What happened the last time global temperatures rose by 8 degrees Celsius?


Look at the map of the Eocene world above.  Isn’t it beautiful?  Europe separated from Asia by a sea boundary.  Australia blissfully isolated.  Antarctica is looking lush.  South Americans will make their own jokes about the gulf in the north west of their continent; I’m unfamiliar with their rivalries.  The Muslim world is almost entirely submerged.  No sea appears between Mexico and the US, however.  You can’t have everything.

Anyway, world leaders have pledged to prevent average global temperatures rising by more than 2 degrees Celsius.  What would happen if temperatures went higher than this?

The last time we had a really hot spell was during the Paleocene-Eocene Thermal Maximum (PETM) perhaps 55 million years ago.  That’s about 10 million years after the dinosaurs had shuffled off the mortal coil.

The PETM was probably caused by natural releases of carbon or other warming gasses.

So what happened next?  Did the world burn?  Did anything survive?

Well, the world got wetter, especially away from the equator.  Sea levels rose.  This was because of thermal expansion rather than melting ice because at the start of the period, there wasn’t much ice to melt anyway.

But what about mass extinctions, you ask?  No one wants to go extinct.  Except for greenies like this lot.

Well, it was bad news if you were foraminifera living in seafloor sediment.  Stacks of them died off even after they’d just survived the dinocaust.  Other types of foraminifera did well, as did some plankton.  But I don’t know how many of my readers are foraminifera or plankton.  An intellectuable blog like this tends to attract higher life forms, like mammals.  So how did they go?

Well they did pretty well.  Many new species appeared and spread, including horses, the ancestors of other hooved animals, and those pesky primates.  That’s our mob!

It wasn’t a mass extinction event, although there was a minor one around 20 million years later when atmospheric carbon dioxide and temperatures declined.

On the other hand, the PETM changes occurred more slowly than those of today, giving species a better chance to adapt.  Also, various factors differ today such as the position of the continents, the direction of currents, Earth’s orbit, the existence of ice sheets etc., etc.

So what would happen if, say, the climate rose rapidly by 5 degrees before we sorted out technological solutions to today’s energy problems and the subsequent feedback loops?  Perhaps flooding in some low lying areas.  Increased rainfall and therefore agricultural output in others, if we’re still physical beings that eat food by then.  Tropical diseases that haven’t been cured spreading away from the equator.  Maybe an increased rate of extinction until adaptation leads to a bounce back in biodiversity.  It doesn’t look like a mass extinction event.  Of course, I don’t know. Nor do I care.

I don’t have kids.

And to those future human-like creatures eking out a miserable existence in that possibly hellish landscape, who have discovered my article in some relic of the internet, who are hating my indifference to the destruction of their world – why should I care what you think.  What have you ever done for me?


Further reading:  How the world will really end

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