Nick Stokes
The “argument” for AGW, per se, is correct as you stated, with my addition to part 3. (IOW “temperature rise” is already a deduced “consequence”, which may occur unless another compensating “consequence” occurs, for some as yet unknown reason or “natural thermostat” mechanism). As a result, I would also specify that part 3 is a deduced “consequence” of parts 1 and 2.
I would also eliminate the subjective phrase at the end of paragraph 2: “in a big way”.
We then have:
1. GHG’s absorb outgoing IR
2. We are adding GHG’s to the air
3. As a consequence, the increased absorption of outgoing IR means that temperatures will have to rise to restore radiation balance unless other changes, such as increased reflection of incoming SW radiation, compensate correspondingly.
This formulation leaves open whether “temperature rise” could be imperceptible (and hence, insignificant) or perceptible (and hence significant).
The problem is, Nick, that IPCC is selling us a “package”, which speculates that “temperature change” caused by AGW is highly “significant” (compared to that caused by natural forcing) and includes part 4 and 5 as I stated as integral parts.
4. AGW, caused principally by human CO2 emissions, has been the primary cause of observed 20th century warming
5. AGW represents a serious potential threat to humanity and our environment, unless human CO2 emissions can be reduced drastically.
I do not think that you will have many rational skeptics arguing against your 1-3 (with the additions I recommended), however many will object to the IPCC (or “mainstream”) “package”.
Incidentally, that is what is being debated here, Nick, not your parts 1 and 2 plus the modified 3.
Max