Have CO2 emissions peaked?

I noticed, as has Stoat, that Ken Caldeira and Ted Nordhaus have a bet about whether or not we’ve reached peak CO2 emissions. Specifically, the bet is

Between 2021 and the end of 2030, annual fossil fuel emissions (excluding carbonation) will not exceed annual fossil fuel emissions (excluding carbonation) from 2019.

Carbonation is essentially emissions from cement production.

As with many others, I’m hoping that Ted Nordhaus wins, but expecting that Ken Caldeira will do so. In truth, though, that’s a bit simple. Even if Ted Nordaus were to win, what would emissions having peaked actually imply?

Consider a simplified form of the Kaya Identity:

CO_2 = GDP \times \dfrac{Energy}{GDP} \times \dfrac{CO_2}{Energy}

CO2 emissions essentially depend on Gross Domestic Product (GDP), energy intensity (energy per GDP) and carbon intensity (CO2 per energy).

So, if emissions this decade do not exceed those from 2019, why would that be? Would it be because GDP growth had stalled? Would it because of improvements in energy efficiency? Would it be because we’d reduced emissions through using more alternative energy sources? Would it be because we’d developed, and deployed, carbon capture and storage technologies? A bit of everything?

Also, what would it imply about the developed and developing worlds? Will the developed world have accelerated their emissions reduction so that the developing world can have a more gradual transition? If it is partly due to slower, or stalled, GDP growth, would that imply that some have benefitted far less than they might otherwise have done?

I don’t know the answers to any of these questions, but I do sometimes wonder if we don’t always consider the potential implications of some of the scenarios we might be hoping for. I’ll leave it there, but if anyone has any answers to these questions, feel free to post them in the comments.

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92 Responses to Have CO2 emissions peaked?

  1. I’ve just found this article, by James Temple, which somewhat illustrates what I’m trying to get at:

    Some argue that the radical changes in behavior and practices that went into effect as the coronavirus spread around the planet are a promising sign for our collective ability to address climate change. This is, frankly, nonsense.

    Huge portions of the population stopped driving to work; going to bars, restaurants, and theaters; and flying around the globe. Economic growth plummeted. Hundreds of millions of people lost their jobs. Hundreds of thousands of businesses have closed for good. People are going hungry. And the world is becoming much poorer.

    None of this is a viable or acceptable way of slowing climate change.

  2. CO2 emissions so far have on a global scale (the only scale that matters for climate change) only been reduced during times of crisis and never as an effort of climate conferences or other reasons. So I’m not very optimistic. As soon as the corna virus crises is over it will be back to Business as Usual. Co2-emissions will be back to previous pre-crisis level.

  3. In what universe does it make sense to argue or bet on whether CO2 emissions have peaked minus the emissions related to carbonation? That seems like an exclusion that is large enough to drive a cement truck through.

    I think it only makes sense to attend to the atmospheric level of CO2 and CO2e. That means we must be concerned with all sources of CO2 and CO2e emissions to the atmosphere and with the function of the planetary carbon cycle in response to changed and changing conditions.

    The James Temple article makes sense to me and seems on point. The Caldeira/Nordhaus bet looks like a circus sideshow event to me.

    Let’s say that Nordhaus wins the bet, even that Nordhaus might win easily, but carbonation and changes in the carbon cycle cause atmospheric levels of CO2 to continue to rise to a level that creates global temp rise of 3 degrees or more. In that scenario, who cares that Nordhaus has won this bet? Other than that, Ms. Lincoln, how was the play?


  4. Chubbs says:

    It is an interesting question. Worth looking at each fuel separately. Coal stopped increasing around 2010, mainly due to China, and could start heading down after a plateau as economics falter. Oil has been increasing slowly; but the pandemic hurt demand, some of which may never come back, and competition from electric is increasing. The jury is still out on whether oil peaked in 2019, but in any case oil is peaking, and any growth beyond 2019 is likely to be modest. Gas has been increasing and gas demand should resume its increase after the pandemic.

    Putting it all together, we are in better shape than we were 10 years ago, in a broad plateau instead of a steady increase. The fact that peak CO2 is discussed is positive. The bad news is we need to do better. A slow decrease in CO2 emissions still leaves us with steadily increasing CO2 concentrations and decreasing aerosols if coal—>gas. If methane/N2O continue to increase, forcing will continue to increase unabated.

  5. This was happening even before the pandemic started, which just moved it along at a quicker pace

  6. The Department of Energy’s Energy Information Administration estimates energy consumption growth of 3% through 2050 (https://www.eia.gov/outlooks/ieo/pdf/ieo2020.pdf). They forecast increased consumption of all fuels–renewable growing the most, but even coal sees modest increase due to development in Africa and South East Asia.

    Cement causes 6% of CO2 outgassing and it is perhaps wise to exclude it from emission calculations for a bet. First, it is very hard to predict future trends in construction–they respond to changing economic conditions much faster than other causes of emissions. Does anyone really think they have a good idea on short term trends in office construction in the new age of Zoom?

    Second and more important, technology innovation looks to dramatically impact the CO2 used in the creation of cement. It could be really good news and could happen fairly quickly.

    Look for peak emissions around (roughly) 2050.

  7. Temple’s argument fails to consider that business travel usually isn’t fun, and business commuting is almost never fun. Those reductions are positively beneficial to humanity and we should hope they continue as much as possible.

    I’ll also add that the millions of people who’ve learned to do Zoom videos with relatives may continue doing that. While it doesn’t substitute for all in-person visits, and I expect there will be a temporary surge of personal travel, I think ongoing video visits might substitute for an occasional in person travel to see relatives and reduce emissions that way.

  8. Brian,
    Yes, I think some of that may continue, especially professionally. I think we’ve all discovered that it’s quite possible to have decent meetings, and conferences, remotely and some of that may well continue. My one concern is that once we are free to go out and mix and travel, that some may end up trying to make up for lost time.

