Approximate net zero

Since I have a few free moments, I thought I would briefly highlight a paper by Jenkins et al. on [t]he Multi-Decadal Response to Net Zero CO2 Emissions and Implications for Emissions Policy. Recent IPCC reports have highlighted that limiting human-caused warming will require getting human emissions to (net) zero. What this paper suggests is that it might be better to aim for approximately net zero.

The analysis in the paper suggests that positive emissions of 2.2GtCO2/yr might be consistent with halting anthropgenic warming on multi-decadal timescales. The 95% range, though, is from -7.3GtCO2/yr to +6.2GtCO2/yr, so it could be higher, or it could require net-negative emissions. As far as I can see, this is broadly consistent with earlier work on the zero emission commitment, which suggested that the best estimate was that zero emissions would stabilise human-caused warming, but that it could also lead to some continued warming, or some cooling.

Personally, I quite like the suggestion of thinking in terms of approximate net zero. If we can reduce human emissions by ~90% (which is what would be required to get to ~2.2GtCO2/yr) then even if it doesn’t quite stabilise human-caused warming, it should significantly reduce the rate of warming. It woiuld give us some time to work out if emissions need to be reduced further, and if we would need to implement significant amounts of negative emissions.

Of course, it’s still not going to be easy to reduce emissions by ~90%, which is another reason why I quite like the idea of thinking in terms of approximate net zero; let’s try and get close before worrying about whether or not it has to be exactly zero, or negative.

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42 Responses to Approximate net zero

  1. dikranmarsupial says:

    I like the approximate target as well – it highlights that there isn’t a step change in impacts at net zero, which might disincentivize people when we realise that we won’t meet the target (and we won’t). 90% of the way to net zero would still be an achievement and would realise most of the benefits.

  2. The idea of net zero is like the idea of a vacuum. These ideas are inherently squishy. There is no there there for a variety of reasons. From the paper: “The IPCC’s sixth assessment report (Masson-Delmotte et al., 2021) made a much stronger statement: “from a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions,” and more specifically, “achieving global net zero CO2 emissions, …, is a requirement for stabilizing CO2-induced global surface temperature increase” (emphasis has been added where language differs from SR1.5). AR6 implies that net zero CO2 emissions is a necessary condition to stabilize warming, while SR1.5 instead argues that net zero and declining net non-CO2 RF is sufficient to halt warming on interdecadal timescales. This distinction is important: while both reports emphasize that halting warming requires at least an order of magnitude reduction in CO2 emissions, SR1.5 leaves open the possibility that stabilizing warming may not require strictly net zero CO2 emissions.”

    I guess hippies need punching and the hippies appear to have taken over with AR6 and are talking about the “requirement” to get all the way down to some fine point called net zero, when something less than net zero might be a sufficient target.

    For me, net zero has sufficient squishiness as a target to make the difference between requiring achievement of net zero status and achieving something pretty close to net zero status a semantic distinction. I think it would be easier if we just requiring the species to limit emissions to a net zero-ish condition.

    I understand the concern that overstating the problems of global warming might cause people to lose hope and give up on emission reductions. I believe there is no doubt that such a thing might be true. I think this paper is helping us by pointing out the error of requiring a true and exact net zero status is an overreach and could create a backlash against an all-powerful global climate bureaucracy that might arise and attempt to enforce requirements that could endanger our freedoms and our very way of life. I believe that there is no doubt that such a thing could happen.

    This paper has put me in a wobble. Are the authors punching hippies? or are they helping us prevent the rise of a global climate fascism that would force us to overshoot with our response to global warming?

    Aren’t we already sufficiently on our way to stabilizing global temp rise in this century or perhaps early next century? Our global CO2 count was 420.99 ppm in June and now it’s down to 417.51 ppm for November. I haven’t finished all my calculations yet, but that’s a large drop in a short time. If you plot those numbers and extrapolate, it’s pretty easy to see that an ice age is a possibility. I am not saying the ice age is likely, but we should be careful about blowing beyond a sufficient CO2 reduction, something net zero-ish, by requirements that we hit some magical time and place that we define as net zero.

    This seems like a great way to roll out the new year.



  3. small,

    Our global CO2 count was 420.99 ppm in June and now it’s down to 417.51 ppm for November. I haven’t finished all my calculations yet, but that’s a large drop in a short time.

    This is just the annual atmospheric CO2 cycle. It peaks in about May and has a minimum about 5 months later. The amplitude is 5 – 6 ppm. This doesn’t mean that there isn’t a long-term increase that is being driven by human emissions.

