CO2 emission reductions

At the risk of sounding rather arrogant, I find myself getting more and more frustrated by people justifying their position on the basis of a flawed understanding of the scientific evidence. One that seems particularly prevalent at the moment is the idea that cuts in CO2 emissions will have no effect for many decades. This has been used to argue that we should focus on developing resilience, and that reducing methane emissions is important if we want to stabilise the climate faster.

There are two problems I have with this narrative. Firstly, even if it would take many decades to feel the effects of CO2 emission reductions, that doesn’t mean that we shouldn’t be reducing these emissions now. CO2 accumulates in the atmosphere and how much we eventually warm depends on how much we eventually emit. If we don’t focus on CO2 emissions now, then either we’ll emit more than we otherwise could have (and will have to deal with the additional warming and resulting impacts) or we’ll have to make even more drastic emission cuts in the future. If the impact of these cuts would also not be felt for many decades, why would drastic emissions cuts in the future be more justified than doing so now?

The second problem I have is that it’s not actually correct. Recent work has demonstrated that peak warming from a pulse of CO2 emission occurs after about a decade. In fact, the paper that illustrates this, explicitly discusses the misconception that it would take many decades. So, if peak warming from a pulse of CO2 emission would take about a decade, the impact of emission cuts would also manifest on a similar timescale. In other words, the effects would be felt relatively quickly.

What’s important to recognise is that how much we warm in future depends mostly on how much we emit in the future. Since CO2 accumulates in the atmosphere, limiting how much we eventually warm depends primarily on limiting how much CO2 we emit. This doesn’t mean that we should not also focus on developing resilience and also aim to reduce emissions of short-lived greenhouse gases (like methane). However, we shouldn’t do so because we think CO2 emission cuts will have no short-term impact. Not only does this ignore that ultimately we need to limit the total amount of CO2 that we emit, it’s also wrong.

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33 Responses to CO2 emission reductions

  1. Chris O'Neill says:

    This is the problem with adverse impacts being caused by the accumulated effect of actions over a long period of time. The impact from one relatively small part of it (one year of emissions for example) is, on its own, not particularly significant.

    It’s like a version of the “tragedy of the commons” situation, one individual action doesn’t make much difference but when they’re all added up together it turns into a tragedy.

  2. Dave_Geologist says:

    That’s a cousin of the papers that demonstrate that say going overnight to net zero would pretty much stop temperatures where they are today. Often confused/conflated with stabilising CO2 levels, which requires not net zero but a low level of emissions, enough to counteract environmental uptake.

    In both cases the message is that the solution is in put hands in terms of physics, in principle we’re helpless hostages to locked-in warming, but the problems are financial, technological and political.

    Although given the reluctance or inability we’ve seen from some this last year or so to think two weeks or two months ahead, I suspect ten years wouldn’t be “instant” enough for some.

  3. Chris,
    Yes, that is a good way of putting it. Individually, we don’t contribute much (both in terms of emissions, or emission reductions) but collectively we have a big impact. The key thing is to limit our collective emissions.

    Yes, the Ricke and Caldeira paper is indeed a cousin of those that point out that the zero emission commitment is small. As you say, the problem is more societal/political inertia than climate inertia.

  4. I have no problem with doing three things at once: reducing CO2 emissions, reducing methane emissions and working on resilience. I think the heat buildup we have already developed and the impact of that heat justify taking the problem seriously and engaging in all of the actions that we can take to ease current suffering and to prevent future misery and suffering. I don’t see much progress toward a net zero condition when I look at the CO2 and CO2e emissions records. I think we are currently proceeding to add about 2.4 ppm of CO2 to the atmosphere as the decadal baseline average and that is a very large number given our current situation and a review of the decadal baseline emission levels. We should cut CO2 and CO2e emissions now and see how fast we can hit a net zero condition. Net zero by 2050 is going to cook a lot of living things on the planet. For info on that situation, review the news stories about the coastal creatures that died during the recent “heat dome” episode.



  5. Magma says:

    I suspect a big part of this is the (probably correct*) concept of climatic tipping points, or the fact that permafrost regions and major ice sheets take time to respond to step changes in mean surface air temperatures.

    But as the rule goes, “If you find yourself in a hole, stop digging.” It would be advisable to keep hammering that simple message home.