  9. Len Dimmock says:

    The Kaya identity really isnt that helpful. Coal is as ever the key to emissions control and that means ensuring that the new build in China and India never gets used. Other than that we have a number of technical improvements which are on the way, including carbon captutre for carbonation which does look feasible at scale without having to bury CO2 underground. Renewables growth has looked minimal for a long time but exponential growth is going to make a big step this decade which will far outstrip GDP growth. Last year US renewable energy consumption exceeded coal for the first time since 1885 ( EIA ) . Electric cars on a global scale will make a significant dent in oil consumption this decade. Electrification in general is the byword and industrial decarbonisation overall has already been shown to be feasible by 2050 by the Energy Trasition Commission. Technical offsets from Direct Air Capture and Sequestration will come on stream at scale by the end of this decade for hard to treat areas like aviation. So we are about to see the fruition of a lot of work going on behind the scenes during this decade. The total cost looks to be much lower than originally thought and could well be much less than 1% of GDP. Together with the added improvements from lower air pollution etc this makes the transition an unarguable benefit. We will never get to 3C as the political pressure to use Solar Radiation Management will be irrestible well before then but the question is whether we can keep below 2C which still looks tough.

  10. Len,
    Yes, my impression is that there are indeed a lots of things going on that could well start having a big impact quite soon and that the costs will probably end being lower than might be expected. I’m slightly less confident about DAC and sequestration than you seem to be, but I may well be wrong. I hope we don’t end up seriously considering SRM, but I am aware that there is growing interest in it.

  11. David B Benson says:

    A variety of links on so-called geoengineering:

  12. Fearlessly treading way, way outside my expertise, I thought carbonation was primarily referring to the natural the fixing of CO₂ with concrete post-production. And calcination was the term for CO₂ emissions produced during cement manufacture.

    Although, it see at least one of the principals himself seems slightly confused on this detail.

    I think they were ultimately going for something like the Global Carbon Project “Fossil Fuel + Industry” category, or maybe just truly FF only (although how carbonation figures in that I don’t know).

    (and “calcining emissions” could apply to more than just CO₂ emissions from cem processes)

  13. jacksmith4tx says:

    We are going to terraform this planet.
    The only question is how our technology will do it? Will we use our god like powers to genetically modify our DNA and the biosphere to adapt to a changing environment? Or will we try to modify the climate with massive changes to global energy flows and the chemistry of the air and water?
    Likely both options are at play.

  14. As at the end of October 2020, via the Global Carbon Project and via Carbon Monitor, CO₂ emissions seemed tentatively to have recovered to (or exceeded) year before levels in most sectors. Ground transport a notable exception, and air transport a sm share to begin with.

    Preliminary numbers for the end of the year – aggregated up – seem to still see 2020 very slightly below December 2019.

    But my bet would be on post-Covid pent-up demand and catch-up, plus deliberate global stimulus to build all that steel and cement and PV’s and EV’s that we need to decarbonize – which ain’t building themselves with photons – to see 2019 eclipsed fairly soon. 2021, 2022. Even if we are (hopefully) in a longer secular plateau or decline.

  15. Carbon Monitor for daily-ish reporting estimates of CO₂ emissions.


  16. paulski0 says:


    Coal stopped increasing around 2010, mainly due to China

    It’s really mainly due to the rapid decline in US coal consumption rather than China’s coal plateau. Other OECD countries have contributed big declines too but if you only remove the US from global coal consumption figures 2018 and 2019 were new record highs according to the BP stat review.

    I did some simple modeling of coal consumption recently using the BP data, taking linear trends over 2013-2019 (chosen to make the best possible case for future coal decline) for each listed country and extrapolating those into the future. This produced a continuing slight decline up to 2030 but then a reversal with a new record high in 2039. This is because the countries with declining coal consumption are going to hit zero pretty soon while there is no such limit for the countries with increasing coal consumption. Nordhaus could win the bet without it necessarily meaning CO2 emissions have already peaked since they may begin to rise again after 2030.

  17. Chubbs says:


    I did oversimplify, and certainly the decline in the US coal use has been important. Let me clarify, between 2000 and 2013, China added roughly 3X US peak coal demand. If anything close to that rate of growth had been continued then coal use would not have plateaued.

    Regarding the future, I am relatively optimistic about future renewable competitiveness. These are manufacturing technologies on a learning curve; and the hard part, getting enough economic scale to be competitive, has already been completed. Note that improving renewable performance pressures all fossil fuels, which will tend to improve the competitiveness of gas vs coal, as coal’s fuel price advantage will be minimized. Of course I could be wrong, but resumption of coal growth would not be a good lead indicator. Already coal does more environmental damage than any economic value returned. That will only worsen in the future as the cost of carbon damages escalates.

  18. Ben McMillan says:

    I also agree with ‘Kaya Identity not very helpful’.

    You’ve taken one thing that is hard to predict and somewhat arbitrarily turned it in two or more things that are possibly even harder to predict/understand.

    e.g., people spending extra money on stuff that doesn’t have much embedded energy versus jetting around the globe is not in normal terms a form of ‘efficiency’ (or a bad thing per se). Energy demand is not necessarily very elastic. The relationship between ‘GDP’ and ‘energy’ is pretty wobbly.

    Sector-by-sector type analysis seems much more solid as a way of making predictions. It also provides a path to envisioning a future that actually allows climate stabilisation consistent with a desirable lifestyle.

    Whereas the Kaya Identity seems to lead you into the “climate vs. the economy” frame. Posing them as at odds.

    Worrying about ‘health vs. the economy’ was certainly pretty counterproductive last year.

  19. I agree that the Kaya Identity isn’t particularly useful. In fact, there are some who use it in very unhelpful ways (pretending it can be used to predict emissions, rather than it simply being a truism). I was just trying to illustrate that there are a number of different factors that influence emissions.

    Whereas the Kaya Identity seems to lead you into the “climate vs. the economy” frame. Posing them as at odds.

    Worrying about ‘health vs. the economy’ was certainly pretty counterproductive last year.

    Yes, this is a fair point.

  20. mrkenfabian says:

    I don’t know how things will play out so I am okay with setting targets ahead of having the plans to reach them, even when applying what we have now falls short of being able to get us to net zero emissions. Any plan with costings will be wrong. Way wrong if we are lucky.

    Wind and solar and batteries are sidestepping the political partisan pile-up – or else we’d be paying much more serious mind to those high emissions scenarios; I think it would not even be a question of hitting anywhere close to net zero without their having exceeded all expectations. Solar on rooftops kills alarmist fear wherever it is installed. And if current iterations of these technologies are cost competitive in large parts of the world – and it is clear they are – then next iterations will only reinforce an emerging dominance of new electricity generation. And I cannot help but feel some optimism as a consequence; as the proportion of low emissions electricity grows it is not just households making less emissions because the embedded emissions of manufacturing are reduced. Including those emissions from manufacturing RE tech.

