or less over the next century to three or five or ten degrees. Skeptics believe that temperatures will rise due to CO2, but will remain within the bounds of temperatures we have already seen over the last millenia, including those in the Medieval Warm Period during which European civilization thrived.
And we believe that the cost of economic dislocations, particularly in developing countries, from limiting fossil fuel consumption will be far worse than from merely adapting to a one degree change.
What fair-minded person could possibly imagine this black circle in any way is a rebuttal to this skeptic position?