[jbattle]

A) the lower bounds of climate change is now +2°C. The MWP was maybe +1°C.

B) (Possibly) I can't tell how long that change took to come into effect. One of the current concerns is how rapidly climate is changing.

C) Evidence points that the MWP only affected areas around the North Atlantic. Current climate change is having impact globally (though not equally so everywhere)

There were a ton of societal disruptions in the period of 950-1250. Vikings, Normal conquest of England, the Crusades. I'm not making an argument that any of those were caused by changing climate, but it definitely was a time of change with a heavy admixture of violence.

[soperj]

>One of the current concerns is how rapidly climate is changing.

Isn't there also concerns about methane in permafrost also amplifying the warming? Wouldn't that dispel the notion that it hasn't changed this rapidly before?

[paypalcust83]

Yes, the methane gun hypothesis. In modern times, there is an ever-growing risk of immense methane clathrates in the ESAS destabilizing and suddenly boiling off more than they already are. Methane has a GWP of ~1000x CO2 immediately, but it tends to dissipate within ~60 years with a half-life of roughly 7 years.

I would watch some videos on YouTube by Paul Beckwith and Natalia Shakhova about this topic. They are regular COP panel speakers. Natalia has been ringing scientific alarm-bells about methane hydrates since at least 2010, but not enough of the human family has listened yet.

https://www.youtube.com/user/PaulHBeckwith

https://www.youtube.com/results?search_query=natalia+shakhov...

[soperj]

So the rate of change isn't really an issue at all then?

[jbattle]

Yeah there are concerns about methane being released from melting permafrost. I can't find information about how old the permafrost is - but my understanding is tens of thousands of years old. I also can't tell if the methane itself is old, or if the methane just forms rapidly with all this newly thawed rotting vegetation.

https://www.vox.com/2017/9/6/16062174/permafrost-melting

There's evidence of times in the distant past where climate has changed very quickly, but all those predate history. There are some that even predate humanity. Here's an interesting one from ~12k years ago:

https://en.wikipedia.org/wiki/Younger_Dryas

[paypalcust83]

20 megatonnes/year is small potatoes compared to methane hydrates' 1-5 teratonnes storage that could go within a decade. There is at most 1.5 teratonnes of methane in arctic permafrost, but that will take much longer to release (50-100 years at a very conservative minimum) and it will degrade with a 7 year half-life.