    If resource alarmists turn out right and limitations for RE do prove intractable – and I think resource limitations are inevitable – I would expect it to become apparent in commodity markets with sufficient warning to re-assess. It is a constantly moving target but not even legislated targets will stay legislated if – but I have this hope, based on the existence of lots of scientists and engineers and entrepreneurs, major investors as well as legions of minor innovators, all not waiting for others to do it for them, that we ain’t seen nothin’ yet!

  21. mrkenfabian, I believe you have found a winning formula, restating what I have argued for more than a decade. You must change the political climate first, and positive experiences by the polity are the first step to doing that.

  22. John Hartz says:

    ATTP et al: Happy New Year!

    Needless to say, the headline and sub-headline of this ICN article caught my eye and piqued my interest.

    Many Scientists Now Say Global Warming Could Stop Relatively Quickly After Emissions Go to Zero That’s one of several recent conclusions about climate change that came more sharply into focus in 2020 by Bob Berwyn, InsideClimate News, Jan 3, 2020

    The final section of Berwyn’s article, Making it Stop, reads as follows:

    Some scientists punctuate their alarming warmings with hopeful messages because they know that the worst possible outcome is avoidable.

    Recent research shows that stopping greenhouse gas emissions will break the vicious cycle of warming temperatures, melting ice, wildfires and rising sea levels faster than expected just a few years ago.

    There is less warming in the pipeline than we thought, said Imperial College (London) climate scientist Joeri Rogelj, a lead author of the next major climate assessment from the Intergovernmental Panel on Climate Change.

    “It is our best understanding that, if we bring down CO2 to net zero, the warming will level off. The climate will stabilize within a decade or two,” he said. “There will be very little to no additional warming. Our best estimate is zero.”

    The widespread idea that decades, or even centuries, of additional warming are already baked into the system, as suggested by previous IPCC reports, were based on an “unfortunate misunderstanding of experiments done with climate models that never assumed zero emissions.”

    Those models assumed that concentrations of greenhouse gases in the atmosphere would remain constant, that it would take centuries before they decline, said Penn State climate scientist Michael Mann, who discussed the shifting consensus last October during a segment of 60 Minutes on CBS.

    The idea that global warming could stop relatively quickly after emissions go to zero was described as a “game-changing new scientific understanding” by Covering Climate Now, a collaboration of news organizations covering climate.

    “This really is true,” he said. “It’s a dramatic change in the paradigm that has been lost on many who cover this issue, perhaps because it hasn’t been well explained by the scientific community. It’s an important development that is still under appreciated.” “It’s definitely the scientific consensus now that warming stabilizes quickly, within 10 years, of emissions going to zero,” he said.

    The Covering Climate Now article referenced in the above can be accessed here: https://www.cjr.org/covering_climate_now/michael-mann-60-minutes-emissions-warming.php

    This piece of “good news” flew under my radar screen in October, It seems relevant to this discussion. That is why I bring it to your attention here.

  23. “Many Scientists Now Say Global Warming Could Stop Relatively Quickly After Emissions Go to Zero ”

    I think a lot of folks also say global warming could stop immediately when the Supreme Being snaps fingers and returns us to a climate state closer to the Garden of Eden.

    I am not confident about either plan to stop global warming. Both seem predicated on an unlikely event. I could be wrong. I would love to be wrong.



  24. Ben McMillan says:

    Happy new year to all, unless it is too early for you!

    Likely trajectory of the anglophone world + Europe seems like it will be a continued moderate downward trend but the big uncertainty is the East (as already alluded to earlier).

    Not clear the participants in this debate most visible to us, mostly in the Anglophone world and Europe, have a strong grasp on where Eastern countries are going. China, but also rest-of-Asia is equally important.

    A bit like in Australia, the provinces of China seem to have very different policies/incentives to the central Government. What does that mean over the next decade? What about other countries in Asia?

  25. izen says:

    It looks like the producers are on the side of Ken…

    “Currently idling 7.2 million barrels a day, or about 7% of world supplies, the producers have resolved to return a further 1.5 million barrels a day in carefully calibrated installments.

    Russian Deputy Prime Minister Alexander Novak has signaled his readiness to proceed, saying last month that prices are in an optimal range of $45 to $55 a barrel. If OPEC+ refrains from bolstering exports, its competitors will simply fill the gap, he said.

    “The market needs the oil,” said Jan Stuart, a global energy economist at Cornerstone Macro LLC. “The prevailing view in OPEC+ seems to be that you have to go for market share. You cannot subsidize the return of U.S. shale.”

  26. JH,

    Many Scientists Now Say Global Warming Could Stop Relatively Quickly After Emissions Go to Zero That’s one of several recent conclusions about climate change that came more sharply into focus in 2020 by Bob Berwyn, InsideClimate News, Jan 3, 2020

    Some of us have been saying this for a few years. I think I wrote a post about this in 2016, Realclimate had a post in 2010, and the first papers on this were in about 2008.

  27. Willard says:

    Rings a bell:

  28. India and China want and need development, but can they do that with decreasing carbon intensive, in a more than compensatory way? And can those countries with the greatest historic cumulative emissions act fastest, to help those needing development? Do developing countries aspire to the ‘wests’ high levels of consumption?

    People suggest that because carbon emissions haven’t fallen ‘that much’ during lockdowns, so consumption can’t be that much part of the problems. But of course, end use of goods and services is just part of a energy intensive supply chain. Just because an end-use part of it may swtich off, doesn’t instantly stop it all.

    It concerns me that we might project trends based on essentially doing the same things as we do now but in an increasingly decarbonised form (e.g. moving to EVs)? Rather than say a completely transformed civic landscape where personal car ownership becomes redundant.

    Even how we measure development is an issue (e.g. GDP per capita). New Zealand appears to be one country exploring wellbeing as a better measure of development …


    Covid-19 has revealed that those most at risk are often those who are already disadvantaged – in Maslow terms, they don’t have even the minimum needs met. Climate impacts are and will be just as unjustly spread.

