Extreme Temperature Diary- December 16th, 2018/ Topic: Climate Heading Back To The Eocene?

Sunday December 16th… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)😊. 

Climate Heading Back To The Eocene?

Yesterday we delved into a past epoch, the Pliocene, which had carbon levels in the atmosphere roughly like that of the current day. What might happen to the climate say if we kept the dreaded “business as usual” scenario? My good friend Scott Cook passed along the following chart to give the answer (from: https://documentcloud.adobe.com/link/track?uri=urn:aaid:scds:US:b08a2b3b-acff-492f-be5c-f89dfc9603a0)

We can learn a lot from this chart. Let’s suppose that the level of carbon in the atmosphere busts through the 500 parts per million stat moving up and up such that the global mean temperature gets to +5C by 2100 and even +10C before the year 2200, putting humanity’s civilization and even the species itself in danger of disappearing off the face of Earth. Looking at the above chart the most comparable geologic era with that warm of a range of temperatures would be the Eocene, the period just after the disappearance of the dinosaurs due to an extinction level impact event about sixty million years ago, well before the advent of man’s distant private relative ancestors began to evolve. At +10C above preindustrial conditions there would be an ice free Earth, so sea levels would be at maximum,  80 feet above current levels. Welcome to a new Atlantis if civilization sees an ice free Earth.

What’s also noticeable is that the planet has had a slow cooling trend since the Eocene up until ten thousand years ago allowing for the advent of agriculture and civilization. We are currently in a natural interglacial period which many climatologists say is just about to end if it weren’t for carbon pollution. I do think that carbon pollution has saved civilization from being hurt from a new freezing glacial period looking at what was beginning to happen after the medieval warm period, but it’s about to get way too hot for comfort.

Just like we did yesterday with the Pliocene let’s see what a strange world the Eocene was compared to that of today: https://en.wikipedia.org/wiki/Eocene

Quoting Wikipedia:

The Eocene ( /ˈəˌsn, ˈ-/[2][3]) Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. The end is set at a major extinction event called the Grande Coupure (the “Great Break” in continuity) or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified,[4] though their exact dates are slightly uncertain. 

The Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Palaeocene–Eocene Thermal Maximum (PETM) at 56 million years ago to a maximum during the Eocene Optimum at around 49 million years ago. During this period of time, little to no ice was present on Earth with a smaller difference in temperature from the equator to the poles. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene-Oligocene transition at 34 million years ago. During this decrease ice began to reappear at the poles, and the Eocene-Oligocene transition is the period of time where the Antarctic ice sheet began to rapidly expand. 

Greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature. The end of the PETM was met with a very large sequestration of carbon dioxide in the form of methane clathrate, coal, and crude oil at the bottom of the Arctic Ocean, that reduced the atmospheric carbon dioxide.[7] This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, and it is hypothesized that the sequestration was mainly due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion on how much carbon dioxide was in the atmosphere. This is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm[8] while other proxies such as pedogenic (soil building) carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years.[9] Sources for this large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from the PETM event in the sea floor or wetland environments.[8] For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. 

The middle to late Eocene marks not only the switch from warming to cooling, but also the change in carbon dioxide from increasing to decreasing. At the end of the Eocene Optimum, carbon dioxide began decreasing due to increased siliceous plankton productivity and marine carbon burial.[8] At the beginning of the middle Eocene an event that may have triggered or helped with the draw down of carbon dioxide was the Azolla event at around 49 million years ago.[13] With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, which is a floating aquatic fern, on the Arctic Ocean. Compared to current carbon dioxide levels, these azolla grew rapidly in the enhanced carbon dioxide levels found in the early Eocene. As these azolla sank into the Arctic Ocean, they became buried and sequestered their carbon into the seabed. This event could have led to a draw down of atmospheric carbon dioxide of up to 470 ppm.[13] Assuming the carbon dioxide concentrations were at 900 ppmv prior to the Azolla Event they would have dropped to 430 ppmv, or 30 ppmv more than they are today, after the Azolla Event. Another event during the middle Eocene that was a sudden and temporary reversal of the cooling conditions was the Middle Eocene Climatic Optimum.[14] At around 41.5 million years ago, stable isotopic analysis of samples from Southern Ocean drilling sites indicated a warming event for 600 thousand years. A sharp increase in atmospheric carbon dioxide was observed with a maximum of 4000 ppm: the highest amount of atmospheric carbon dioxide detected during the Eocene.[15] The main hypothesis for such a radical transition was due to the continental drift and collision of the India continent with the Asia continent and the resulting formation of the Himalayas. Another hypothesis involves extensive sea floor rifting and metamorphic decarbonation reactions releasing considerable amounts of carbon dioxide to the atmosphere.[14] 

At the end of the Middle Eocene Climatic Optimum, cooling and the carbon dioxide drawdown continued through the late Eocene and into the Eocene-Oligocene transition around 34 million years ago. Multiple proxies, such as oxygen isotopes and alkenones, indicate that at the Eocene-Oligocene transition, the atmospheric carbon dioxide concentration had decreased to around 750–800 ppm, approximately twice that of present levels.[16][17]

Here is an artist’s rendition of some of the flora and fauna from the Eocene:

I abbreviated the Wikipedia article on the Eocene, which I invite all to read in its entirety or, of course, other in depth material. Certainly even in a very warm climate flora and fauna flourished looking at the fossil record. It’s my learned opinion that humans could adapt, but conditions would be harsh with much storminess and high precipitation rates to contend with in non-desert areas. Humans could learn to devour and cultivate any vegetation that could adapt, but there are many unknowns here…that is if we can rebuild inland after a well more than 20 foot sea level rise.

The Eocene serves as a warning to those thinking that continued burning of fossil fuels won’t have severe consequences. This is hard science folks. learn from it.


Here is some of Sunday’s other weather and climate news:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity.)

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The Climate Guy

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