Messing with the PETM

PETMLiving a hour out of town, I quite often listen to podcasts in my car, and particularly like the BBC Radio 4 programme In Our Time, in which Melvyn Bragg interviews experts on a variety of topics from culture, to history, to philosophy, to science etc. A recent programme was on the Paleocene-Eocene Thermal Maximum, which is when the planet got about 5° hotter than normal about 50 million years ago. There is a useful summary at Seven things that happened when the planet got really, really hot and the podcast itself can still be downloaded.

There are lots of interesting things to say about the PETM, and Melvyn’s guests said quite a lot of them, but the programme was somewhat marred by the climate change claptrap that seems to permeate everything these days.  The real scientific reality is that the cause of the PETM is unknown[1], but this gets translated into Flopsy as “The cause of the PETM must have been carbon dioxide, but the cause of the carbon dioxide is unknown”.[2]

One of the interesting things about the PETM is that it was a good thing. Rapid global warming (much more pronounced than anything on the cards today) produced an explosion of evolution, including the evolution of our own ancestors. And so, without that period of rapid global warming, it is far from clear that we would even exist. And so it fits into the pattern like this:

  • the Medieval warming period was warmer than today, and coincided with a great flourishing of humanity.
  • The Roman warming period was even warmer than the Medieval warming period, and coincided with a great flourishing of humanity;
  • the Minoan warming period was even warmer than the Roman warming period, and coincided with a great flourishing of humanity;
  • the PETM was even warmer than the Minoan warming period, and coincided with a great flourishing of mammals generally.

Thus the actual evidence – that global warming is a good thing – goes back a very long time. Not that we are seeing much of it at the moment. Carbon dioxide levels in the atmosphere are continuing to rise, which is excellent news for the planet because it is providing a much-needed boost in vegetation. But the temperatures are not following along in the way that the Flopsy’s have predicted.

Winter is coming.





[1] A recent note on the topic by Javier includes this:

A very big assumption underlies the 2010 Statement and 2013 Addendum by the Geological Society of London. And in science assumptions are very dangerous, because they are not subjected to the scientific method. The big ugly assumption in these reports is that past changes in CO2 were responsible for planetary temperature changes. At most, what we can extract from past data is a correlation between both, and even that correlation is tentative, as the quality and nature of the data makes any conclusions in the statement and addendum questionable.

We do know that temperature affects CO2 levels, as an increase in temperature leads to a release of CO2 by the oceans, due to the gas solubility dependence on temperature. So, the causality is confusing. Is the CO2 mainly the result of temperature changes or is the temperature mainly the result of CO2 changes? We don’t know.


[2] To be fair, one of the experts was a bit more honest, in identifying sotto voce that it was methane, not carbon dioxide, that was so abundant at the time of the PETM. Methane does, of course, contain carbon, but it is not the same as carbon dioxide. Why did they repeatedly say “carbon” and not “methane”? It was surely to try to associate what happened 50 million years ago with the absurd predictions being made today.


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