    * Paleoclimate suggests that we are in a climatically sensitive situation in the Quaternary, with a glaciated continent at one pole and a restricted ocean basin at the other, and cycling between glacial and interglacial episodes with relatively minor forcing from Northern Hemisphere insolation. Maybe other readers have a better idea than I how stable this bistability is likely to be with a doubling of greenhouse gases.

  6. Magma,
    Tipping points do clearly respond on much longer timescales. However, this would still suggest that we should avoid crossing them, rather than regarding these longer timescales as a reason to focus on other response (not that we shouldn’t focus on other factors too, but not at the expense of CO2 emission reductions).

  7. Dave_Geologist says:

    I garbled that sentence but it looks like folks understood anyway. Corrected:

    the solution is in our hands in terms of physics, in principle we’re not helpless hostages to locked-in warming

  8. Greg Robie says:

    This post is predicated on a “rightness” that ignores (does not/cannot model) tipping points. It is anthropocentic in its framing (does not explicitly nuance its assertions relative to change dynamics in the non-anthropogenic forcings of the carbon cycle (relative to tipping points). It’s a [continued] assertion, as established fact, the 10 year peak warming thing (without ALSO acknowledging that this is true based on modeling that sets aside the cryosphere.

    That this relative “truth” is in SR15 does not make that IPCC report the same as peer reviewed published literature. That science, and in SR15, has suffered a political process. The Ricke/Caldeira work included in SR15 assumes Solomon’s, which does not factor in the latent heat of ice that still is in the cryosphere. Is this a nobody is right when everybody is right thing?

    The conclusion reached in this post is a point-well-taken, and this, in my opinion, either way. But couldn’t it be made in a more inclusive way and possibly effect a shift in what is experienced as an argumentative dynamic?

    In the short term future, and/or until the cryosphere is gone, the argument seems to me to be a case of “nobody’s right if everybody’s wrong”.


    sNAILmALEnotHAIL …but pace’n myself

    life is for learning so all my failures must mean that I’m wicked smart


  9. Ben McMillan says:

    I’m kind of thinking it would be useful to have a variety of sources on food emissions stuff: there seem to be a continual stream of papers from folk from the agriculture sector in NZ (and Lynch) that probably don’t cover the full range of opinion.


  10. While I agree with all this technically, I do want to (again) make a (subtle?) practical distinction, which I think will eventually pertain to public policy and perceptions.

    There is a difference between the concepts of:

    the idea that cuts in CO₂ emissions will have no effect for many decades


    even if it would take many decades to feel the effects of CO₂ emission reductions

    Even though the science is clear that reducing CO₂ emissions *does* have a near-term effect on temperatures, it is *also* the case that it will likely take a decade+ to meaningfully *feel* (or detect, perceive, etc.) such an effect.

    If we accept that the transient temperature response is roughly linear with cumulative CO₂ emissions, then it is very difficult to detect significant temperature change attributable to CO₂ reductions for quite some time.

    If we were to reduce emissions by 50% by end-2030 relative to mid-2021, vs staying at mid-2021 rates (approximately 42 GtCO₂/yr), our *cumulative* emissions to end-2030 would grow from ~ 2415 GtCO₂ to 2714 GtCO₂ instead of growing to 2814 GtCO₂.

    Even though we’d have successfully radically reduced emissions for a decade, the ~3.5% cumulative emissions/temperature change difference is not at the level of detectability – either by the public nor, as I understand it, at a significance level that we’d be able to definitely be able to say “we’ve detected the signal”.

    Again, if you assume a TCRE of ~0.44°C / 1,000 GtCO₂, the delta between the 50% emissions cuts by 2030 and BAU of a cumulative 100 GtCO₂ suggests a temperature differential of 0.04°C. Which, yes, when we only have 0.25°-0.75°C left to Paris, is a big deal, but 0.04°C isn’t large enough to overcome the natural variability that we’d have (especially comparing against a counterfactual case that did not materialize).

    And just as the temperature response is prone to pauses due to internal variability, there is a significant chance that we could see a rate of temperature change *higher* under future reduced emissions versus what we’ve experienced, just based on chance and a short enough (but still ~decadal) sample.

