I've explained this before. CO2 is a greenhouse gas. If its concentration goes up, temperature must too. Its a physical property of CO2.
Why does this remind me of Franko? This tedious repetition of a syllogism over and over as if the repetition makes the case stronger.
CO2 is a greenhouse gas. If CO2 is increasing in the atmosphere then its temperature will rise. Temperatures are rising therefore CO2 is causing it.
Really?
Here is the science:
CO2 is a greenhouse gas. It is also a minor greenhouse gas. The most important by far is water vapour.
The earth's atmosphere does not act like a greenhouse. Greenhouses warm by suppressing convection (which is how blankets keep us warm in bed). The supposed effect of carbon dioxide is to slightly reduce the radiation of heat back into space. But most of the energy of the atmosphere is convective, not radiative, so it has nothing to do with a supposed "greenhouse effect"
There is no such thing as a global mean temperature that has physical meaning. The global mean temperature is an index rather like the Dow Jones Industrial Average, it reduces all of the complexity of the real system down to a single number, but it has no fundamental basis in theory. There is no physical theory that gives any basis for something called "mean temperature" in a system which is not at or near equilibrium. In fact, my college physics books state that unless the system is at or near thermal equilibrium (and the Maxwell-Boltzmann relation holds) a temperature does not exist!
The witness of ice core records is all one way - temperatures rise and then six to eight centuries later, carbon dioxide and methane levels rise. But they both don't alter the rate of temperature rise in any measureable way and they continue to rise for centuries after the climate has already begun to cool.
The Hockey Stick (Mann, Bradley and Hughes 1999) has been solidly debunked by multiple independent investigators. Unfortunately the zombie statistical nightmare keeps rising from the dead despite all efforts to impale it as the worthless statistical trash that it is. The latest person to revive the Hockey Stick was Al Gore in "An Inconvenient Truth" - despite mentioning the Hockey Stick as having been attacked by climate skeptics, Gore introduced a new reconstruction to support it which he referred to as "Dr Thompson's thermometer"
which turned out to be the Hockey Stick in disguise. Circular reasoning? Of course.
The interesting thing is that all of the other reconstructions of past climate used by the IPCC also suffer from the same catastrophic statistical failures as the Hockey Stick - they are all junk.
[Aside: and even if they weren't just as bad, they debunk the notion that there is a single variable called "global mean temperature"
A single variable called "global mean temperature"? In your dreams]
The warming of the earth from the Little Ice Age began long before carbon dioxide began to rise in the atmosphere, so we're back to chicken and egg scenario - why did the supposed cause follow the effect by at least 150 years?
Finally, I have not met any scientist who doubts that a) climate changes and b) generally speaking over the 20th Century warming has been seen over most of the Earth. The real climate change deniers are those whose false reconstructions of past climate would lead to the belief that natural climate changes over the last 1-2000 years have been trivial compared to the warming of the 20th Century supposedly by man-made greenhouse warming from carbon dioxide.