  4. Steven Mosher says:

    net zero reminds me of covid zero. how’d that work?

    beware of setting inflexible targets even when you have absolute power.

  5. Steven,
    Maybe some similarities, but what seems pretty clear is that human emissions will have to get pretty close to zero to stabilise global surface warming and that if we don’t manage to do so global warming will continue and the impacts will probably become increasingly severe.

  6. dikranmarsupial says:

    Could have net negative CO2 but not net negative COVID.

    I would defer to real experts though, such as Stewart Agnew MEP



    We are currently at ~40 GtCO2 or ~10GtC so (40 – 2.2) /40 = 94.5% reduction not 90% reduction.

    Or maybe 3.664*10.13 = 37.1 * 0.1 = 3.71 not 2.2

    Also, everything suggests we have not peaked yet, so instead of 90% it is much more likely to be 95% or even higher. :/

    At lease they do agree with me though, as in, not zero by 2050! 😀

  8. Scientists thought carbon emissions had peaked. They’ve never been higher.

    “According to a report released last month by the Global Carbon Project, carbon emissions from fossil fuels in 2022 are expected to reach 37.5 billion tons (Gt) of carbon dioxide, the highest ever recorded.”

    Walking the walk is definitely not talking the talk. I am not a doomer or even a realist, but seriously, what happens happens. And that is just the CO2 budget, so that we are not even total GHG emissions.

  9. EFS,
    Yes, it is more like 95%, than 90%. I was approximating 🙂

    Indeed, we’ll first need to actually peak emissions before they start coming down, and we seem to be struggling to do that.

  10. Okay, you’ve set a goal. Shall we steer the conversation towards mechanisms?

    I would suggest that a good second step (we’ve certainly started on the first) is to set a carbon tax in developed countries, with tariffs to encourager les autres and negative tariffs to help the developing world.

    I mean, markets don’t solve everything, but to ignore a market-based contribution to the solution of a problem like this really seems like wasting an opportunity.

  11. Tom,
    I don’t disagree with that. My understanding, though, is that in many developed countries there is little political will to actually impose a carbon tax.

  12. …hence the tariffs.

  13. E.G., the EU institutes a carbon tax at $20 / tonne. The U.S. does not. The EU adds a noncompliance tariffs to goods exported to the EU from the U.S. It notably applies a negative tariff to goods from ‘good effort’ developing countries using the money it squeezed from the U.S.

  14. Yes, but how do you actually get that implemented? I agree that a region that wants to impose a carbon tax can account for imports that don’t using a tariff, but it still requires the political will to actually do that.

  15. I kinda think the political will does exist in the EU, at least at top levels of government. If NGOs and other interested parties pushed (hey! Maybe climate bloggers, too!) it could happen.

  16. It might do a bit better than throwing tomato sauce at old paintings, anyways.

  17. It might do a bit better than throwing tomato sauce at old paintings, anyways.

    Sure, I don’t think the options are “impose a carbon tax and introduce trade levies to compensate for regions that don’t do so” and “throw tomato sauce at old paintings” 😉

  18. What? You mean there are more than two options? OMG…

  19. dikranmarsupial says:

    ” at least at top levels of government. ”

    unfortunately if they think it will loose them the next election, they won’t do it. This isn’t an “Iron Law” though, just a problem with democracy. The thing we really need is the political will in the electorate. However, we are too busy discussing science/economics/implementations rather than discussing our values and what we want to see happen.

  20. dikran says “… we are too busy discussing science/economics/implementations rather than discussing our values and what we want to see happen.”

    Mike says: Amen, brother. So right. This is exactly what we should be discussing. The formula might be our values, what we want to see happen, how we would implement/plan/develop to achieve what we want to see happen in a manner that is consistent with our values.

    I would suggest that studying and spending a lot of time on a discussion of whether we should require an achievement of some rather nebulous goal like net zero in a time frame that is even more nebulous or whether we should instead engage in a discussion of a kinder/gentler achievement of an approximate net zero condition in a nebulous time frame might fall in to the category of staying busy discussing science and neglecting a discussion firmly grounded in values and a vision of what we want to see happen.

    Endless wrangling will no doubt ensue, but I will give a solid “two thumbs up” to the idea of values discussion and what we want to see happen as the primary focus area. Implementation and timing should follow that discussion. Economics has to earn a place at the table and on the agenda because as Bucky Fuller notes, we can afford to do anything that we have to do. What are our values? What do we want to see happen? How and how fast can we make that happen?

