Ancient CO2 spike collapsed forests for tens of thousands of years

[ParallelSelf90]

Researchers just published a study looking at what happened to forests during a massive CO2 spike about 56 million years ago called the Paleocene Eocene Thermal Maximum. That ancient event released roughly the same amount of carbon as humans could put out by the end of this century under a pessimistic scenario, and it pushed global temperatures up somewhere between 5 and 9 degrees Celsius for over 150000 years

The team used fossilized leaf cells from a site in Wyoming to reconstruct how thick the forest canopy was through the event, since sun leaves and shade leaves have different shapes depending on how much light they get. Canopy cover actually rose a bit at first, probably from the CO2 fertilization effect that gets brought up a lot in climate debates, but then it dropped 61 percent over the next few thousand years and stayed about a third lower for tens of thousands of years after that

One of the co authors made a pretty blunt point, saying that too much CO2 eventually raises temperatures past the point where plants can keep functioning no matter how much extra carbon they get to grow with. That basically sums up the whole fertilization versus heat stress argument in one sentence

What stood out to me is how long the recovery took. This was not a rough decade or even a rough century, it took tens of thousands of years before canopy cover properly came back, which is a sobering timescale if you think about what a modern equivalent might look like

Worth a read if you are into paleoclimate stuff, the leaf cell method they used sounds pretty clever for reconstructing something as fuzzy as forest canopy density from millions of years ago

Ancient rise in CO2 was catastrophic for forests: what that means for today's plantswww.nature.com

[Cheeky Kernel]

This is wild, I did not realize the PETM released a comparable amount of carbon to what we could put out by 2100 in a bad scenario. Puts the scale of it in perspective

[Undertaker]

The leaf cell shape thing is a neat trick honestly. Sun leaves being thicker and smaller than shade leaves is basic plant biology but using it to reconstruct ancient canopy density is a clever application

[Ryan65]

I feel like every one of these studies ends with the same conclusion, more CO2 helps a bit until it does not, then it gets ugly. At what point do we stop needing new studies to tell us that

[IvoryOttie]

Counterpoint though, 150000 years is an insanely long window for temperatures to stay elevated. Modern warming is happening way faster which could make the outcome worse or could mean ecosystems adapt differently, nobody really knows

[Penguin79]

Not sure I buy that ancient analogs map cleanly onto modern forests since species composition, soil chemistry and everything else is totally different now. Interesting as a data point but I would not draw hard conclusions from it

[Matthew51]

Appreciate that this is published in Science and not just some press release. A lot of climate coverage skips the actual methodology, this article at least explained how they measured canopy cover

[RicFlair_What?]

Does anyone know if there is a similar leaf fossil record for other parts of the world during the PETM or is Wyoming basically the best preserved site we have

[TheRock96]

Ferns replacing broad leafed trees in the mid latitudes is such a specific and slightly eerie detail, imagine watching that kind of shift happen in real time

[Quarry57]

The tens of thousands of years recovery time is the part that gets me. We talk about ecosystem recovery like it happens in a human lifetime but geologically that is barely a blink and it still took forever

[Layla_61]

Genuine question, does the fertilization boost they saw at the start actually offset carbon loss elsewhere or is it basically cosmetic and temporary