Extreme El Niño weather switched off South American's carbon sink | Hacker News Reader

Extreme El Niño weather switched off South American's carbon sink

leeds.ac.uk

102 pointsgeox37 comments

Full article, open access, is at Nature Climate Change:

Sensitivity of South American tropical forests to an extreme climate anomaly (04 Sep 2023)

https://www.nature.com/articles/s41558-023-01776-4

First time I've seen the word, "necromass" though:

> "Among the key processes governing the carbon balance of tropical ecosystems are the rates of tree growth, which takes carbon into the biomass pool, and tree mortality, which transfers it to necromass. In turn, both growth and mortality are likely to depend closely on plant available water, temperature and their fluctuations."

Curiously old-growth forests seem to slowly draw down CO2 even at mature stage[1], it may end up sequestered in soil (see also peat bogs, permafrost carbon, etc.). This leads some credence to the notion that recent human activity has 'refertilized' the environment with CO2 - although since we're apparently back to CO2 levels last seen in the Pliocene, 3-5 mya, now would probably be a good time to stop. Re-creating widespread ocean anoxia is not a good idea, even if that's what allowed most oil & gas deposits to form some hundred million years ago.

[1] Old-growth forests as carbon sinks (2008). https://www.nature.com/articles/nature07276

The actual paper, which is a PHd thesis, is titled "Impact of the 2015-2015 El nino on Tropical Forests." It suggests that it is possible under _sustained_ hot and dry conditions, not single year weather events, for the carbon sink of _some_ forests to become reversed. This hyperbolic article even has to end with the same conclusion, that if we manage to keep the forests standing, the carbon sink will NOT become "switched off."

It's odd to see an institution engage in such absurd sensationalism on one of it's own researchers thesis. The carbon sink doesn't have a "switch" that "El nino" somehow magically presses.

You are misrepresenting the science here. This wasn't "just a PhD thesis" in particular.

Also, your take of this to be "sensationalism" is very odd. The danger of imminent tipping points turning "climate change" into "climate catastrophe" is absolutely real.

> The researchers today report their findings in the journal Nature Climate Change. The study united the RAINFOR and PPBio research networks, with dozens of short-term grants enabling more than 100 scientists to measure forests for decades across 123 experimental plots. The plots span Amazon and Atlantic forests as well as drier forests in tropical South America.

> These direct, tree-by-tree records showed that most forests had acted as a carbon sink for most of the last 30 years, with tree growth exceeding mortality. When the 2015–2016 El Niño hit, the sink shut down. This was because tree death increased with the heat and drought.

Now wait till the forests burn and instead of being a carbon sink, they become a carbon contributor.

Hi Canada!

I think our peatlands are of considerably greater concern.

In Ireland we're burning ours, like a bunch of idiots.

The situation with Canadian forests is much worse. The Amazon accounts for 20% of the global carbon sink but the meters-thick layer of peat below Canadian forests is a third of all carbon stored (along with the peatland in Russia, which is also burning).

There’s enough carbon stored in that peat to double or triple the CO2 ppm which would be absolutely catastrophic to the planet.

Those trees are made of carbon that was already in the atmosphere, and they will release it back into it whenever they die in the next couple centuries anyway. Trees are basically irrelevant as carbon capture, unless they're cultivated to maturity and then buried underground.

They tie up carbon for 100+ years, they're hardly irrelevant

Depends on if you are a climatologist or a geologist.

They buy a little bit of time. That's it.

Nonsense, a region that is forested has a proportion of carbon locked up in biomass indefinitely. If that region is deforested and no longer has any carbon locked up in biomass that is unambiguously a net source of carbon.

It's not locked up, it's continuously flowing in and out of that ecosystem. It's only locked up when it gets buried and can't return back to the atmosphere (except through technology). There's any number of reasons why a forest could get disrupted and die out besides intentional deforestation.

Admittedly I haven't checked for sources, but I'm willing to bet that it's mostly man made these days, either direct deforestation or climate change.

I hate to break it to you but we need all the time we can get. Also a rotting tree doesn't completely turn into gas, some of the carbon (I think 30%?) goes into the soil.

If you’re in a sinking boat it is the amount of water inside the boat that you worry about, rather than the amount of water in which the boat is floating.

If you're in a sinking boat you should worry about how fast water is coming in, not about how much water is inside. Would you rather be carrying 10 tons of water without leaking, or 1 ton of water and taking in half a ton per minute?

That's not how it works, the time the carbon got stored has an effet on the climate, the same way that 1 euro tomorrow isn't the same as one euro today.

> trees are basically irrelevant as a carbon sink.

Some quick googling shows me that all flora on earth hold about 1000 gigatons of carbon, whereas we are releasing about 40 gigatons per year. Doesn’t seem irrelevant.

Meaning we would need to plant the entire current flora every 25 years just to break even. Sounds pretty close to irrelevant.

In fairly sure flora also plants itself if we leave it alone..

I'm fairly sure the total biomass of flora on Earth is fairly consistent across human time scales. It's not going to double in 25 years and then continue increasing at that same rate.

Do you have evidence for that? I in turn would assume that there's considerably less flora since the industrial revolution. If you ever kept a garden you know how fast weeds colonise bare soil.

However, intact tropical South American forests overall were no more sensitive to the extreme 2015–2016 El Niño than to previous less intense events, remaining a key defence against climate change as long as they are protected.

https://www.nature.com/articles/s41558-023-01776-4

They're simply reporting that conditions of high temperature and drought reduce photosynthetic fixation rates more than they do total respiration rates (and fire losses). What's significant about the research is that they actually quantify these rates using a network of hundreds of carefully monitored forest plots across the region, it's not based on a computer model.

Overall they report that the tropical forest across this region became carbon-neutral, i.e. no more carbon was taken up than was released. Looks like careful rigorous science to me.

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