50 million years ago

The Daily Mail has carried an article which says that:

Scientists today announced that levels have reached record highs of 410 parts per million which could snowball over the coming years causing global catastrophe.

If the trend continues experts say by 2050 we will have levels of carbon dioxide in the atmosphere that have not been seen for 50 million years.

By 2050? Despite all observed warming being consistently less than IPCC estimates, let us just take this fable for truth, shall we? Let us just ignore how much ice there is still to melt in Greenland and Antarctica, and contemplate what it was like when the earth was much warmer than it is now.
How hot was in back there in the Eocene era? And how much CO2 was in the atmosphere?

The graph above serves as a proxy for what has happened to the earth’s climate, though it measures only polar ocean conditions. It immediately establishes on gigantic fact, that they do not tell you about in newspapers.

The world has been getting colder for about 50 million years.

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[7] 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.[8] 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 (Paleocene- Eocene Thermal Maximum) event in the sea floor or wetland environments.[7] For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%.
When was this thermal maximum? According to Wikipedia, 49 million years ago. Close enough to 50 million for the purposes of the discussion.
What were the conditions at this thermal maximum?

The poles were largely or completely ice-free.There was little or no glaciation anywhere.

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.[7] 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.[12] 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.[12] 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
Thus, plant life in polar oceans caused a sequestration of carbon dioxide, thus reducing temperatures.

Another event during the middle Eocene that was a sudden and temporary reversal of the cooling conditions was the Middle Eocene Climatic Optimum.[13] 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.

Six hundred thousand years – longer than there have been anatomically modern humans. We only left Africa 50-30 thousand years ago.

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.[14] 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.[13]

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.[15][16]

Observe that, in conditions utterly without human influence, CO2 levels were ten times what they are now, and then reduced by natural actions to twice what they are now.

The article also shows that fossils of cold intolerant reptiles and tropical plants have been found in the high Arctic. Axel Heiberg Island is possessed of a large petrified coniferous forest. Imagine feathered dinosaurs stomping about in polar darkness through sequoias and palm trees.

Again from the Wikipedia entry on Axel Heiberg island:

Over 40 million years ago during the Eocene era, a forest of tall trees flourished on Axel Heiberg island. The trees reached up to 35 metres in height; some may have grown for 500 to 1,000 years. At the time, the polar climate was warm, but the winters were still continuously dark for three months long. As the trees fell, the fine sediment in which the forest grew protected the plants. Instead of turning into petrified “stone” fossils, they were ultimately mummified by the cold, dry Arctic climate, and only recently exposed by erosion.[7]

Alas, this happy story of a warmer earth comes to an end about 49 million years ago>

The Eocene is not only known for containing the warmest period during the Cenozoic, but it also marked the decline into an icehouse climate and the rapid expansion of the Antarctic ice sheet. The transition from a warming climate into a cooling climate began at ~49 million years ago. Isotopes of carbon and oxygen indicate a shift to a global cooling climate.[12] The cause of the cooling has been attributed to a significant decrease of >2000 ppm in atmospheric carbon dioxide concentrations.[7

Further information on the fascinating subject of how it was so warm and got so cold can be found in the Wikipedia article on the Paleocene-Eocene thermal maximum (PETM) which is a Big Deal in for scientists seeking to understand that earth’s history and the relationship of CO2 concentrations to climate change.

Sequoias on Axel Heiberg island? Alligators in Great Slave lake? Maybe in 20,000 years. Or maybe, as is more likely, we shall have ice sheets covering North America as far south as Manhattan.  Remember, Long Island, Martha’s Vineyard, and Nantucket are the moraines left by continental ice sheets that covered our country until a trivial 11,000 years ago.

Are we about to resume global cooling as this current interglacial comes to an end in a couple of thousand years, or next winter?

Or will we see heat such as we have not seen since the middle of the Eocene?

The earth has survived both extremes.




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