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Comment by alex_duf | Hacker News Reader

>whether the growth of renewables outpaces the depletion of our carbon budget

I'm not sure I understand. There's no carbon budget, any carbon that we emit is carbon we'll have to re-capture somehow and the longer it stays in the atmosphere the longer it will have a heating effect.

I think renewable have accelerated to the point of matching the electricity growth worldwide: https://ourworldindata.org/grapher/electricity-production-by...

We've also passed the peak of CO2 per capita, but since the population is still growing we are still increasing carbon emitions worldwide. It's going to be a while before we stop emitting anything, and then longer before we start re-absorbing it...

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Whenever I hear "carbon budget", I usually understand it as "how much CO2 we can still emit (net of sinks) before the warming passes a certain threshold (for example, some level of the Paris agreement.)

Is that a misunderstanding on my side ?

I highly doubt that we will have global negative emissions (CO2 capturing) within the next decades-- maybe by the end of the century.

Even very rich nations have a handful of prototype plants for CO2 capture right now at best, and the budget for things like this is the first thing that gets slashed by Doge et al.

If we were on track for lots of CO2 capture by 2050, we would see the beginnings already (massive investments, quickly scaling numbers of capture sites, rapid tech iteration).

Fully agree with the rest of your point though. I consider CO2 emissions as basically "raising the difficulty level" for current and future humans (in a very unethical way, disproportionately affecting poor/arid/coastal nations).

I'm also highly confident that human extinction from climate change is completely off the table (and I think a lot of people delude themselves into believing that scenario for no reason).

If electricity is sufficiently cheap it can be cheaper to capture carbon from the atmosphere for chemical industry than to use oil or coal there.

Do you have any source for this extraordinary claim? It's practically a claim of perpetual motion.

Carbon dioxide a tiny fraction of the atmosphere, even in concentrations which are immediately harmful to human life.

At the moment it's 400 parts per million. So in order to extract 1kg of Carbon Dioxide from the atmosphere you have to pump 2500kg of air through the system. This alone makes it unlikely we can do this profitability.

You then need to extract the carbon dioxide using some technique which will probably involve cooling or pressuring that volume of air. Before finally transforming carbon dioxide, a very stable chemical compound, into a reagent which is actually useful (probably carbon monoxide).

Difficult engineering problem but working from first principles suggests that the energy requirememts are not insurmountable. The roundtrip efficiency is worse than batteries but much better than photosynthesis.

Terraform Industries (and others, like Synhelion) has a plausible if slightly optimistic target to be price competitive with fossil fuels for methane in the early 2030s.

Some places with very cheap to extract hydrocarbons like Saudi Arabia may be able to compete for a very long time, but there are many futures where most of humanity's hydrocarbon consumption (including the ones used for the chemical industry, plastics, etc) derives from atmospheric carbon.

And this can happen fast, the world (mostly China) has developed a truly massive manufacturing capacity for PV.

Terraform Industries (and others); I'd seriously consider taking a long bet that these companies turn out to be better at converting investor capital into employee salaries, for a finite period of time, than they are at converting atmospheric CO2 into natural gas.

If such a technology was possible then it would be far better to start with carbon capture from existing emitters. The concentration of CO2 being easily 3 orders of magnitude higher.

For hydrocarbon synthesis, hydrogen production from electrolysis dominates the energy usage, along with driving the Sabatier process. DAC might be like 5-10%.

Higher CO2 concentration is better but certainly not needed, it doesn't make or break the economics.

I'm not going to argue over the numbers but any business which ignores such an obvious upside / upside scenario is not really serious about achieving economic criticality. It would allow a power plant, iron ore plant, cement producer, what have you, to make claims about their environmental credentials while simultaneously improving the efficiency of the process.

They said "If electricity is sufficiently cheap", which is less a claim and more a tautology.

Will it be that cheap? I think so, given that trees and grass etc. exist and get their carbon from the air.

Even with free electricity, the capital (and maintenance, consumables etc) costs of the process could easily be too high.

I suppose that in principle that is indeed possible; in practice, trees exist and self-seed, so the limit is our own ignorance.

We are also limited the incentives to that make us cut tree for money, and not develop technologies if they are not profitable within a short time-window. We have the technology to plant more trees right now, but we aren't.

People plant loads of trees for lumber, but you're right, it's an economics question in the end.

This actually means I'm also worried about something currently impossible: that when we do develop the tech sufficiently to be useful, if it's cheap enough to be profitable, nothing would seem to stop extraction. So CO2 goes down to, what, 300ppm? Pre-industrial? Ice age? Same coin, other side. We want to flip a coin and have it land on the edge.

A single world government could organise to fix this either way, but as all leadership roles come with the risk of the leader being fundamentally bad, this isn't something I'd advocate for either.

> that when we do develop the tech sufficiently to be useful, if it's cheap enough to be profitable, nothing would seem to stop extraction. So CO2 goes down to, what, 300ppm?