    What do we want? Achievement of an approximation of net zero!! When do we want it? Now!! or maybe 2040? Is 2030 a possibility?

    We are already observing a drop of 3 ppm in just the past six months. That is a real drop. How much of that do we have to give back in the next 6 months? (one of my values is whimsy)



  21. In the developed country where I live there is little political will for any taxes. I think this happened because the right wing political parties spent a lot of time talking about their values and what they wanted to see happen. One of their mostly closely held values is that the accumulation of individual wealth is a good thing and that any form of tax erodes a god-given right to accumulate wealth. It is quite easy to jump from that value statement to the idea that any form a tax is a bad thing.

    That leads us back to dikran’s suggestion that we should focus on a statement of our values and a vision of what we want to see happen in the future.

    I like the idea of a steep progressive tax system with a top rate that is essentially confiscatory. I like this idea because I think it a better thing to have good public schools than it is to get to observe billionaires shoot themselves into space and return to the earth to accumulate wealth for their next adventure.



  22. off topic, but:
    Headline says “Australia flood crisis: ‘Once in a century'”

    I think that is misleading. It may be true that this flooding is the worst that has been recorded in the past 100 years, but to label it as “once in a century” flooding event effectively buries a more honest and useful headline that would identify the risks of heavy flooding on a warmed and warming planet.

    Nits need to get picked, I guess. Lot of flood water anyway you cover it. I think there is also some heavy flooding happening south of me in Northern California right now. Different storm system, I think.

    To align with Jenkins et al., I would suggest changing to Australia flood crisis: “Once in approximately a century.” Or “Maybe once in a century flooding.”


  23. I have lost count of the number of times that I have been told that emissions have peaked and we only need to wait for the data to be gathered to show that such is the case. This has usually been expressed to me when I have posted my personal distress about the numbers and my sense that perhaps the numbers are continuing to go the wrong way.

    I think I have learned a valuable lesson from this experience and I now express a more positive message. It is certainly possible that emissions actually peaked yesterday afternoon and have now begun a steady decline that will soothe our fevered brows and secure a stable climate for our grandchildren. I hope that is true. It is most certainly true that our accumulation level in the atmosphere has fallen approximately 4 ppm in just the past six months. Despite the naysayers, I have not given up hope that we have now turned things around. I hope and pray that we will not be giving back all of the decline in CO2 accumulation of the past six months. Such a thing is not impossible.


  24. Small,
    I’ve already pointed out that the variation over the last few months is simply part of the annual cycle. Why not check what atmospheric CO2 was at this time last year and compare it with what it is now?

  25. russellseitz says:

    Small, sqiushy concepts have their uses,

    When will atmospheric CO2 capture proposals escalate to simply capturing the atmosphere at large. Were 10% or so stored away as compressed air, the resulting barometric drop would cool the globe by effectively moving everything uphill a thousand meters.

    Fossil fuel flacks should rush to applaud the concept as it would both reduce the infrared optical depth and open vast marketing opportunities for diesel compressor fuel.

  26. dikranmarsupial says:

    “Why not check what atmospheric CO2 was at this time last year and compare it with what it is now?”

    indeed, or look at a CO2 time-series from the southern hemisphere, which has a much weaker seasonal variation (because it is mostly caused by changes in vegetation, and most of the land mass is in the northern hemisphere)

  27. Chubbs says:

    Guessing that our best level of stabilized long-term emissions depends on the emissionpathway. The faster we reduce emissions the more likely we can have some room for limited long-term emissions. Unfortunately the path we are on will limit our future options.

  28. Eventual_Horizon says:

    I’d love to read an informed opinion on Hansen’s new paper “Global Warming in the Pipeline” which asserts that our current levels of GHG are effectively already at a doubling of CO2. From the paper: “Eventual global warming due to today’s GHG forcing alone — after slow feedbacks operate — is about 10°C.” A rather shocking claim and quite at odds with the notion that everything will more or less even out if we reach (approximately) net-zero.

  29. because it’s not as encouraging as looking back on past six months. Lighten up and enjoy this moment when we are again well under 420 ppm. A day could come when we don’t see a monthly average number under 420 ppm and you will have missed this opportunity to celebrate.