    Similarly, the increase in cumulative emissions (and associated temperature increase) in the next decade – ~300-400 GtCO₂ – swamps the difference of ~100 GtCO₂ between the two scenarios.

    We will be trying to tease out a *counterfactual difference* of, say, 0.04°C in a world that has in the meantime warmed by an *observed*, say, 0.13-0.18°C.

    None of this is to say no actual effect, nor the criticality of making urgent reductions (largely because of the same “stock pollutant” issues making the detectable changes small!)!

    But the public is weaned on quick-fix diets and the like of immediate gratification and payback. And it’s a delicate balance between communicating that, yes, it is up to us and our efforts today will make a difference in the next few decades (importantly, in the lifetime of most of those making the changes!), but also setting expectations as to what differences can be expected and by when.

    I know that Marotzke and others have been mooting this “public expectations” and “detection” issue in the scientific literature. Glen Peters and Pierre Friedlingstein discussed on twitter recently as well. I think the take was that at about the level of a decade is when we’d first be able to (statistically) *detect* a difference (if the emissions changes were large enough).

  11. Agree the argument is bad. The conclusion may be fine. (Except for the not caring about CO2 part.)

    The focus was on reducing CO2 emissions because CO2 remains a problem for millennia and CH4 emissions are mostly gone in a few decades. As we are getting closer to the point of zero CO2 emissions we have to start working on also getting CH4 emissions down.

    And adaptations become more and more important, especially in countries that already have bad infrastructure and dysfunctional governments.

  12. If CO2 emission reductions happen and methane emissions continue to rise, we would still experience the heat increase from the more potent, more short-lived greenhouse gas. If we are trying create emission reductions that the public will experience, then we would want to do both.

    EDF says about 25% of current heat is created by our methane emissions and that most of that heat production would be gone in about 20 years if we stopped methane emissions. If you have lived through the recent heat waves around the globe, this sound good. If you have watched wildfires go from lightning strikes to large, uncontained fires on parched, overheated land, this sounds good.

    The US (for example) needs to mobilize to fight global warming they way it mobilized to fight during WWII. We did not fight the Germans and put off a fight against Japan. We fought a global battle against fascist aggression on multiple fronts, multiple “enemies” and we also did fundamental scientific research on weapons that would help us win the war.

    Our global struggle against global warming requires the same mobilization and commitment. The urgency of this fight is apparent to many folks who have endured extreme events, maybe not quite as much to folks who have ridden out the global heatwaves and extreme events in relative comfort or at a safe distance.

    I think we should be stop and think more if we find ourselves with too much focus on any single part of our predicament. I see some folks who fix on one aspect or another and it looks a bit like a dog with a bone.


  13. Rust,
    Yes, I agree that the difference may be small given that the range of possible emission pathways over the next decade or so will probably also be small. It’s also the case that we won’t actually detect the difference because we won’t actually have another world in which emissions were higher against which we can compare. As Victor highlights, we should probably be reducing CO2 emissions because CO2 will remain in the atmosphere for millenia and the less we emit, the less long-term warming we will experience.

  14. Ben,
    Yes, I’m aware of some of the work coming out of NZ and also the paper by Lynch et al. I think I wrote about the Lynch et al. paper in this post. I mostly agree with what they’re highlighting. Were you thinking of some alternative arguments?

  15. Ben McMillan says:

    ATTP: the article linked at the top of the article (Barnsley et. al.) and that leads to the headline figure given is also a NZ people and Lynch affair. They seem to be very prominent in articles downplaying the importance of methane and dietary choices.

    (Also, MDPI is indeed a Swiss-based publisher, and that sounds good, but why is my inbox crammed with invitations to write an article for them?)

    I guess I’m thinking there are lots of other papers that that make the opposite case, that dietary choices can make a significant difference to personal emissions. If you look at the supplementary info in Barnsley et. al., cutting out meat makes a surprisingly big difference if you use typical global emissions factors (and not NZ-specific ones).

    But I think the contentious thing here is really agriculture and food, rather than methane. If it were some other sector emitting all the methane people would be a lot happier with ‘just stop emitting all the greenhouse gases ASAP’.

