Dr Andrew Glikson: Human evolution and the atmosphere: return to the Pliocene?

Scroll down and open the attachment (be patient, it takes only a few moments), a brilliant power point lecture by Earth and paleoclimate scientist Dr Andrew Glikson (Australian National University, Canberra, Australia) illustrating the global temperature, methane and CO2 levels in the generally cooling period since the Pliocene (3 Mya, million years ago) during which time the genus Homo evolved to yield Homo sapiens (us) about 100,000 years ago. However, massive man-made greenhouse gas (GHG) pollution in the industrial era (post-1750) has pushed atmospheric CO2 concentration  outside the  range of 180-300 ppm obtaining during the final evolution of Homo sapiens from his immediate precursors .

The thrust of the lecture is succinctly summarized by the title of the lecture: "Human evolution and the atmosphere: return of the Pliocene?"

While atmospheric CO2 concentration varied between 180 and 300 ppm over the last 400,000 years, in the last 50 years we have gone outside this zone with CO2 currently at 387 ppm (as compared to the pre-industrial of about 280 ppm) and First World governments are evidently sanguine about increasing this to a catastrophic 450 ppm.

Dr Andrew Glikson (an Earth and paleo-climate research scientist at Australian National University, Canberra, Australia) has summarized the problem in  “The Methane Time Bomb and the Triple Melt-down" on Countercurrents, 10 October 2008 (see: : http://www.countercurrents.org/glikson101008.htm ): For some time now, climate scientists warned that melting of subpolar permafrost and warming of the Arctic Sea (up to 4 degrees C during 2005–2008 relative to the 1951–1980) are likely to result in the dissociation of methane hydrates and the release of this powerful greenhouse gas into the atmosphere (methane: 62 times the infrared warming effect of CO2 over 20 years and 21 times over 100 years) The amount of carbon stored in Arctic sediments and permafrost is estimated as 500–2500 Gigaton Carbon (GtC), as compared with the world’s total fossil fuel reserves estimated as 5000 GtC. Compare with the 700 GtC of the atmosphere, which regulate CO2 levels in the range of 180–300 parts per million and land temperatures in a range of about – 50 to + 50 degrees C, which allowed the evolution of warm blooded mammals. The continuing use of the atmosphere as an open sewer for industrial pollution has already added some 305 GtC to the atmosphere together with land clearing and animal-emitted methane. This raised CO2 levels to 387 ppm CO2 to date, leading toward conditions which existed on Earth about 3 million years (Ma) ago (mid-Pliocene), when CO2 levels rose to about 400 ppm, temperatures to about 2–3 degrees C and sea levels by about 25 +/- 12 metres. There is little evidence for an extinction at 3 Ma. However, by crossing above a CO2 level of 400 ppm the atmosphere is moving into uncharted territory. At this stage, enhanced methane leaks threaten climate events, such as the massive methane release and fauna extinction of 55 million years ago, which was marked by rise of CO2 to near-1000 ppm.”

We are very grateful to Dr Andrew Glikson for permitting Yarra Valley Climate Action Group to place his brilliant power point lecture on its website.


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Gideon Polya,
May 26, 2009, 11:51 PM
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