Very few people actually deny that the earth is getting warmer and that man is the cause. The real issue is the Climate Sensitivity to a doubling of CO2, and there is widespread disagreement over what that is. The IPCC gives a range of 1.5 to 4.5 degrees celsius, with them giving an average number of 3 degrees. The skeptics are on the low end of that scale, and some people are claiming it is actually higher with predictions going from 6 to 12 degrees.
It is important to note that the CO2 response is logarithmic. You have to keep doubling it to get the same effect.
The polar ice caps need a 5 degree increase to start melting. I have seen three different sources claim that it would take 5,000 years for the polar ice caps to melt, meaning that we have some time to deal with this problem. According to one source, most of our fossil fuels will run out by the year 2100, and the last one, coal, runs out by 2150. By the year 2100 we will only double the CO2 from the current level, reaching 800 parts per million. If we run out of fossil fuels then we are not going to get much higher than 800 parts per million.
There are strong reasons to think that nuclear fusion will be practical in my lifetime, which is to say in the next 20 to 30 years. We might see it in 10 years. It could make the whole argument mute.
I have repeatedly looked at the data for both CO2 and temperature from 1880 to the present. For some reason a lot of people refer to 1880 as a starting point, and I have had a hard time finding consistent data prior to that date.
In the last 138 years, the average global atmospheric temperature has gone up 1 degree celsius. That is an average increase of less than a 1/100 of a degree per year. The level of CO2 increase is around 43%. The relationship is not linear, but logarithmic, which means that if I were to multiply these figures I would get a Climate Sensitivity that is slightly too high. Still, if I do just basic math, I come up with a Climate Sensitivity of 2.33 degrees celsius, which is well within the range of what some climate skeptics have been saying all along.
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