- The greenhouse effect is real, and is what keeps the Earth's average temperature at +15*C instead of -15*C. Geophysical fact.
- CO2 is a greenhouse gas. Textbook physical fact, like water freezes at 0*C.
- CO2 has increased by 41% since we started burning fossil fuels. Observed fact.
- A doubling of CO2 will, when things settle down, cause an increase of ~1*C in global temperatures. (physical calculation).
- This increase is expected to cause a 3*C+ increase in global temps due to positive feedbacks
That's it. It's as simple as that. 1-4 are scientific certainties, and I would dare to say that anyone who tries to debate them is a) a timewaster and b) is in denial.*
I try not to debate with deniers, because it is a waste of time. I am happy to debate 5, because that is where the scientific debate is at. The consensus view is as above, around 3*C and the skeptic hypothesis is that climate sensitivity is low, about 0*C. This hypothesis is refutable, and should be debated briskly and universally, so that we can get the "skeptic" hypothesis out of the way and get on with decarbonising the world economy, and also reforesting the earth.
* I'm sorry, I know this causes offence, but denial is a psychiatric diagnosis, and I am a psychiatrist, so I am allowed to give this as my opinion, even though many "skeptics" believe it to be politically incorrect. Pat Michaels is a major skeptic, and he says that people who deny that CO2 will cause warming are "nutters", which is worse than describing them as being in denial.