The powerful role of carbon dioxide as a regulator of Earth’s climate over deep history is further exposed in an analysis of ancient algae found buried in seabed cores. It reveals that a drop in atmospheric carbon dioxide of about 40 per cent appears to have been the driving force behind the formation of the Antarctic ice sheet 34 million years ago, say US scientists at Yale and Purdue universities in a paper in Science … While the study sheds new light on the consequences of a moment one scientist described as ”the mother of all climate tipping points”, the factors that drove the fall in carbon dioxide levels remain a mystery.
I was just wondering if anyone here has any insight into what might have caused such a drop in carbon dioxide levels. Thanks!
Jerry McManus @1 — Carbonization, i.e. weathering, removed more CO2 than vulcanism added, on average, for the past ~50 million years [since the mid-Eocene epoch]. The rise of the Himalayas is implicated but for another interpretation see http://en.wikipedia.org/wiki/Eocene
Comment by David B. Benson — 9 Dec 2011 @ 10:31 PM
#1 Jerry McManus,
It was theorized years ago that the formation of the Himalayas might have supercharged the weathering process which allows CO2 to be removed from the atmosphere on geological timescales. In that case the process would even now allow faster CO2 removal than 50+ million years ago. I don’t know if that theory has been discredited.
Comment by Anonymous Coward — 9 Dec 2011 @ 11:19 PM
“simply demonstrating that the original claim was made up”
Roger that. How do you deal with characters like wmar on dotearth who make up lies apparently straightfaced?
Not wanting to get into a flame war, just calling wmar a liar isn’t going to work anyway. How do you demonstrate?
Comment by Edward Greisch — 10 Dec 2011 @ 12:51 AM
I just checked, and now the Russians have posted information about their conference. Maybe some scientists were at your meeting who also attended the Russian conference. You can find the papers here if you check around. http://www.pacc2011.ru/
I watched Dr. Santer’s talk, and was a bit surprised when he recounted that at a recent hearing, he was told that climate scientists don’t investigate “skeptical” viewpoints. That is just…words fail here.
Incidentally, does anyone know if Dr. Schneider did some birding trips to Point Pelee in the the late 80s to early 90s? When I was there I’d look for people who seemed to know what they were doing so I’d start tagging along, staying in the background and listening/watching. One person noticed me lurking on the edge of the group and started directing comments, explanations to me. I probably learned half as much in that one day as I had in the past two years. In biased memory retrospect that person looked similar to Dr. Schneider, and he was certainly was a thoughtful enlightening communicator.
Comment by Daniel J. Andrews — 10 Dec 2011 @ 11:14 AM
Don’t post this–just a question.
I linked to Hansen’s powerpoint on comment 4 in a post I made about Hansen’s presentation. However, it seems like I could change the slides on that powerpoint. It’s not the show version. Could someone change his powerpoint and then post something different?
I would like to link, but shouldn’t it be something I (or someone else) can’t change?
Jerry McManus @ 2, You may be mystified by David’s answer to your question. What the heck does the rise of the Himalayas have to do with it?
Your question involves
1) the slower geological part of the global carbon “cycle”. This long term process is rock weathering, especially silicate rocks slowly dissolving in carbonic acid (CO2 + rain water) and converting to sand (SiO2) and carbonate rocks, mainly CaCO2. This steadily reduces atmospheric CO2 content, which is replaced by outgassing from volcanoes. When plate tectonics leads to a crash and the rise of a new mountain range, the near-vertical rock surfaces have more area than a flat expanse would have and so rock weathering speeds up, thus the reference to the rise of the Himalayas. When there is high CO2 in the air silicate weathering also naturally speeds up. This slow process has gradually reduced atmospheric CO2 for millions of years although there are ups and downs of CO2 concentration along the way.
2) Orbital forcing – (Milankovic cycles) may have helped start the icing of Antarctica.
3) The opening and then deepening of the Drake Passage, which leads to a distinct and very cold Southern Ocean circulating around Antarctica. This inhibits the southward transfer of heat from the tropics.
“The idea that falling CO2 facilitated the growth of the Antarctic ice sheet is not new. But as the paper says
“Published CO2 reconstructions provide contradictory
evidence for the role of CO2 during high latitude
cooling and Antarctic ice sheet expansion,….”
This paper advances our understanding of the subject by finding a sharper way to make use of various “proxies” that indicate things like past CO2 concentration and temperatures. This may be the paper’s main contribution to ongoing research. Treating the Drake Passage as open but shallow also helps to resolve things. As a result, the CO2 concentration associated with the growth of the ice sheet is pinned down better than it was before.
Comment by Pete Dunkelberg — 10 Dec 2011 @ 2:54 PM
Pete Dunkelberg @ 15
Thanks for the thoughtful and detailed reply, very interesting! As a layman I do have a rudimentary understanding of C02 sequestration from rock weathering, so the Himalayas reference made sense, at least on a geologic time scale.
Speaking of which, this bit from James Hansen is especially, um, timely:
The human-caused release of increased carbon dioxide into the atmosphere also presents climate scientists with something they’ve never seen in the 65 million year record of carbon dioxide levels — a drastic rate of increase that makes it difficult to predict how rapidly Earth will respond. In periods when carbon dioxide has increased due to natural causes, the rate of increase averaged about .0001 parts per million per year — in other words, one hundred parts per million every million years. Fossil fuel burning is now causing carbon dioxide concentrations to increase at two parts per million per year.
“Humans have overwhelmed the natural, slow changes that occur on geologic timescales,” Hansen said.
Comment by Pete Dunkelberg — 11 Dec 2011 @ 11:32 AM
Is there a report of Igor Semiletov’s talk or of the response? According to The Independent, Semiletov presented findings from his (and others’) recent expedition to the East Siberian Arctic Shelf to update our knowledge about methane released there.
According to recent Russian observations of multiple new kilometer wide methane plumes, which are exhausting directly to atmosphere, it appears abrupt global climate destabilization may have begun. Warming Siberian clathrates may even be destabilizing not only from carbonic acid gas radiative forcing causing destruction of floating Arctic sea ice but from increasing tectonic activity which may be allowing the planet’s molten hot mantle easier access to crustal fissures across the sea beds. This appears to be due to trillions of tons of regional off-loading of solid water from polar lands from the observed increasing warmth and resultant hydrology phase change.
Philosophically speaking from this rather discouraging perspective, modern man’s definition of lithosphere matter as “energy” may be the fundamental folly initiating a sixth extinction. Yet, it may come to pass that the planet’s automatic response to massive carbonic acid contamination (from igniting sequestered, geologic, lithosphere carbon) will be precipitated instead by (hundreds of billions of tons of) methane exhaust.
Geoengineering indeed. Wish those Ruskies would stop poking around what’s left of the “permafrost.” Not that this is a “national security” issue or anything.
Comment by Solar Jim Newberry — 14 Dec 2011 @ 12:43 PM