    The Kaya identity is emblematic of the narrow nature of the peak carbon debate, because it seems to leave out another kind of externality: system change.

  29. Richard,
    I guess I’ve always seen the Kaya Identity as a truism. I certainly wasn’t suggesting that the only way to think of how we might reduce emissions is through changes in energy intensity, or carbon intensity. However, I suspect that one could always frame changes in CO2 emissions in terms of changes to energy intensity and carbon intensity, even if these do over-simplify what is happening, or what could happen.

  30. I don’t disagree with that. I was just musing on how to broaden the discussion beyond 2 or 3 levers.

  31. Glen Peters (again via Carbon Monitor) updated the running CO₂ emissions through October (mine above was actually through September, as I look at).

    I think it’s actually quite telling that emissions seem to have recovered faster than the global economy as a whole in power, industry and residential.

    I’ll just add to my “case” above for increasing emissions is the fact that we’re heading into 2021 with more ICE vehicles on the road, more buildings built with gas, on and on. And adding more daily. These are intended to be used as designed. i.e. burn fossil fuels. The committed emissions dilemma. Are power plant retirements, etc., enough to offset all these countervailing forces, I guess we’ll see.

    Switching from “committed emissions” to the “committed warming” detour. Peak emissions don’t actually have much, if any, relation to peak warming, which is (effectively) determined by (ultimate) cumulative (net positive) emissions, irrespective of when when they occur.

    Peak emissions are of some interest (other than “A Victory!”) of themselves because they allow you to take the integral of future emissions pathways from that point, something Alice Bows and others were discussing, yes around 2008.

    Maximum warming *rate* might be sometime within the next 10 years after peak emissions, depending on how pre- and post-curves look, I guess, and the non-anthropogenic contributions.

    Gosh, I clicked on Ken’s article about Caldeira and Ricke on maximum warming, and saw he linked to Steve Easterbrook’s 2013 blog about the zero-emissions commitment warming. That was based on a visiting lecture that Damon Matthews gave us at UofT. I was somewhat stunned by the import of what I thought (correctly) he was saying. I still have all the pictures I took of those slides.

    Eight years ago next month. 😳🤔

  32. Richard,

    I don’t disagree with that. I was just musing on how to broaden the discussion beyond 2 or 3 levers.

    Yes, that is a good point.

  33. Rust,

    Eight years ago next month. 😳🤔

    Yes, some have been pointing this out for quite some time 🙂

  34. 51 slides, including transitions on the slides, and a very young-looking, ponytailed Damon Matthews.

    I think I will make a thread of them for posterity’s sake on twitter. Glancing at them, they are still quite easy to follow (easier having incorporated after the fact!).

    You had another 2020 blogpost on an excellent recent by Damon and team, Ken.

    I like to point out that he was lead author on one of the (the?) first papers↓ pointing out the necessity of zero emissions (2008) and one the first papers↓↓ articulating the linear proportionality of temperature increase to cumulative carbon emissions (2009) (which so many people still seem to get wrong because they had to memorize ΔF = 5.35 ln (C/C₀) for an exam once or something?)

    Not bad!


    Back to “2019 peak in emissions?”! 👍

  35. Rust,
    Thanks, I thought I was probably missing a paper.

  36. Ben McMillan says:

    Per capita CO2 emissions are now not dramatically different in China vs the UK or vs the EU, even when you account for embodied emissions (China sending us stuff). They are all slightly, but not hugely above the world average. So it isn’t ‘destiny’ that China in particular should increase emissions.

    And although e.g. India and most of Africa have a lot of catching up to do, they hopefully won’t adopt the profligate lifestyles of Australians, for example, and could end up closer to the falling EU average in ten or twenty years time.

    The plan is contract and converge, where these less developed nations are ‘allowed’ to bring their per-capita emissions up towards the falling emissions in rich countries, and then everyone falls to net zero on a similar curve.

    Hard to see anything much better than a plateau in emissions happening though (unless a lot of places step up their game/clean tech keeps getting a lot cheaper and better) which should keep the bet interesting.

  37. John Hartz says:

    ATTP: I’m pleased to see that you’ve been on top of the issue addressed in my previous comment re the article:

    Many Scientists Now Say Global Warming Could Stop Relatively Quickly After Emissions Go to Zero. That’s one of several recent conclusions about climate change that came more sharply into focus in 2020 by Bob Berwyn, InsideClimate News, Jan 3, 2020

    Berwyn and Mann obviously believe there are still people put there making outdated, incorrect pronouncements. .

  38. mrkenfabian says:

    I don’t think frugality will ever be popular enough to make reducing energy consumption a viable and successful climate/energy policy – the rhetoric around extremists forcing us back to the stone age has been unhelpful enough that I don’t think climate activists do us favours by making going without stuff the principle policy approach. It sure won’t work if it purely voluntary and responsibility to do so can be evaded by the simple expedient of denying the problem is serious.

    We may – likely will – face reduced per capita consumption but it will be by rising costs, not by choice; it will happen despite efforts to the contrary. Aiming for energy abundance using low emissions tech makes more practical sense than all the calls for remaking our societies. The former is a real option that we can pursue, for all that it doesn’t give certainty, but we can be certain the latter is not really an option.

    I don’t know if the solar on my roof would be enough for powering an EV from what currently gets exported to the wider grid, but suspect so; I send much more energy to the grid than I use. I foresee more EV chargers than we ever had parking meters; it is advantageous for grid operators that EV’s are connected whenever unused, for varying charging rates to smooth system variability and to access to some portion of the stored power (under agreed, equitable terms). I also expect to have a single electricity account, that is not tied to any specific location. Deducting household PV contributions to the grid from EV charging at other locations – less some service fees – means we will charge them with our own solar wherever we go.

    Private vehicles offer that possibility but freight transport needs different approaches. I think electric road freight may need swappable battery packs. This also provides the potential for a lot of plugged in batteries grid operators can use – the batteries will spend time “parked”, even if the vehicles themselves cannot afford to sit idle.

  39. mrkenfabian says:

    Seems to me if we get to very low emissions SOON we might expect warming to stop. The longer it takes the more likely carbon feedbacks will put that scenario forever beyond reach.