This is an extremely improbable scenario, for several reasons:

1) If you actually use the extracted CO2, then it gets re-emitted on use, and the atmospheric concentration is virtually unaffected.

2) Concentration difference alone makes it very unlikely that we'll ever extract CO2 as cheaply as O2 from ambient air (or carbon from a mine), and CO2 is not really an appealing ressource compared to its components, either (so demand would presumable be pretty low for centuries, even if the price comes down a lot).

> 1) If you actually use the extracted CO2, then it gets re-emitted on use, and the atmospheric concentration is virtually unaffected.

Depends what you use it for, e.g. synthetic diamond windows won't re-emit unless they catch fire.

> 2) Concentration difference alone makes it very unlikely that we'll ever extract CO2 as cheaply as O2 from ambient air (or carbon from a mine), and CO2 is not really an appealing ressource compared to its components, either (so demand would presumable be pretty low for centuries, even if the price comes down a lot).

Underestimating how big an industry would get is the mistake Svante Arrhenius initially made, thinking it would take millennia to emit enough CO2 to cause noticeable global warming.

And remember, with this concern I'm inherently presuming tech (mainly energy) that makes it sufficiently cheap that business and/or governments are willing and able to remove in the order of at least one teratonne of the stuff (but hopefully not two or more teratonnes) — because less than that, it's not solving global warming.

You could make the same argument about AGI. Just because nature does it doesn't mean it's easy for us to replicate in an industrial setting.

Sure, but you said "It's practically a claim of perpetual motion." which is overstating the challenge to a much greater degree than this understates it.

Consider a chemical synthesis that needs carbon. Right now it uses oil. But is has to be extracted and transported. With carbon capture from the air that no longer required. And maintaining the extra facility at the chemical factory can be cheaper than maintaining the extraction and supply chain for oil or coal.

Yes. But it still has to compete with all the various types of biomass, for example.

It may never be “worth” it in economic sense, but it offers a way to separate the time of “energy is used” and “energy is available”. Assuming sufficient captureable volume you could capture the emissions of a fossil power plant during the ~two weeks per year where weather is sufficiently bad. And then take the other 50 weeks to capture that carbon again. It can be completely inefficient (like sub 5% round trip efficiency) if a) we pay for it via a capacity market and b) have sufficient excess (clean) energy to run it

The idea that we'll have huge excesses of clean energy seems like wishful thinking. We may have issues with excess energy at certain times of day for sure. But intermittent excesses like that are difficult to make use of economically because of capital costs and low utilisation. A general excess would be countered by falling energy prices to the point that it's difficult to make a business case for new installations.

I don't see a future where technologies which are massively inefficient reach their break even cost before other energy intensive activities or more efficient grid scale storage soak up the excess.

Of course it seems like wishful thinking! Because that’s the historic norm. Energy was (in some way) always the limiting factor. And every time energy access got meaningfully cheaper society massively reorganised around it.

And yes “energy” in general won’t be free. We still need to build the generation and distribution systems. But we reached a point where just dumping solar on all _new_ roofs rounds to essentially free (the costs are the labor and the access to qualified personnel). The exact same is currently happening to batteries. Any transformer project will be able to just integrate 4-12 hours of batteries without getting meaningfully more expensive. The same for every domestic or industry service upgrade

We are not there yet. But give it another 5 years and we will. And then we are only talking about financing what little distribution system we will need (basically you only need average-sized cables not peak-sized ones) and a capacity market for backup power systems (also only for average residual demand). And those we simply cannot (efficiently) finance by a per-kWh-used charge

    > If electricity is sufficiently cheap

It never will be.

If you actually use captured carbon for something productive like synthetic fuel (where CO2 gets re-emitted) you are kinda ruining the point though.

Thats what makes this even less attractive-- those plants are expensive to build and operate and you can't even really use the product in the most obvious ways.

This about using carbon for chemical industry.

"Even very rich nations have a handful of prototype plants for CO2 capture right now at best, and the budget for things like this is the first thing that gets slashed by Doge et al."

Might want to take a look at China, or at least what IEA writes about CCUS and the like there.

https://www.chinadaily.com.cn/a/202505/09/WS681d52e5a310a04a...

The problem with carbon capture is volume. There is about 0.04% CO2 in air. So in order to remove a ton of CO2, you would need to process thousands of tons of air, depending on the efficiency of the extraction process.

It's just kind of infeasible to pull the entire atmosphere through these plants. The largest one we have is called mammoth, claimed to remove 36000 tons of CO2 per year, meanwhile our emissions are measured in billions of tons per year. Like over 30 billion.

We would need about 30 mammoths to get to a million tons per year, and 30,000 mammoths to get to a billion. Then multiply by another 30 and in total we would need almost a million mommoth plants just to undo what we are doing right now at the same rate. Carbon capture is like trying to empty the ocean with a bucket.

