One of the important observations relevant for the hypothetical role of trace gases in the atmosphere is the famous lag.
Lowell Stott, Axel Timmermann, Robert Thunell: "Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO₂ Rise and Tropical Warming"They study isotopes in sediment cores. The main result is that they can reconstruct the following chronology:
- 19,000-17,000 years ago: deep sea temperatures increased by 2 Celsius degrees or so
- 1,000 years later: CO₂ increases
Not only the CO₂ lags by 1,000 years or so but the sea surface temperatures in the tropics lag, too. The deep ocean warmed much earlier than the surface. The authors offer hints that the warm water came there from the South where the primary changes - perhaps "increasing austral spring insolation" - occurred, followed by albedo feedback.
Figure 1: Southern Hemisphere, location of sites. The color indicates the depth of the isopycnal surface (sigma_t = 27.6 kg/m3) in meters
At any rate, if their paper is right, they can rule out not only CO₂ as the cause of the deglaciation but any other mechanism that takes place at the surface or above the surface of the tropical zone (recall that the greenhouse effect should dominate 10 km above the surface in the tropics) as the driver of the deglaciation.
The authors also say a lot of politically correct stuff about the important role of CO₂ that directly contradicts their research but that has allowed them to publish these results in Science. The lead author argues that he doesn't want want people to think that CO₂doesn't drive the climate: it's just not the beginning, [the bulk,] and the end of it. ;-)
See also: USC press release
Hat tip: Marc Morano