Thread by @anlomedad

Studying the 1.5˚climate plan for Germany by NGO @_GermanZero written by experts in all relevant fields, incl. hard-sci (Mojib Latif) assets.website-files.com/5e663c02af4002… Stumbling over 20% rest emissions, and general compensation logic.

I'll assume, global 20% rest emissions = 8Gt/year

Here's the German version of GermanZero's climate plan assets.website-files.com/5e663c02af4002…
I might do another thread on the plan itself. But now, I'm interested in the other thing: the rest emissions from hard to decarbonize sectors and how natural compensation mechanics work for *net* zero.

I have issues getting the logic of continuously sequestering these 8Gt/a CO2 emissions. I myself calculated with a similar number before but never bothered to really think it through.

I know: flux into terrestrial carbon sinks under current 38Gt/a CO2 is different than for 8Gt.

Questions to answer for further assumptions:

With 8Gt human CO2 emissions by 2040 (planned global netzero year), how much do natural carbon sinks still absorb per year? Consideration has to include 20% inevitable loss of carbon sink by 2040, as per recent paper on real-life data

Is the sequestering performance of 8Gt/a meant in addition to negative emission tech for reducing CO2 concentration in the atmosphere, or can both be combined?
In other words: can we burn x% of 8Gt/a worth of trees, capture and store or use the CO2, ie BECCS - and then regrow y%?

Answers. (I hope...)

I know: flux into terrestrial carbon sinks under current 38Gt/a CO2 is different than for 8Gt. Today, land absorbs 30% of emissions. By how much does that % change under 8Gt? And feedbacks from rising temperature also impact the carbon sink. But by how much?

A while back, I did a thread on this model study paper exploring efficiency of negative emission tech (with focus on sea level rise). It also explains in general what happens to the carbon sinks in that process.
I won't repeat the model setups here, just general info re CO2 flux

Zickfeld et al iopscience.iop.org/article/10.108… let their various models remove up to 6GtC per year. Our 8Gt CO2 rest emissions are in the lower band of removal, ~ 2.2GtC, the equivalent of their "VCE 550". VCE550 are the 3 pictures on the right in this tweet:

https://twitter.com/anlomedad/status/1312775825150930949

Just a mo! Our rest emissions are 8Gt CO2 or 2.2GtC per year. 8Gt to be "neutral"! We're not talking of removal from the carbon cycle, yet!

Hence, what we can roughly expect to happen under net-0 and at 1.5˚ (!!!) is shown in f) North emits, South takes up. Just like today...🙃

CO2 flux at net-0👉boreal emits, South takes up. Incl. oceans we're roughly balanced in outgassing and uptake, maybe more outgassing than uptake, to be on the safe side in our assumptions. Say 1Gt? But that's the model theory.
And only pertains to near 1.5˚!!
In practice, tho..

In practice, and at near 1.5˚warming -not valid for 2˚!, we can expect things to happen to the land carbon sink which Zickfeld and colleagues didn't observe in their purely theoretical models.
1)Already mentioned: Inevitable 20% loss in terrestrial carbon sink. But!

But! The 20% loss is only from the CO2 balance in respiration vs photosynthesis under rising heat stress, not from🔥🐞💧

And the 20% are the total loss since 1900.
From today to 2040, we'll only have an additional ~ 5% loss increase IF we stay near 1.5˚ advances.sciencemag.org/content/7/3/ea…

2) Plants already suffer and it will increase by each tenth of degree. They'll burn, dry, die from more pests.... But how much loss in carbon sinks does that amount to? For net zero we need to add that to the theoretically assumed outgassing of +1Gt/a and observe the 5% loss, too

What's the logic here? Assuming a world on 8Gt, attempting to compensate those 8Gt. With:
*a biosphere on reduced general capacity by 2040 compared to today's plants alive
*also outgassing of 1Gt/a from sinks just bc theoretically, that's the reaction to a warmer climate

I can see we need to compensate parts of outgassed 1Gt. But do we need to calculate with loss in carbon sinks from heat/drought/pests, too - and compensate them, as well?

What they were doing so far was taking up 30% 11Gt of current emissions. But 2040 we'll only emit 8Gt. So?

Why wd I have to observe the 🔥losses at all?
For net zero from 2040, compensation need is 8 + 1Gt.
I COULD assume, under 1.5˚ (!! totally different under 2˚!!), oceans and land still manage to take up their 50%, minus 1Gt. They might still manage to take up net 3Gt annually...

That'd be 3Gt versus ~ 19Gt today. 3Gt of which land takes up 60% and oceans 40%. I can't imagine land carbon sink to be reduced so much that it can't manage 60% of 3Gt. Surely, it will still be able to do that, despite the losses from fires, pests, water and added heat stress.

(An altogether different thought is how food production is affected.)
But yeah. In practice, I do not have to juggle with the tree losses when compensating the residual emissions from 2040 onwards.

Altho... losing them also means more CO2 in the process. CO2 from fire and death.

Gotta go now. But gotta think that through. Man.... I really lack cognitive ability here. Can't get my head around and all the way through the changed carbon cycle and its amounts by 2040.

So. I'll come back later. Maybe you get my brain blockade? Do you have some input?

Got it. I'd not have to juggle with losses UNTIL 2040, at all. Phew.

In 2040, I'll have a certain capacity status in the biosphere. To which I'll have to add capacity for ALL of my residual 8+1 Gt CO2.
Just a moment. For all, or for parts of 8+1? Or rather: more than 8+1? 🧐😳

More than 8+1? Because the losses until 2040 have occurred due to climate feedback processes🔥🐞🌡️and those will continue after 2040 and incur further losses/a. Yup.

For net zero, the annual losses in land carbon sink (and ocean if any) must be compensated from 2040, as well.

The question whether I should have to compensate less than 8+1 came from the notion that it'd be okay to let oceans still foot parts of the bill.
Oceans do that, anyway. It's just how it works. But I can't deduct ocean takeup from my biocapacity for 8+1+an annual increase for 🔥

This is my compensation formula for 2040ff so far:
8+1+an annual increase for annual biocapacity losses due to🔥🐞🌡️💧

But.
All the biocapacity losses also incur an additional CO2 emission. Fire is obvious. But also decomposing after death from pests or drought causes CO2.

So the extended formula for 2040ff is now:
8+1+an annual increase for annual biocapacity losses due to🔥🐞🌡️💧+the added CO2 from these losses.

But does that mean 100% of these losses plus CO2 from the losses must be annually compensated?

Like for example #AUSfires emitted 800Mt in early 2020. If that happens in 2041, it'll add to our compensation burden in 2042.
But 800Mt?
How does that compute?
*The forest grew back some in a year, ie took up some of its fire emission.
*OTOH, AUS forest capacity was reduced.

Nah, man, this gets complicated!...
I gotta go for now, anyway. My head explodes. It's what happens when subsurface climate anxiety steals sleep and lets you get up at 2:30am twice a week: you find yourself in climate-caused cognitive capacity conundrums. 😂