"The data show that the Earth’s climate was on a long cooling trend in the Paleocene, associated with removal of CO2 from the atmosphere and burying it in sediments, deposits of peat, permafrost and methane hydrates. Those carbon reserves were like deposits in a bank account – available for withdrawal later. The first signs of warming began around 58.9 million years ago associated with a sharp jump in ocean bottom water temperatures (known as the “ELPE” - Early Late Paleocene Event), followed 1.2 million years later by a more steady warming trend that underpinned regular cycles of hotter and cooler climate (those hot flashes that we call Hyperthermals).
The clue is in the regularity of the fluctuations.
Scientists combined radiometric dates on volcanic ash layers with the record of Earth’s magnetic reversals and the known cycles in Earth’s orbit, to correlate the sedimentary records at the different locations. This also allowed a mathematical assessment of the correlation between the climate cycles recorded in sediments and Earth’s orbital cycles. There are 3 different kinds of orbital cycle that control the intensity of sunlight on Earth (solar insolation): eccentricity, precession, and obliquity – for more about them see this post.
The 3 papers show that the Hyperthermals and their effects were global, and were paced by orbital eccentricity on cycles of 405,000 and 100,000 years, and also by orbital precession (21,000 year cycles). The longer eccentricity cycles are associated with ocean bottom water temperature swings of up to 2-4°C (4-7°F), while the 100,000 year cycles correspond with 1.5°C (3°F) swings in bottom temperature. There’s very little contribution from the obliquity (41,000 year cycle) probably because there was very little ice at the poles at the time (unlike during the Pleistocene ice age, when obliquity was much more prevalent).
In the oceans these cycles show up as regular variations in carbon isotope ratios (reflecting carbon cycle changes) and oxygen isotope variations (reflecting ocean temperature) and the proportion of “Coarse Fraction” or Iron intensity in sediments (reflecting carbonate dissolution and sediment supply).
"This new thinking is supported by Smith et al, who concluded that the regular carbon releases in the Eocene Hyperthermals:
“...were the effect rather than the cause of global paleoclimatic and geomorphic changes during the EECO.” (my emphasis)
Littler et al’s study would seem to concur. They found that ocean bottom temperatures lead the carbon cycle by around 6 millennia for the 405,000 year cycles (less in the Paleocene, more in the mid Eocene) and about 3,000 years for the 100,000 year cycles. This indicates that the ocean carbon signal in orbitally-controlled climate change is a feedback response to orbitally-driven temperatures.
In contrast, today’s climate change is not orbitally-driven – if it were we would be experiencing global cooling, not warming. It has also taken place in a time frame just 3% of even the fastest orbital cycle.
"As was the case during the Paleocene, our modern Earth has reserves of permafrost and methane hydrates that were ‘banked’ during the cool Pleistocene ice age all the way up to the pre-industrial era. And even though some interglacials may have been warmer than the preindustrial era, deep-ocean temperatures appear to have been only slightly elevated, keeping most deep sea methane locked away - until now. A Paleocene-to-Eocene-like methane release is expected from modern climate change because the deep oceans are now warming by a magnitude unprecedented in the past several million years!
Last year Zeebe and Zachos compared the long tail of the PETM with our present human-caused global warming. They concluded that our own long hot tail will last tens of thousands to hundreds of thousands of years. But they argued that future environmental effects will:
“more likely resemble the end-Permian and end-Cretaceous catastrophes, rather than the PETM,”
due to the far more abrupt nature of modern carbon emissions and warming."http://www.skepticalscience.com/long-ho ... ocene.html
So I guess I am just an "envirometalist" like Milton B thinks.