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Most pessimistic scenarios about climate change predicts a global rise of temperature of several Celsius degrees over the course of the 21st century if no action is taken. While such a shift in temperature has many implications such as rising seal levels (due to the melting of ice near the poles) and a mass extinction event, the Earth has recordedly had eras warmer than today in the past, such as the Cretaceous period. For reminders, Cretaceous is the last geological period before the extinction of dinosaurs, and it had notably higher sea levels and a warmer global surface temperature (4 °C above today's average surface temperature).

Assume now that the average surface temperature will rise as predicted by the aforementioned pessimistic scenarios, and that the seal levels will rise drastically.

How would tomorrow's Earth (in this scenario) compare to the Earth of the Cretaceous period ? Would it be in a similar state (besides temperature and sea levels), and perhaps share similar climates around the world, or would various factors I didn't mention (such as the ratio of oxygen in the air) make it very different ?

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  • $\begingroup$ Most optimistic scenarios predict a global rise of several degrees if no action is taken. The "no action" is the important point here. $\endgroup$ – Semidiurnal Simon Aug 7 at 17:27
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    $\begingroup$ Compare in what way? This really broad. $\endgroup$ – John Aug 7 at 19:00
  • $\begingroup$ @John Probably the most important criterion here (especially for people like me who have limited knowledge on climatology) would be the (in)habitability of various regions across the globe once climate change takes full effect. In particular, I am curious about how dinosaurs could live quite close to the poles (if I still refer to the Wikipedia page above, fossils were discovered in places which were only 15° from the poles during the Cretaceous). For instance, would places like Greenland get a climate much like what we currently have in Europe ? Sorry if it's a bit naive. $\endgroup$ – Jef Grailet Aug 7 at 23:15
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During the cretaceous the earth was on average 4 degrees warmer, but a 4 degree average results in nearly no change at the equator but a significantly higher rise at the poles, 8 to 15 degrees warmer. Antarctica was not covered in an icecap in the cretaceous period, although smaller ones may have formed periodically. Northern antarctica was largely covered in wet forest. Ecologically you would see wet temperate forest similar to those in australia and south america.

Note however warming was not the the only factor different positions of continents leads to a significantly different ocean circulation. Higher sea levels turn lowlands into seas changing rainfall patterns significantly. So the cretaceous is not a great predictor of the near future climate.

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