I'm not under-quoting anything. The average temperature of the Earth is about 15 degrees C, which is 288 Kelvin. A change of 1 degree is 1/288 = 0.35%.
That's actually one of the big points that gets lost in this debate. Deniers love to say that the "tiny" quantity of CO2 in the atmosphere can't possibly have such a big effect. It's not having a big effect, on an absolute scale. The problem for us is that a small change in absolute temperature is still a big shift relative to the range of temperatures we (and current living creatures) are adapted to.