  40. JH,

    Berwyn and Mann obviously believe there are still people put there making outdated, incorrect pronouncements. .

    They’re certainly correct about that.

  41. Chubbs says:

    Renewables are increasing energy supply and competition, so frugality is not needed. Quite the opposite, I foresee increased energy supply and lower cost during the transition away from fossil fuels. It is the highest cost fossil fuel projects that will be dropped first, as renewables increasingly become the price setter.

  42. Ben McMillan says:

    I think it might be a little premature to proclaim clean tech will solve all the problems, and frugality is not necessary. Things like meat and air travel are tricky, and there are other planetary boundaries than just CO2 emissions.

    A bit of frugailty would make everything easier and faster.

    On another topic: I think freight operators will embrace EVs quickly because money.

  43. paulski0 says:

    Looking at various emissions projections based on full implementation of NDCs there seems to be a robust expectation that 2030 will be no higher than now (or 2019). In terms of the details of the bet that could still entail an initial rise followed a drop to 2030, plus year-to-year variability, so I think Ken Caldeira would still be favourite on this basis. That still wouldn’t automatically mean emissions have peaked though – the majority of models indicate that further policy strengthening would be required to prevent emissions rising again after 2030, though it seems reasonable to expect that strengthening would happen.

    Regarding the socio-economics required, those projections generally assume a median-type (e.g. SSP2) scenario, with reasonable economic growth in poorer countries, so I don’t think that’s necessarily an issue. One thing about the Kaya identity decomposition is that GDP generally anti-correlates quite strongly with Energy/GDP, so high GDP growth is typically associated with high rate of energy efficiency improvement. There is also some anti-correlation between GDP and population growth, though that’s a little more complex. So it’s not necessarily the case that higher GDP growth means higher emissions. This is also why we shouldn’t assume climate damages would reduce emissions. It’s plausible that such damages would slow energy efficiency improvements and halt fertility rate declines in poorer countries.

  44. Chubbs says:

    Ben – Let me be clear, clean energy isn’t a panacea. I am mainly interested in disabusing the notion that fossil fuels are essential for future well being. Frankly, I foresee exactly the opposite. Over reliance on fossil fuels is an increasingly risky strategy, just ask any stock market investor.

  45. Ben McMillan says:

    Chubbs: Yep, the good correlation between growth and green tech, and fossil fuel companies performing badly as investments, is problematic for the idea that fossil fuels/CO2 emissions are linked inextricably to growth (PaulS’ points above, also relevant here). At some point, fossils fuels are just a relic tying you to the past.

    As you get wealthy or decarbonise things like electricity and transport, there is an increasingly narrow emissions-intensive sector of the economy, whose growth is less well correlated to overall economic health, and broad-brush analyses become less informative.

  46. Ken says: “if we get to very low emissions SOON we might expect warming to stop…” (or at least slow way down)

    Yes, exactly right. and that is the right point and an argument that is worth making and publicizing and maybe even betting on. A public bet about when we hit peak emissions (minus carbonation?) is a distraction and suggests that simply hitting the peak in emissions is a particularly important milepost. (Covey’s 2 habit: begin with the end in mind, envision your goal clearly so you can work toward it effectively)

    Some questions arise from Ken’s statement for me: What is “very low emissions?” I would suggest an annual increase of 0.5 ppm to atmosphere would indicate we have hit very low emissions and are well on our way to a net zero state. That is a meaningful target – very low emissions, well defined.

    When do we hit very low emissions and what will our atmospheric CO2 number be at that point? These two considerations are linked, so as the atmospheric CO2 level continues to rise, the time to hit a state of very low emissions shortens up.

  47. Willard says:

    Via Zeke:

  48. “New calculations published in the journal Nature Climate Change estimate that warming based on emissions that have already happened, called “committed warming,” will cause the planet to heat up by between 2.3 degrees celsius and 2.8 degrees celsius when compared to pre-industrial levels.”



    How do we reconcile/evaluate the “committed warming” discussed in this study and article with the Berwyn and Mann view?

    are Zhou et al making outdated, incorrect pronouncements?

  49. small,

    How do we reconcile/evaluate the “committed warming” discussed in this study and article with the Berwyn and Mann view?

    It’s pretty easy to reconcile this. The Zhou et al. paper is looking at constant forcing commitments (all forcings constant at today’s level, or long-lived forcings constant at today’s level). This tells us how much we’d warm if the forcings remained constant at today’s level. This is not the same as the zero-emission commitment, which is what is being presented in Bob Berwyn’s article. If we got emissions to zero, the forcings would actually decrease as the natural sinks continued to take up some of our emissions.

    So, the general picture is that the zero emission commitment is probably small (i.e., we won’t warm much if we stopped all emissions now) while there is still a warming commitment if we fix concentrations/forcings at today’s level. The paper is mainly pointing out that the pattern effect might suggest that this is slightly larger than we had thought. This may also impact the zero emission commitment, but my impression is that the zero emission commitment would still probably be quite small.

  50. Willard says:

    I looooove paper explainers:

  51. John Hartz says:

    ATTP: After seeing the below AP News article, I came here to pose the same question to you as did smallbluemike. Thank you for your rapid response to SBM.. Given the MSM interest in the new research findings, perhaps this ball-of-wax deserves a new OP?

    Global Warming Already Baked In Will Blow Past Climate Goals, a New Study Says by Seth Borenstein, Science AP News, Jan 5, 2020

  52. John Hartz says:

    Willard: Thank you for posting the “paper explainer” video. It is the first one that I have seen. Are there others?

  53. Zeke’s Twitter thread is also good.

    There does still seem to be confusing as to whether commited warming refers to how much we would warm if concentrations remained constant, or if we emissions went to zero. It’s probably worth starting to be more specific and to use “constant concentration warming commitment” or “zero emission warming commitment”.

  54. John Hartz says:

    ATTP: Seems to me that the WMO/UNEP ought be clarifying what the research is saying and defining new terms as need be. This should happen ASAP. If climate science wonks like myself are confused, you can bet your sweet bippy that climate journalists, politicians and others are as well.

  55. John Hartz says:

    ATTP: I’ll also bet you that Zeke Hausfather will write an article about this ball of wax for Carbon Brief. (I have no inside information.)

