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Comment by waiseristy | Hacker News Reader

Do we have historic evidence of runaway methane induced warming? It seems crazy that we are seeing these effects, but have nothing(?) in the geological records of these cataclysmic events

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Yes we do, but it's only a hypothesis. This was part of my PhD dissertation and one of my committee members is the world's expert on this topic. His name is Gerald (Jerry) Dickens. We believe this happened approximately 55 million years ago during an event called the Paleocene Eocene Thermal Maximum (PETM), an extreme global warming event. I've published a couple papers on this topic.

The way this works is, we run a computer model and try to come up with a scenario which matches the observations from that time period the best. And seems like the extreme warning that happened during the PETM was likely due to methane hydrate dissociation. I can link a few scientific papers if anyone is interested.

What were the temperatures and sea levels like at the time? Were there any major extinction events that coincided with it?

Edit : https://en.m.wikipedia.org/wiki/Paleocene–Eocene_Thermal_Max...

This is a good write-up. I'd still appreciate big picture commentary from domain experts, though.

In short, there was no major extinction (nothing like what happened during the end-Permian), some slow adopting benthic (deep ocean species) went extinct, however. The reason there was no major extinction was mostly due to the fact that the warming happened over a span of thousands of years. What we are doing to earth today is happening at a rate at least an order of magnitude faster than during the PETM (see the nature geoscience article I linked below), likely even faster. That wikipedia page has a good summary but here is Jerry's detailed scientific paper on this topic: https://www.diva-portal.org/smash/get/diva2:469826/FULLTEXT0...

This is my PhD adviser's paper. It is best to date estimate on the rate of carbon emissions during the PETM: https://www.soest.hawaii.edu/oceanography/faculty/zeebe_file...

Just realized I didn't answer all of your questions. The sea level was likely 50 to 100 meters higher than today: https://pdfs.semanticscholar.org/db73/f8e134ab32476aa08b3c05...

It was really warm, not sure on the exact number off the top of my head but at least 10-15 degrees C warmer in high latitudes than today. It was essentially an ice free world. And during the PETM event itself, the temperatures rose another 5 to 8 degrees C: https://dspace.library.uu.nl/bitstream/handle/1874/385777/Ex...

I'd be interested in a relevant paper, thanks.

Please check my reply to echelon.

I have seen models (and there was an article recently) how relatively small increase in temperature can reduce clod cover, reducing albedo and introducing another source of positive feedback and one that acts very fast.

Yes, there are likely many tipping points, some which we are aware of, and possibly some that we cannot even predict, which could cause a positive feedback. Once the tipping point is reached, the earth-system response might be highly non-linear, kind of scary to think about.

I'd be interested in the papers and if you could, summarize your contributions and/or your dissertation. Thanks!

Please check my reply to echelon. But here is one of my papers where we show that methane hydrate hypothesis seems to be the most plausible reason for the PETM warming: https://www.soest.hawaii.edu/oceanography/faculty/zeebe_file...

Seafloor sediments have been implicated in the https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis.

See for example http://burro.case.edu/Academics/USNA229/impactfromthedeep.pd...

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