Wednesday, July 24, 2013

That Was Then, And This Is Now: The Paleocene-Eocene Thermal Maximum And What It Means To Us!

The Paleocene Epoch was the first epoch in the Cenozoic Era, which is the period including everything from the end of the Cretacious (extinction of the dinosaurs) to the present. As a point of note, this period includes the Tertiary and Quaternary. These two sub-periods of the Cenozoic are distinguished in time by the sequences of fossils present in rocks from these periods. There is further subdivision of the Tertiary into the Paleocene, the Eocene, the Oligocene, the Miocene, and the Pliocene, which  were distinguished by an even finer grading of the fossils present. The first epoch coming at the end of the Cretaceous Era was the Paleocene Epoch, followed by the Eocene, and then the Oligocene. These three make up the Paleogene, or the “old” period of the Cenozoic. (1)  The subject of this post is that period transitioning from the Paleocene to the Eocene during which an event referred to as the Paleocene-Eocene Thermal Maximum occurred (sometime referred to by its acronym, PETM – also known in some literature as the LPTM for Late Paleocene Thermal Maximum).

The PETM event is significant because it was the last significant instance of serious global warming before what we are now experiencing. During this period the mean temperature of Earth’s oceans are estimated to have risen as much as 41 degrees Fahrenheit over a 20,000 year period. (2) As noted by the researchers in this study, pinpointing the cause of the PETM requires extremely accurate dating of the event so that it can be correlated or disassociated from other precisely calculated events of Earth’s past such as the peak of a Milankovitch Cycle or other known events. Based on their research, the most exact date span to date has been generated - between 55.728 and 55.964 million years ago. The significance of this is that it places the event outside the timing of a Milankovitch cycle and reinforces the notion that what we know as greenhouse gases were probably the root cause. 

                We all know about CO2 and its effect as a greenhouse gas (GHG). People frequently overlook, or are simply unaware, of the significance of methane as a GHG. Methane is estimated to be 20 times more potent as a greenhouse gas than CO2 and there are huge quantities of it naturally sequestered on the ocean floor and the continental shelves facing the North Pole in the form of methane hydrate (note the red dots not on land in the Arctic region - basically ALL of the Arctic).(3)

The map shown above indicates where known deep sea and continental shelf deposits are located. Red dots indicate areas where it is considered highly likely that methane hydrate will be found in large quantities, yellow dots indicate areas that have proven to have large quantities.  Note a number of locations in the Arctic continental shelf areas, with more having been discovered since this map was generated. Virtually every red dot on this map has been proven to have large methane hydrate reserves in the period since 2005, when the data for this map was published.

                Methane hydrate is basically a pentagonal ice crystal with a methane molecule trapped in the middle. It is stable as a result of pressure and/or temperature – high pressure and/or low temperature. It would take a serious change in the processes that we are familiar with today in terms of ocean cycles, and the hydrologic cycle in general, to disturb most of those methane hydrate deposits… except for the methane hydrate on the Arctic continental shelves.(4) The methane trapped there (900+ gigatons) is not in deep ocean so the only thing that keeps it  stable as methane hydrate is temperature.(5) The cold necessary for hydrate stability was routinely a function of a thick covering of arctic sea ice, which is now gone.  Original predictions associated with global warming had complete disappearance of summer Arctic sea ice occurring by mid century. The latest estimates have it occurring by the summer of 2015.(6,9)  The MOST recent reporting indicates a massive melt off has occurred early this year. (7) 

            The significance of all this is relatively straight forward. Based on careful work done by scientists studying the Paleocene-Eocene Thermal Maximum they have been able to model an effective cause for the PETM event – the abrupt release of methane into the atmosphere, probably from methane hydrate in the ocean, due to a sudden shift in ocean warming. (8) Any number of things could cause a sudden shift in ocean warming, but their notions of the time frame for the PETM event are around ten thousand years, and the abrupt release could have been over tens of years. 

            We have a scenario where we are on the doorstep of several significant factors in oceanic warming in the Arctic colliding in space and time – loss of sea ice in the summer, significantly increased absorption of sunlight by the Arctic ocean, general conditions of global warming and significant increases of methane release already documented in the Arctic. Is there any reason to think that these combined conditions won’t change any number of other things related to global warming and climate change? No. Is there any reason to think that the aggregate set of conditions won’t create sudden and serious changes in lower depth water temperatures? No. 

             Welcome to the Paleocene-Eocene Thermal Maximum - Take 2… only this time it won’t take thousands  of years to peak because we face the probability of the abrupt release of 900+ gigatons of methane hydrate into the atmosphere of the Arctic over a matter of months and years, not decades and centuries… which (if you’ll pardon the pun) has, quite literally, explosive potential for harm. Imagine something that gets out of control in a few years and takes a hundred thousand years to rebalance, something that is SO sudden that nothing has time to adapt...

  1.     The Cenozoic Era
  2. Charles, A. J., Condon, D. J., Harding, I. C., Pälike, H., Marshall, J. E. A., Cui, Y. & Kump, L. Constraints on the Numerical Age of the Paleocene-Eocene Boundary. Geochemistry Geophysics Geosystems 12, Q0AA17, doi:10.1029/2010GC003426
  3. Hester, K.C. Brewer, P.G., Clathrate Hydrates In Nature, 2009, Annual Review Of Marine Science
  8. Gerald R. Dickens, Maria M. Castillo and James C. G. Walker, A Blast of Gas in the Late Paleocene: Simulating First Order effects of Massive Dissociation of Oceanic Methane Hydrate; Geology 1997;25;259-262
  9.   Arctic Methane: Why The Sea Ice Matters

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