    If you want to go all dark and gloomy or worry about proper context, take a long look at the Hansen article that EH mentioned:

    I stand by my statement, we have had a dramatic drop in CO2 levels in the past six months. The statement is most certainly true. We don’t have to give all those gains back in the next six months. How much of this good news can we find a way to retain? Taking potshots at the statement is like complaining about spring flowers, Oh, so what? They never last. Look again in six months and you can’t find a single one. Dry some flowers in a book if you want to see them and smell them again in a couple months. Live a little.

    Had a friend who sang for a band. She is very pretty but didn’t get all girly-sexy generally and wasn’t inclined to do it for the gig. Old piano player finally convinced here when he leaned over to her one time and said, hey, would it kill you to wear a little mascara. She bought some mascara for him, wore it for him and he was a happy old dude. Audience seemed to get up and dance more. He was right that it was a crowd pleaser and nobody died. Single tube of mascara can go a long way if you use it 4 to 8 nights a month. Bat your eyes and shake a little bit. Give them a show. What’s the harm?


  30. Eventual,
    I was thinking about that. If I get some time, I’ll have a look at it and try and write something.

  31. Eli Rabett says:

    Set limits. There are clever people out there who will show you how to meet them. That’s the lesson of the Montreal Protocols.

  32. dikranmarsupial says:

    “I stand by my statement, we have had a dramatic drop in CO2 levels in the past six months.”

    we have had a dramatic drop in temperature in the past six months. It is called “Winter”.

    It isn’t a good idea to stand by statements that while technically true are deeply misleading – especially when it has been explained why they are misleading. We get enough of that from politicians.

  33. lerpo says:

    EU has announced the world’s first tax on the carbon content of imported goods.

    “This new precedent will likely force industry leaders and policymakers to talk about establishing a carbon price in the U.S. — even if they’re against it”

  34. Magma says:

    dikranmarsupial: “This isn’t an “Iron Law” though, just a problem with democracy. The thing we really need is the political will in the electorate.”

    This shows the evil genius of the strategies adopted by fossil fuel companies in the 1980s: deny, obscure, confuse, dismiss, lie, and rent or purchase key blocks of politicians and a handful of contrarian scientists (who didn’t need to be particularly competent). While its precursors were the campaigns to dismiss the provable health risks of leaded gasoline and tobacco, climate change denial took things to another level entirely. Without hyperbole, I think these actions amount to both corporate fraud (at the lower level) and crimes against humanity (at the higher one).

  35. Willard says:

    The only Iron Law is Very Tall’s:

    I do notice that ATTP’s doesn’t even come up in a google search. Maybe because its become irrelevant. Now that Ken has become a modicum of moderation and politeness, he is attracting less negative attention. But that’s a good thing. Maybe he can make some contributions to science.

    It’s as if troglodytes realized out of a sudden how algorithm polarization worked. Perhaps one day they’ll realize how one’s search history influences what one gets.

    I have no problem finding AT’s in my search.

  36. Pingback: Hansen’s 10C | …and Then There's Physics

  37. Magma says:

    The irony of that comment appearing on JC’s blog could only be surpassed by posting it on WUWT, assuming it’s still around. The various grammatical, spelling and punctuation errors are nice touches, though I wouldn’t have thought VTG needed to display his tribal membership that way.

    Off-topic, has the deep problem of whether “most” and “more than half” and “>50%” are equivalent finally been solved?

  38. Willard says:


    The comment is from David Young from The Boeing Company.

    Very Tall’s Iron Law is simply – Blogs have the commenters they deserve.

    Sorry if I was unclear.

  39. Magma says:

    I should have checked rather than assumed, but I’m trying to limit my visits to such websites.

  40. Magma says:

    addendum: I also mixed up VTG with Tallbloke, so apologies to the first should he happen to read this

  41. Steven Mosher says:

    Maybe some similarities, but what seems pretty clear is that human emissions will have to get pretty close to zero to stabilise global surface warming and that if we don’t manage to do so global warming will continue and the impacts will probably become increasingly severe.

    my point was this. the chinese set a goal of zero…. clearly impossible..

    that then committed them to try everything. xtreme cures.

    cures worse than the disease.

    and this of course led to unforeseen consequences: riots in china.

    you have to set acheivable goals and show results

    hint if you weld people into their apartments and

    A: the disease still spreads and
    B: some people die uneccisarily

    thats a badd bad thing

    so what ever you do on climate
    if you impose measures
    A: warming better stop
    B: disasters should stop.


  42. About half way through watching “The Carbon Cycle Behind Net Zero” (Gresham lecture by Myles Allen) and seemed worth recommending already…

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