[mytailorisrich]

Iirc, the CO2 concentration now as been pumped up higher than it was then, which is in part what is worrying because temps might then potentially shoot even higher.

Bottom line: we need large scale carbon capture quickly because even if we reach net zero CO2 will take millenia to drop back to the level it was pre-industrial revolution.

Edit: I wouldn't focus on "pre-industrial levels" specifically, the point is that there is too much now so we most likely want concentration to drop as soon as possible.

[lehi]

The Keeling Curve is eye-opening for understanding our current versus (pre-)historical CO2 levels: https://tywkiwdbi.blogspot.com/2023/07/introducing-keeling-c...

[zosima]

One of the many misleading things done by climate scientists is to splice together data derived via different measurement methods.

The CO2 curve 800000 years back is an excellent example.

CO2 in air bubbles in ice will diffuse into the ice during the many millenia the ice have been stored under pressure. You can therefore expect the ice core CO2 to be lower than hypothetical atmospheric measurements at the same time.

The diffusion is expected to progress fastest at the start, and then more slowly.

Still the artifact is absolutely obvious as the CO2 concentration peaks are lower and lower the further back in time it goes.

Yet of course someone had to splice it all together and not even add error bars.

[japanuspus]

Not sure if you are trolling of really believe this to be true, but for anyone else assuming good faith: The diffusion aspect is (of course) well-modeled, see e.g. references under "past greenhouse gasses" at [0].

[0]: https://www.antarcticglaciers.org/glaciers-and-climate/ice-c...

[zosima]

This is a very interesting read:

https://www.cambridge.org/core/journals/journal-of-glaciolog...

They have found some meltwater layers with unexpectedly large quantities of CO2 > 750ppm.

But they also show that there is unexpected heavy diffusion around the meltwater layers. And they argue very compellingly, that the ice core CO2 records have been smoothed through natural diffusion.

Why is this information not given when showing this graph?

[MichaelZuo]

>750 ppm CO2 is incredible, if that's true it's no wonder that interglacial maximums could have been 5 degrees warmer than present day.

What's the causal explanation behind that much CO2 though? Super-volcano eruptions?

[zosima]

They explain in the paper. It's very likely an artifact.

But from the layers around it, it becomes clear that through the years these high CO2 bubbles leak CO2 to nearby layers.

And so CO2 highs are diminished in the ice core record and CO2 lows have been raised.

[zosima]

Where is it well-modelled? Noble gasses will diffuse differently from CO2. And on-top of diffusion of course CO2 will make hydrogen bonds with water in the ice.

It is well-understood that many ice cores give the same relative shape of peaks of various gasses through time.

Going from there to claiming knowing the absolue concentrations without very large error bars, is just not science.

[zosima]

Also, btw, this one is fun:

"Carbon dioxide measurements from older ice in Greenland is less reliable, as meltwater layers have elevated carbon dioxide (CO2 is highly soluble in water)."

[BurningFrog]

> Bottom line: we need large scale carbon capture quickly

The short term solution/bandaid is pumping SO2 into the stratosphere while we figure out carbon capture.

[XorNot]

I do wonder if some of the "massed solar sail" ideas for terraforming Mars' atmosphere would work here (in short: use cellphone processors to build and launch a couple hundred thousand solar-sail equipped satellites).

Because it would be expensive, but it would kill several birds with one stone: we (1) prove whether the concept would work on Mars, (2) develop the technology to do it, and (3) unlike SO2 in the atmosphere, "switching it off" or modifying the scale of the effect can be done almost instantly (you could remove the swarm by having it fall back to an Earth orbit).

[S201]

Is there anything left to really "figure out" about carbon capture? The tech works, it's just too expensive. Given a sufficient amount of cheap enough energy it could be scaled up as far as I understand.

As a layperson, it's just one more reason I so wish we'd invest in nuclear. Nuclear powered DAC plants might be the only way to scale it fast enough. Sure, it would still be expensive, but that's much cheaper than not massively reducing CO2 in the atmosphere.

[BurningFrog]

I think it's way, way too expensive now, and it will probably take a few decades to get it down to practically useful cost levels.

Which is why keeping temperature down with SO2 during that time makes sense.

[brutusborn]

Based on our record of environmental interventions; SO2 sounds suicidal. But it only lasts a few days in the atmosphere so maybe it has an in built off switch.

[BurningFrog]

Note that is for the stratosphere, not the atmosphere.

The mechanism is well known from volcanic eruptions, and it only lasts (from memory) 1-2 years in the stratosphere, so if something goes wrong, it can easily be tapered off.

[elzbardico]

Why do we need to get back to the levels pre-industrial revolution?

[angiosperm]

We have also pumped a very large amount of long-lived fluorine compounds into the air, that will last for centuries. They have from 2500x to 25000x times the "greenhouse gas warming potential", kg for kg. They are mostly refrigerants (CFCs, HFCs, and soon their successors) and transformer insulation gas (SF6). Volcanoes do emit some amount of fluorine compounds, too.