  56. thanks for the reconciliation. you say, ” If we got emissions to zero, the forcings would actually decrease as the natural sinks continued to take up some of our emissions.”

    I have two problems with this statement. I sort of thing that the chances of human beings getting to zero emissions by any set date, say 2040, or 2050, or even 2100 are about the same as the chance that a supreme being will suddenly step in and just sweep away the ghg emission problem with a snap of his/her fingers. Either of these situations seem very unlikely to me.

    Second, you say the forcings would actually decrease as the natural sinks take up emissions, but it’s really more accurate to say that if emissions suddenly fell to zero, either through human or divine action, the forcings would decrease to the extent that the natural sinks continue to work at the level of CO2e that exists at the moment when the zero emission miracle happens?

    Sorry, I have real world concerns with the Berwyn Mann calculation. I get their position better and can reconcile it more easily with Zhou et al after your explanation, but since this post started with discussion of a bet between Caldeira and Nordhaus, I would be happy to take on any betters who think that we will see the Berwyn Mann state of zero emissions or the divine intervention emission solution before 2050. Any takers? Anybody feel like betting that the Berwyn Mann state is anything more substantial and likely than the divine intervention solution?



  57. I think there is some confusion about the idea of committed warming and the level of emissions and with some good reason.

    Seth Borenstein at AP News says this: “A new study says the amount of global warming already baked into the air because of past carbon pollution is enough to blow past internationally agreed upon climate limits. A study on Monday, Jan. 4, 2021 takes a different look at what’s called committed warming that comes from heat-trapping gases staying in the atmosphere for more than a century. (AP Photo/Charlie Riedel, File)”

    If I am understanding this right, I think that committed warming really refers to the amount of warming that will result from a net zero condition where our continuing emissions are offset by natural sinks and whatever emission technology we can deploy combine to stop the increase of CO2e in the atmosphere.

    Berwyn and Mann’s vision of a zero human emission planet would be expected to stop the increase in warming rather quickly. The vision of a zero human emission state is much harder to reach than a net zero state where we might be able to stop the increase of CO2e in the atmosphere.

    If I have any of this wrong, please spell it out for me.



  58. small,
    The point is that we’re using the same term “warming commitment” for more than one thing. Technically there is a “zero emission warming commitment” which is what Mann and Berwyn are referring to, and a “constant concentration commitment” which is essentially what is being presented in the new Zhou et al. paper. They’re different and have different results. In a zero emission scenario, there is probably little warming commitment (along on long timescales, ice sheet retreat and sea level rise could change this) while in a constant concentration scenario there is still a reasonable amount of warming baked in.

  59. Ben McMillan says:

    What would be really helpful is a graph of the modelled temperature response, with and without the ‘pattern effect’: is there one around somewhere? (I didn’t see any in the paper). As Dessler states in the video, most of the excitement happens centuries into the future, the estimated pattern effect in 2100 is quite small.

    In a zero-emissions scenario, the temperature actually slowly starts falling around about 2200 anyway.

  60. Ben,
    I think there is still a bit of uncertainty about the zero emission commitment (ZEC). We could still warm a little, or could cool a little. However, as far as I’m aware, none of the models used to estimate the ZEC include things like dynamic ice sheets, so there could be long-term feedbacks that are not really considered that could somewhat amplify the warming. On the other hand, on very long timescales, atmospheric CO2 is also drawn down by the slow carbon sinks, so I don’t know how these long-terms effects will play out.

    My own view is that it’s worth being aware that on ~100 year timescales, the likely zero emission commitment is quite small. On ~100 year timescales, we’re not commited to lots of future warming if we get our act together, start reducing emissions and get to (net) zero as soon as we reasonably can.

  61. Ben McMillan says:

    I think that focusing on the ~100 year timescale would be helpful. There does seem to be a lot of uncertainty about what happens on millenial timescales but that seems, frankly, much less important to our current pickle.

  62. John Hartz says:


    Given how rapidly the human race is decimating the biosphere through manmade climate change, plastic pollution, chemical pollution, etc.,, I wonder if anyone will be around to observe the Earth’s climate system in 2121.

  63. Ben McMillan says:

    Dessler again giving context about timescale:


    Some real facepalms in that article though. For example this bit of the article (as of 7AM thismorning, maybe someone will notice+corrrect):
    ‘Climate models run by scientists on future temperatures were based on a certain carbon dioxide concentration in the atmosphere. If this remained at the current high level there would be runaway climate disaster, with temperatures continuing to rise even if emissions were reduced because of a lag time before greenhouse gases accumulate in the atmosphere.’

    I’m more and more agreeing with John’s statement that there needs to be an established standard for ‘committed warming’, ideally on a relevant timescale, rather than t->infinity.

  64. There is *extensive* definition and discussion of various “warming commitment” concepts and model experiments in each of IPCC AR4 (2007), IPCC AR5 (2013), and IPCC SR1.5 (2018).

    I am going to excerpt a short part of IPCC SR1.5, which discusses just the “constant composition commitment” and “zero emissions commitment”, and largely just in the context of the Paris 1.5°C target (reflecting the mandate of the SR1.5).

    But note well the reference to Meehl, et al., 2007, (IPCC AR4 WGI, Chapter 10, Global Climate Projections), which discusses various *other* “commitment” categories (and other standardized model experiment runs in general, such as idealized ongoing 1% yr⁻¹ CO₂ emissions increases, etc.).

    AR5 has good discussion as well, but I just mention AR4 to (i) highlight the “not-newness” of these concepts, and (ii) because, although AR4 does not have an explicit statement of “ZEC ≈ 0°C”, if you look carefully at some of the model experiments they examined, this is largely evident even then(see IPCC AR4 WGI Figure 10.3.5, attached at the end of this post).

    First, here is the (brief) IPCC SR1.5 excerpt:

  65. Chubbs says:

    Good discussion. Important to be clear on what is being committed too. Neither of the two options is ideal for the following reasons: 1) we can’t drop emissions to zero quickly; 2) The lifetime of the climate-active constituents is different so impossible to maintain a constant composition. For CO2 alone and as long as emissions are elevated, the constant composition isn’t bad. Stabilizing at roughly current CO2 is probably the best we can hope for.