How are you so confident that extinction is off the table? I've stopped following this stuff because it's depressing but last time I checked we were in dire straits and I haven't heard any good news on this front. I'm just seeing ice caps disappearing, ocean currents changing, weather changing, pretty much everything that's been predicted is now happening and it's not going to slow down any time soon.

> How are you so confident that extinction is off the table?

Because even the worst-case scenarios (=> think RCP8.5) are just not enough to get rid of us.

I can totally see populous breadbasket states turning into unliveable deserts, billions of deaths from famines and heatwaves, iconic coastal cities being lost to the sea and a giant loss of biodiversity-- but I simply don't see this eradicating our species.

Humans are too adaptable, and warming is invariably gonna leave too many survivable holdout regions.

I think that an all-out global nuclear war would be much more threatening to humanity, and even that I'm very confident we would survive as species.

Yeah so this is mostly just a difference of definition. When I say extinction I mean what you describe, essentially a total collapse of modern society. I don't care whether/how long a few people survive somewhere, your scenario is apocalyptic enough for me to label it an apocalypse.

I also think this process is likely to trigger a new world war. When nations start collapsing there will be two possible outcomes - other nations take them in or they go to war. They won't just sit down and die. And everyone else won't be able to handle the number of refugees even if they want to.

But what's the probability of those direct climate effects happening without an all out nuclear war on the side, as a second order effect of the climate change? Humans are prone to fall for whatever radical ideology crosses their path when the future looks bleak.

I don't believe in world-war as byproduct of climate change yet.

I think capability to wage war internationally will probably decrease thanks to climate change; it is much easier for a state to prevent the peasants from starving than to feed/equip/fuel an army.

I also don't really see the incentives working: Countries like Bangladesh that are gonna suffer disproportionally are mostly not in a position to wage war offensively, and famines/heatwaves are not gonna make it any easier.

My admittedly cynical outlook is that it will just be business as usual: More affected/poor nations struggling, while wealthier western states moan about refugees, use their wealth as buffer and proceed to not care about people dying elsewhere.

I mostly agree with your assessment, except that "moaning about refugees" and resulting action is going to get a whole lot worse as the numbers increase.

We're already seeing how countries like the UK and US can be manipulated to respond to these situations, even when their effects are mostly imaginary and even net positive. Imagine what will start happening if the bogeyman of migration becomes a real problem.

"Use wealth as a buffer" works in the current scenario to some extent - although the US seems to have a lot of trouble with it. But what will scaling that look like? Trumpian concentration camps throughout the country, ICE budget approaching that of the US military, national curfews, martial law, suspension of habeas corpus...? We've already seen hints of all these things.

Things could get very bad. But I agree, not extinction-level, yet. Give us time though!

>I highly doubt that we will have global negative emissions (CO2 capturing) within the next decades

Just to clarify what I wrote, I also highly doubt we'll get it at scale in the near future. We desperately need it though, as well as any other measure that will bend the trends in the right direction.

This may not be the right place for this, but I'm honestly getting very anxious about our climate. Some of the data such as the temperature anomaly is showing an exponential trend. See the scariest graph I've ever seen here: https://www.nytimes.com/2025/06/26/climate/climate-heat-inte...

Shrinking? China is growing their coal capacity (1). What people mistake is China is not "for renewables". They are for maximizing absolute output. That means they are "for everything"

(1) https://www.reuters.com/business/energy/china-has-more-than-...

I didn't mention any shrinking. I just said we'd passed the CO2 per capita peak.

https://ourworldindata.org/grapher/co-emissions-per-capita?c...

This means for any human being we are emitting less carbon than we use to. It's not a big win but I'll take any good trend at the moment.

China ist still adding coal plants but their capacity factor is falling.

In fact Chinas emissions have probably already peaked.

https://www.economist.com/china/2025/05/29/chinas-carbon-emi...

https://www.carbonbrief.org/analysis-clean-energy-just-put-c...

https://www.sustainabilitybynumbers.com/p/china-coal-plants

My apologies. By available carbon budget, I meant the carbon we can burn before we exceed 1.5 degrees, or 2 degrees etc.

I think 1.5°C is already basically impossible; scenarios between 2°C and 4°C by 2100 over pre-industrial levels seem achievable-- that would be a total remaining CO2 budget of ~3 Tera-tons of CO2 within 2100.

That is an average of 4 tons of CO2/person/year for 10 billion people. Americans are at 3x that right now, Europeans/Chinese 2x, and a few wealthy nations are already there (France, Switzerland, Israel). Poorer countries like India are significantly under that value (for now!).

Doubling that CO2 budget to 6000 Gt would make things significantly worse (5° expected temperature increase or more).

1.5 degrees was last year.

https://climate-adapt.eea.europa.eu/en/news-archive/copernic...

Oh, we're definitely going to need direct air capture, which consumes massive amounts of energy. Fortunately, it's only massive compared to things like global shipping, not compared to the sun that hits the Earth.

I see, thanks for clarifying I got confused there.

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