We also have a great deal of methane leakage, which is usually cited as 25-100x, and we may soon have a lot of hydrogen leakage, at >100x. Rocket launches are installing water vapor, another one, into the stratosphere like never before.

So even if we got CO2 down to a pre-industrial level, we would still have heat forcing from the fluorine- and other compounds.

Capturing CO2 is kind of pointless until we get emissions under control. I.e., a dollar spent preventing emissions buys much more than a dollar spent capturing. Solar panels and wind turbines directly displace mass emitters of CO2.

[mytailorisrich]

I don't know about all compounds but CFCs stay in atmosphere for about a century only and we've already banned them, and methane has a very short lifetime of about 12 years. So we 'only' need to control emissions of those to solve the problem.

On the other hand, as said, CO2 stays for centuries if not 1,000+ years so at this point net zero is only half the job though probably the hardest part.

[zdragnar]

Methane, at least, breaks down to CO2, no?

[angiosperm]

HFCs are not banned yet. They are responsible for 2500x CO2 forcing. Your car is leaking those right at this moment.

[specialist]

Yes and: I understand that we want to prevent the non-human emissions from becoming a positive feedback loop. Meaning that at some tipping point, the thawing tundra, burning forests, and acidic oceans will continue to get worse, even if/when human emissions completely stop.

[sleet_spotter]

Pre-industrial CO2 concentration is synonymous with the "natural concentration", at least in the recent past. We made a very large change that has thrown Earth's systems out of equilibrium. Returning to pre-industrial CO2 levels would undo that change and bring things back towards equilibrium.

[nonethewiser]

“Natural concentration” is not the right way to look at it because there are higher concentrations that predate the industrial revolution and humans. The all time high (that we know of) is from about 350,000 years ago. This was by all means natural and pre industrial revolution.

[adhesive_wombat]

"The only known natural concentration empirically compatible with long-term human civilisation".

"The planet did exist/will exist just fine without us" is a pretty worn truism. You might as well wryly note that water isn't natural because everything was hydrogen once.

[gottorf]

> empirically compatible with long-term human civilisation

Empirically observed, atmospheric CO2 went from ~320ppm to ~410ppm from 1970 to 2020[0], during which period the human population more than doubled from ~3.7B to ~7.8B and yet deaths caused by climate dropped threefold[1] (not 1/3 the rate; 1/3 in absolute number).

[0]: https://www.climate.gov/news-features/understanding-climate/...

[1]: https://library.wmo.int/doc_num.php?explnum_id=10989

[adhesive_wombat]

On the scale of human civilisation, 50 years is hardly "long term".

Polonium by that ultra-short-relative-term reckoning is not only harmless as it you still feel fine 10 minutes later, but actually healthsome as you rather feel refreshed by the delicious green tea you just drank in that 5-star hotel bar.

[colechristensen]

They are dynamical systems, there is no equilibrium. See also: climate charts for the last few ice age cycles.[1] In the bigger picture we want to modify Earth's climate and definitely do not want to end the current interglacial period, to be fair we've already done that, but returning to a "natural" pre-human climate cycle on the 10,000 year scale is not desirable.

1. https://energyeducation.ca/wiki/images/8/8f/Ice_ages2.gif

[pinkmuffinere]

Dynamical systems can have equilibrium points —- e.g. an inverted pendulum is stable when hanging straight down. If you deviate too far from an equilibrium point, the system may find another equilibrium that is less desirable for the user. I’m not an expert in climate change, but those things certainly happen for engines, robots, and other systems.

[thrashh]

Like the other reply said, there is no natural equilibrium.

We want to return to pre-industrial levels because we’re used to it and we liked it more then.

[tenpies]

I like to think of it as scrappy terraforming because we aren't even sure we could handle any of the naturally occurring variation.

Scrappy because, well the planet doesn't quite become uninhabitable and we're starting from the end-game. Science fiction also had me expecting some very cool terraforming infrastructure, not psy-ops to get the serfs to eat bugs.

[thrawa8387336]

Really

[mytailorisrich]

The point is that net zero is most likely not going to stop warming with 400+ppm CO2 in the atmosphere. CO2 concentration most likely has to drop but naturally it does so very slowly. Arguably at this point we already need cooling because 40+C every summer in half of Europe (for instance) is getting annoying...

[gottorf]

> at this point we already need cooling

A colossal volcanic eruption could do the trick, and those seem to happen rather unnervingly frequently.

[MichaelZuo]

Yeah it would be pretty silly for humanity to invest so much time and effort into lowering CO2 levels only for a Yellowstone or equivalent to erupt and send temperatures plummeting into a new ice age levels. When if humanity did nothing the eruption would only have taken us back to pre-industrial age temperatures.

[e_i_pi_2]

That is the point where we started adding greenhouse gases that lock in energy from the sun, we need to at least get back to those levels to start releasing some of the heat. Otherwise we're containing to add insulation to an oven that already overheating - you'd ideally want to take off all the insulation and the metal casing since you can't turn off the heat, but the casing isn't an option so we need to remove the insulation and hope it hasn't gotten too bad yet