  66. Ben McMillan says:

    To put it less prescriptively, ‘how do you have a sensible public discussion of this stuff when there are so many standards?’. If some authors pick whatever definition that gives an exciting result in the year 2500, then you end up with a merry-go-round of ‘climate change worse than expected’ in the newspapers but it is likely to be misleading.

  67. ” we can’t drop emissions to zero quickly”

    “how do you have a sensible public discussion of this stuff when there are so many standards?’”

    “Stabilizing at roughly current CO2 is probably the best we can hope for.”

    “there needs to be an established standard for ‘committed warming’… on a relevant timescale”

    I am pleased to see this discussion move in this direction. It certainly makes sense to me because it helps dispel confusion and allows/encourages us to pursue a sensible discussion about our real world plight. Such a discussion might help a larger population understand what needs to be done, how fast it can be done and why it needs to be done.

    I understand that academics may be interested in the Berwyn and Mann calculation that warming would stop if emissions suddenly went to zero, but when that calculation and discussion leak into the news cycles as part of a discussion about committed warming, I think the general population and BAU enthusiasts will fix on that factoid and that factoid will reduce our collective willingness to embrace the changes that need to be made.

    I think whenever the Berwyn and Mann calculation arises, sensible people should ask: and how do you calculate that we will reduce emissions to zero and when will do you calculate that reduction process will be complete? I think there are a lot of angels dancing on the head of a pin with that model scenario.



  68. But Paris Agreement (not commitment 😂) is “well below 2°C”. And the IPCC SR1.5 is quite straightforward (with error bars) about the cap future *cumulative* emissions that requires.

    Neither of the two headline-grabbing “developments” this week (one just saying something we’ve understood for years) had much to do with that at all (except the obligatory add at the end on the imperative of “reducing emissions”).

    I actually feel that it would be *really* helpful if most people had something like the IPCC SR1.5 66% post-2017 CO₂ budgets for 1.5° and 2.0°C bolted in their minds and look for changes in those before flip-outs. And not much else, unless they really choose to get into the weeds of carbon budgets.

    Although, at 420 and 1170 GtCO₂ respectively – now already reduced by 30% (😳) and 11% in just the three years hence – might startle the horses. But I am not even sure the “net-zero by 20xx” framing is conveying to people what is really implied about how fast the budgets are being exhausted in the absence of really dramatic near-term reductions.

    “Really” simple 👇, but for 1.5°C / 66% budget – from SR1.5 just over 2 years ago – the blue is historical emissions to end-2017, orange is actual emissions 2018-20, and grey is “what’s left”. (And “some people” are simultaneously adamant about 1.5°C and vehement against CDR… mmm… ‘kay)…

  69. Willard says:

    > I think the general population and BAU enthusiasts will fix on that factoid and that factoid will reduce our collective willingness to embrace the changes that need to be made.

    In fairness, you always think that, Mike. Over and over again. On every subject AT may bring.

    At some point I think we need to let go of trying to implicate scientists for that collective unwillingness, more so if we don’t read what they write.

  70. ““This falling atmospheric CO2 causes enough cooling to balance out the warming ‘in the pipeline’ due to slow ocean heat uptake, and global temperatures remain relatively flat after net-zero emissions are reached,” said Zeke Hausfather”


    In the real world of a net zero emissions scenario, how does atmospheric CO2 fall? All human economy is going to push for recognition of a net zero condition as the situation where atmospheric CO2 stops increasing. A level and form of human economy where atmospheric CO2 starts to fall sounds like a minus zero emissions scenario to me. I am in favor of a minus zero emissions scenario, but I am not sure how and when we will get there and I think it makes sense to identify that model scenario in an accurate manner.




  71. at willard: Sure, that is what I think about human beings. But I encourage you to play the ball, not the man. Do you think it is accurate to describe a situation where atmospheric CO2 falls as a net zero condition?



  72. Willard says:

    No need to bait me, Mike.

    There are other resources than papers if you can’t read them:

    If scientists worked 10% as much as climate scientists to communicate their results, the world would be a better place.

  73. [Playing the ref. -W]

  74. David B Benson says:

    John Hartz, thank you for the links.

  75. David B Benson says:

    Half again that of the 18th century; back to the future.

  76. Willard says:

    At a similar latitude than Uganda:

    Not exactly a science paper explainer, but in some ways better as it features real people.

  77. I think it makes sense to focus on the CCC – constant composition commitment – of global warming as an intermediary step in determining the urgency for further change. Thanks to the graphic above from RNS that helped me understand CCC. If I understand CCC correctly, there would be additional warming “baked in” to our global situation. Wouldn’t it be great to achieve the CCC state where atmospheric CO2 is stabilized around 415 ppm? At that point, we would be able to gather observational data to resolve the level of “baked in” warming that we are facing and that could help us determine how fast we need to move from the CCC state to the ZEC state.

    Like most of us here, I live in a safe part of the developed world and I can probably stand a bit of baked in warming without suffering too much. The Ugandans like Vanessa Nakate may need to be patient and suck it up a bit as we negotiate these changes. I think we have some sense of the suffering of the Ugandans, but I am not sure they are sufficiently aware of our concerns about wrecking the world economy to bring them relief as quickly as they may desire.
    It is a balancing act, is it not?

  78. Bob Loblaw says:

    “It is a balancing act, is it not?”

    You do realize how what you are saying can be interpreted as “me losing money is just as important as you losing your life”?

  79. Yes, Bob. I realize that is what I am saying. The balancing act argument is a position that is asserted over and over by folks who feel that we need to be careful and not over-react to the implications of climate science.

    I will repost a quote from above: “it’s worth being aware that on ~100 year timescales, the likely zero emission commitment is quite small. On ~100 year timescales, we’re not commited to lots of future warming if we get our act together, start reducing emissions and get to (net) zero as soon as we reasonably can.”

    It is a balancing act. We need to get our act together and get to net zero as soon as we reasonably can. People will die in either case. If we act too quickly, in an unreasonable manner, folks in our own communities may die from the impacts of disrupting our economy and if we act too slowly, in an unreasonable manner, more folks will die in countries like Uganda.