  16. Ben,
    Thanks. Yes, I agree with you about MDPI. Odd place to submit a paper if you think it would be suitable for a more reputable journal. I largely agree with what was presented in the Lynch et al. paper which was suggesting that we should be cautious of focussing on agricultural emissions at the expense of CO2 emissions. However, I don’t have any sense of whether or not the argument in the Barnsley et al. paper is reasonable. It may be that switching diets won’t have much impact on lifetime emissions, but this doesn’t necessarily seem obvious, to me at least.

  17. Willard says:

    > why is my inbox crammed with invitations to write an article for them

    You should write for AT’s instead, that’s for sure!

  18. I think some tipping points respond on long timeframes and others may be more like rather abrupt changes in state.

    “Most of the emissions are caused by fires, many deliberately set to clear land for beef and soy production. But even without fires, hotter temperatures and droughts mean the south-eastern Amazon has become a source of CO2, rather than a sink.”

    I think the smart move is to grab all the “low hanging fruit” on all ghg emissions as fast as possible, and work upward from there in terms of reducing emissions. Temps alone already creating climate complications, feedbacks and great suffering for some.


  19. Ben McMillan says:

    Rather than me critiquing Barnsley et. al., maybe it is more sensible just to look elsewhere

    They find that choice of diet is a big deal in terms of emissions/climate (and not just in the short term). I think that might actually be the prevailing view, rather than “it only makes a tiny difference”.

    That seems to be how I read the literature survey in IPCC Special Report: Special Report on Climate Change and Land, sec 5.5.2 Demand-side mitigation options:

  20. Ben,
    It might depend on how they’ve compared methane and CO2 emissions. If they’re using GWP, rather GWP*, then that would over-estimate the impact of methane emission reductions, relative to CO2 emission increases.

  21. Ben McMillan says:

    The paper I cited is just using a full IAM. And seems to be in line with most of the other literature in this area, going by the IPCC report.

    I think the difference is more in how the scenario is set up, how data is presented, which outcomes are highlighted, and NZ emissions factors being quite unusual (land use is thorny as usual).

    Using GWP* and looking at a time point 20 years after the person dies indeed gives you the result you expect (methane has no effect).

    (I wonder whether you really want a full IAM rather than GWP* to deal with agriculture anyway, given that land use emissions have complicated time-evolution).

  22. Ben,
    Yes, I agree that how the scenario is set up can quite strongly influence the outcome. You’re right, that a full IAM, or something that properly models the time evolution, may well be better than simply using GWP*. However, I do think that GWP* does a reasonable job of estimating the time evolution of the impact of the various GHG species.

  23. Ben McMillan says:

    ATTP: Yep, I agree that GWP* is useful for getting the time-dependence roughly right.

    On a related note, DICE is really bad at modelling Paris-compliant scenarios, partly because their climate model is linearised around 3.5C. So for anything other than ‘quick-and-dirty’, a proper IAM is needed.

  24. Ben,
    Yes, I saw that. I find it bizarre that DICE 2016 R2 would have suggested that the carbon budget for 2C was 460 GtCO2, since this would have seemed obviously too low to anyone who was aware of the carbon budget estimates.

  25. Ben McMillan says:

    Given the author lists on his papers, maybe Nordhaus doesn’t interact much with climate people.

    Willard: I probably engage too much as it is and get too excited… which is the reason I don’t do anything on twitter other than lurk.

  26. Willard says:

    It was more a question than a comment, Ben:

    When will you write a guest poast?

  27. Steven Mosher says:

    a different type of feedback and tipping point

    The amount of 에너지 that California’s grid would lose if Edward Hyatt goes offline is only a sliver of its total peak demand (44,000 MW), but the state has been increasing its reliance on fossil fuels to make up for any lost power as the grid faces strain. Last week, Gov. Gavin Newsom lifted environmental restrictions on natural gas-fired power plants in a move to expand the state’s 에너지 capacity. In the same 경영진 order, he called on Californians to reduce their energy use from peak hours (4 to 9 p.m.) to lower 위험 of rolling blackouts.

    Mohit Chhabra, senior scientist in the Natural Resources Defense Council’s Climate and Clean Energy Program, notes that the state’s grid should be able to handle a possible shutdown at the Hyatt plant. But withstanding future 기후 disasters will require a resilient grid, one that 고객들 can depend upon without sacrificing their energy use.

