Graph of the Day: Scientific American on Today’s Greenhouse vs. History – the PETM
June 29, 2011
PETM, the Paleocene – Eocene Thermal Maximum.
That’s the last time in earth history that things changed in a way similar to the way they are changing now. It was 55 million years ago, give or take a millenium.
Scientific American (sub required – you can also buy single issues) has an article by one of the real experts, Lee Kump, comparing the pace at which the earth changed during the most recent Great Warming event. As the sobering graph shows, the current CO2 buildup is prodeeding at a blistering pace compared to the ancient past. Current rates of change are thousands of times faster than normal, and even 10 times faster than one of the most spectacular geological changes in the record.
The PETM bears some striking resemblances to the human-caused climate change unfolding today. Most notably, the culprit
behind it was a massive injection of heat-trapping greenhousegases into the atmosphere and oceans, comparable in volume to
what our persistent burning of fossil fuels could deliver in coming centuries….. New answers provide sobering clarity. They suggest the consequences of the planet’s last great global warming paled in comparison to what lies ahead, and they add new support for predictions that humanity will suffer if our course remains unaltered.
According to Kump:
..Today investigators think the PETM unfolded something like this: As is true of our current climate crisis, the PETM began, in a sense, with the burning of fossil fuels.
At the time the supercontinent Pangaea was in the final stages of breaking up, and the earth’s crust was ripping apart, forming the northeastern Atlantic Ocean.
As a result, huge volumes of molten rock and intense heat rose up through the landmass that encompassed Europe and Greenland, baking carbon-rich sediments and perhaps even some coal and oil near the surface. The baking sediments, in turn, released large doses of two strong greenhouse gases, carbon dioxide and methane.
Judging by the enormous volume of the eruptions, the volcanoes probably accounted for an initial buildup of greenhouse gases on the order of a few hundred petagrams of carbon, enough to raise global temperature by a couple of degrees. But most analyses, including ours, suggest it took something more to propel the PETM to its hottest point.
When the gas releases began, the oceans absorbed much of the CO2 (and the methane later converted to CO2). This natural carbon sequestration helped to offset warming at first. Eventually, though, so much of the gas seeped into the deep ocean that it created a surplus of carbonic acid, a process known as acidification.
Moreover, as the deep sea warmed, its oxygen content dwindled(warmer water cannot hold as much of this life-sustaininggas as cold water can). These changes spelled disaster for certain microscopic organisms called foraminifera, which lived on the sea floor and within its sediments. (the whitish colored sediment at the bottom of the core here – PS) The fossil record reveals their inability to cope: 30 to 50 percent of those species went extinct.
The message of the graph, and the core, are clear. We are changing the planet at a rate unprecedented outside of the most severe convulsions the planet has seen in 4 billion years of history. We do not know what the results will be.
I don’t think I want my children and grandchildren to find out.
In the video below, James Hansen’s abbreviated lecture on paleo-history since the PETM.