    I have family in Uganda and South Sudan who are indigenous Africans. I am not unaware of their situation. My Africa-connected family members who live in the developed world send money to Uganda and South Sudan on a regular basis to help our family members stay alive, pay for housing, pay for medical care and groceries. I have been working on immigration paperwork for my daughter in law and grandson since November 2019 to allow them to come to the US from Kampala. It has been very slow and frustrating because the US embassy staff have closed their doors to protect themselves and have slowed the process to allow these family members to join us here in Western Washington. We have wanted to get those two here before the covid pandemic blasts through Kampala. I think we are getting close to that goal. I will breathe a sigh of relief when I know that Nyandeng and Atem are on a plane in route to the US.

    My son Dhieu and his family in Juba don’t want to leave. He is a professor and administrator at the Univ of South Sudan and a US citizen. Those family members can jump on a plane anytime they decide it must be done and join us in the safety of Western Washington, but I know that David/Dhieu does not want to abandon his work to raise up the indigenous people of South Sudan, so I don’t think they will return to the US in my lifetime. I miss Dhieu and have never met his wife and daughter, but I completely respect and largely agree with the decisions that Dhieu and Akwet are making to remain in Juba with their daughter Atong.

    Life is a balancing act, is it not?


  80. small blue mike, I wish your family the best of good fortune in their real, attempted and future movements.

  81. How much of what you refer to as ‘baked in climate commitments’ is in fact just an acknowledgement of the sluggish response of the hydrological system to changes in inputs?

  82. Tom,
    The issue is essentially that if you consider how much we would warm if we held atmospheric CO2 concentrations fixed, then we do continue to warm because of the large heat capacity of the oceans. On the other hand, if we stopped all emissions, then the natural sinks would continue to take up some of our emissions so that this roughly balance this continued warming (i.e., global surface warming would roughly stabilise if we halted all emissions).

  83. Bob Loblaw says:

    folks in our own communities may die from the impacts of disrupting our economy “

    Folks in our own communities dying is a long way from folks in our own communities having to settle for a 40″ TV instead of the 70″ one, or share one car in a family instead of have one for each parent and child. Your relatives in Uganda or the Sudan probably have a lot less they can give up before there are no meals on the table (if they have a table).

    Too many of the “we can’t harm the economy!” arguments fall in the “I want! I want! I want!” class of discourse that may be cute coming from a 4-year-old, but is pretty sad coming from adults.

    The GDP is not GOD.

  84. mrkenfabian says:

    However it came about, the bottom line (here in Australia) appears to be “Must not harm the economy”, or more directly, “Must not raise costs of businesses doing business” (eg the Business Council of Australia position).

    Worse, I suspect (cynically) the BCA may not really mean “must not raise costs on average” but actually means “raise costs for ANY individual business”, perhaps even especially for those most dependent on fossil fuels. That is also “must not raise costs” based on accounting that excludes climate costs, ie with embedded cheating. The BCA makes very nice statements of in-principle support for things like carbon pricing – and vigorously opposes all proposed policy to do so. Being cynical comes all too easily.

    I also note that with respect to direct subsidies there is a equivalent “must not harm the economy” provision there also – “must not raise taxes”; ie governments can subsidise clean energy as much as they like, but only without raising any extra revenue to do so, especially not any taxes tied directly to emissions. Australia’s pro coal and gas government appears to only agree to subsidy support for clean energy (not something they ever advocate themselves, but rather, unable to resist) when tied to equal or better subsidy support to Australia’s fossil fuel industry.

  85. Willard says:

    À propos of nothing, incredible thread:

  86. *Very* preliminary CO₂ emissions data for 2020. (From new-kid-on-the-block Carbon Monitor.)

    COVID curbed carbon emissions in 2020 — but not by much

    Jeff Tollefson, Nature, 15 JANUARY 2021

    “Despite sharp drops early in the pandemic, global emissions of carbon dioxide picked up in the second half of the year, new data show.”
    “Researchers published emissions data for the first half of 2020 in October, but provided a complete set to Nature this week.”

    2021-22 – and whenever stimulus kicks in – will be very interesting as whether 2019 is peak.

    It does appear that there’s a lot of auto-pilot/committed emissions out there.

  87. “It does appear that there’s a lot of auto-pilot/committed emissions out there.”

    Yes, that appears to be the case, but there is little or no committed warming once we hit net zero, so we should get serious and reduce to net zero as as quickly as we reasonably can.

    I think you can see the reasonable efforts that have been made so far and how much they have slowed the increase of CO2 in atmosphere and oceans. We need to keep up the good work!



  88. fgsjr2015 says:

    Whether it’s Europe’s hottest year on record, unprecedented wildfires in California/Cascadia, unprecedented stalling hurricanes, off-the-chart poor-air advisories, the mass deforestation and incineration of the Amazonian rainforest (home to a third of all known terrestrial plant, animal and insect species), record-breaking flooding in Europe, single-use plastics clogging life-bearing waters, a B.C. (2019) midsummer’s snowfall, the gradually dying endangered whale species or geologically invasive/destructive fracking or a myriad of other categories of large-scale toxic pollutant emissions and dumps—there’s discouragingly insufficient political gonad thus little/no will to adequately address the cause-and-effect of manmade global warming and climate change.

    To me, our existence has for too long been analogous to a cafeteria lineup consisting of diversely societally represented people, all adamantly arguing over which identifiable traditionally marginalized person should be at the front and, conversely, at the back of the line. Many of them further fight over to whom amongst them should go the last piece of quality pie and how much should they have to pay for it—all the while the interstellar spaceship on which they’re all permanently confined, owned and operated by (besides the most wealthy) the fossil fuel industry, is on fire and toxifying at locations not normally investigated.

    The latter is allowed to occur, because blue-shirted liberals and red-hatted conservatives are preoccupied loudly blasting each other for their politics and beliefs thus distracting attention from big business’s moral and ethical corruption, where it should be focused.

    Meanwhile, mindless arguments are made, and stupid-sounding catchphrases are uttered, like “It’s the economy, stupid!”

    In short, we’re distracting ourselves from our own burning and heavily polluting of our sole spaceship, Earth.

    What is sufficiently universal, however, is that the laborers are simply too exhausted and preoccupied with just barely feeding and housing their families on a substandard, if not below the poverty line, income to criticize the former for the great damage it’s doing to our planet’s natural environment and therefore our health, particularly when that damage may not be immediately observable.

    (Frank Sterle Jr.)

  89. Pingback: Have CO2 emissions peaked? – Site Title

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