    “Vulnerable Californians need (새로운 용도,상황에) 맞추다 to 기후 change too,” Chhabra told Motherboard in 이메일. “For this they need efficient 집들 and appliances.”

    The plant’s shutdown represents a new, terrifying development in the feedback loop between climate change and grid resilience: Rising temperatures demand increased reliance on air conditioning and other cooling mechanisms, the energy use for which further contributes to climate change, and so on. In some parts of the country, like Texas, local electrical grids have proven unprepared to handle this strain. But the loss of hydropower, a renewable energy source, in response to extreme weather events like drought, is cause for concern.

  28. Steven Mosher says:

    sorry about the korean. i use toucan.

  29. Eli Rabett says:

    Basically the same arguments made against the Montreal Protocols with a lot of confusion thrown in.

    Stabilizing emissions is terrible policy, stabilizing concentrations is bad policy. The only thing that works is eliminating emissions, and in that case there is a rapid drawdown over 1-2 centuries driven by equilibration into the deep ocean, followed by the millenia long slow process of incorporating the excess remaining into the lithosphere.

    Sadly, the rapid process does not help all that much with surface temperatures as the excess heat driven into the oceans emerges.

  30. “Sadly, the rapid process does not help all that much with surface temperatures as the excess heat driven into the oceans emerges.”

    I think Eli is correct. Folks like to talk about how warming would stop quickly once we reach a net zero status. Quickly is usually defined as a decade or two. Maybe that is the time period that we would expect heat from oceans to emerge? Or maybe that heat cycle and other carbon cycle changes, like ice/glacier loss, albedo change, permafrost thaw, etc. are not getting the considerations they deserve?

    Either way, the CO2 and CO2e record does not suggest that are on a patch to stable emissions, net zero emissions or zero emissions state. In fact the accumulation of ghg in atmosphere and oceans indicate we are still on a path to increased and record emission levels:

    In the face of these bleak numbers, it is a challenge to layout rosy scenarios, but I think we should continue to look for means to reduce emissions, slow warming and make the changes that we need to change our trajectory. In the case of reducing warming on the short time frame that our species likes, the low hanging fruit is methane and the other ghg that produce more global warming than CO2. That probably sounds good to the folks who have spent some days under the heat dome this year. There is no reason that we would have to neglect CO2 emission reductions in order to pick the low hanging fruit. I think our species’ response to global warming requires a global response, a shift to a “war-time” footing where all other considerations are given less weight. Imagine a shift of most of the global military spending into global warming mitigation and reduction. Imagine that. I am a dreamer.

    And that dream is a hard sell to the deciders, who are dreaming of heading into space or colonizing Mars. Weather report? Hard rain’s gonna fall.



  31. mrkenfabian says:

    Mike, I think the Grand Space Dreamers are a tiny subset of the ultra-wealthy. Barring a few well publicised exceptions their wealth is their primary protection. Beyond that, bunkers, not Mars or space colonies, are their fallback.

  32. Russell says:

    “, bunkers, not Mars or space colonies, are their fallback.”

    What time does the next asteroid stop at The Clock of The Long Year?

  33. mrkenfabian says:

    Russel, I’m not familiar with The Clock of the Long Year.

    Most of the catastrophes being faced or prepped for are well short of total planetary destruction and Chicxulub scale asteroids are 1 in 10’s of millions of years events. More risk of smaller but still major impacts but which would have global impacts for an interconnected global economy. I think we are still talking 1 in 100,000 years events for big regional catastrophes, versus an unknowable but surely a much greater and more imminent risk of societal collapses from the mismanaging of the climate/emissions/energy problem descending into blameshifting, global conflict and war – within the coming century.

    I suggest that to survive independently of Earth in space requires an advanced, industrial economy in space of scale and capabilities equal or exceeding the largest nations on Earth. A healthy, wealthy Earth economy is the essential ingredient for all space ambitions – which I think should include long term meteor defense for Earth, with higher priority than Mars or other colonies. Which I think need to be emergent outcomes of “natural” growth of economically viable activities, not colonies as an objective.

    Even big military bunkers are for preserving the ability to defend their nation, not Dr Strangelove scenarios.

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