How do we know that global warming is due to greenhouse gases?

[The_Flying_Dutchman]

@Sage Rat

Hm, change 30,000 years to 650,000.

According to the report, the historic high point for CO[sub]2[/sub] in the atmosphere is ~300ppm and we’re at 379ppm, where the range was always between 180-300 (120ppm difference), so a 79ppm increase is pretty impressive.

CO[sub]2[/sub] concentration is 379 parts per million?

@Hari Seldon

(They are N2, 78%; O2, 21%; CO2, 1%–the rest are in trace amounts.)

CO[sub]2[/sub] concentration is 10,000parts per million?

Which is correct?

[Q.E.D]

@The Flying Dutchman

Which is correct?

The former.

[placebo]

Gentlemen, please.
Rico has pretty much settled the matter of my user name and I have asked for a name change accordingly. Somehow, I doubt his post was meant to be construed as a mere suggestion. Any and all lobbying on my behalf is of course welcome, but probably belongs in ATMB (or perhaps, the Pit). And since I won’t be subscribing, you won’t have to suffer my presence much longer anyway.

As for my original question, let me restate it once more so that everyone is on the same page. And then answer it myself since I’ve been doing some further reading, in an attempt to forestall the inevitable deluge of contrarian rethoric. See, unlike most responses to this thread so far, my question had a very narrow focus: the 90% figure in that one specific quote. According to these IPCC guidance notes: “[l]ikelihood may be based on quantitative analysis or an elicitation of expert views” and authors should be prepared to explain the latter “by providing a traceable account of the steps used to arrive at estimates of uncertainty or confidence for key findings,” which is all I was asking for in the first place. And though I understand the reflexive need to defend the scientific consensus represented by the IPCC from perceived criticism, please kind in mind that no such criticism has been made on my part, nor is any forthcoming. Unlike “climate skeptics” and similar malcontents, I have enough humility to recognize the extent of my own ignorance.

Anyway, in case anyone is still curious, it turns out that “[t]he approaches used in detection and attribution research […] cannot fully account for all uncertainties, and thus ultimately expert judgement is required to give a calibrated assessment of whether a specific cause is responsible for a given climate change” [AR4 WG1, p. 669].
An account of the thought process involved is also given:

@IPCC

The assessment approach […] is to consider results from multiple studies using a variety of observational data sets, models, forcings and analysis techniques. The assessment based on these results typically takes into account the number of studies, the extent to which there is consensus among studies on the significance of detection results, the extent to which there is consensus on the consistency between the observed change and the change expected from forcing, the degree of consistency with other types of evidence, the extent to which known uncertainties are accounted for in and between studies, and whether there might be other physically plausible explanations for the given climate change. Having determined a particular likelihood assessment, this was then further downweighted to take into account any remaining uncertainties, such as, for example, structural uncertainties or a limited exploration of possible forcing histories of uncertain forcings. The overall assessment also considers whether several independent lines of evidence strengthen a result.