Earlier this week a paper I co-authored – in which we use geophysical models of methane hydrates to work out how quickly they may have dissociated and escaped into the ocean during the Palaeocene Eocene Thermal Maximum (PETM) ~56 million years ago – was published over at Geophysical Research Letters and featured as a Research Spotlight by AGU’s Eos.
The latter does a good job summarising it for those without access to the article (though if you’re on Researchgate you can find an Open Access version), but to summarise in my own words here our results suggest that while hydrates could rapidly dissociate during the rapid warming of PETM, it’s difficult to get that methane out as quickly as it gets trapped in sediment pores on the way up (where it can also get eaten by microbes). For lots of methane to make it to the ocean there either needs to have been a lot more hydrate deposits in the late Palaeocene than we thought (which may be unlikely in the warmer oceans of back then), or cracks and fissures may have played a key role in allowing the methane to seep out. Without either of these it becomes quite challenging to explain the big carbon cycle disruption seen in the palaeorecord at the PETM using methane hydrates as the primary driver alone.
This is not to say that we’re safe from methane hydrates now though*, as global warming today is proceeding far faster than at the PETM. During the PETM temperatures rose roughly 5 degrees celsius over 1000 to 10,000 years, whereas today we’ve already pushed up temperatures 1 degree over the last century and could hit 5 degrees in total in another century-plus in a no-holds-barred scenario. More rapid warming could induce a different dissociation to release ratio this time round, and if pressure-induced cracks did play a role in letting methane escape during the PETM then this could be important in projecting how methane is released from hydrates in the coming centuries. Of course, these are good places for further research – just how much escaped in the past, and how might very rapid warming affect this?
*I noticed our research was picked up by Breitbart.com – not known for accurate reporting on climate issues – presumably because it might look like we’re weakening a prehistorical example of carbon-induced climate change. Of course, there’s still a massive carbon release event recorded simultaneously with warming during the PETM which our work does nothing to weaken, and as explained above it’s not an ideal comparison for the future anyway due to differing warming rates.