RCP8.5 and net-zero

There’s a narrative that seems to be developing that suggests that the requirement to reach (net) zero emissions is largely based on the high-emission RCP8.5 scenario. Since this is (according to some) no longer plausible, we should give up on our (net) zero plans, because they’re no longer necessary and will do more harm than good.

One obvious problem with this isn’t that there isn’t some boundary beyond which catastrophe ensues, and below which everything is fine. We expect the impacts to become increasingly severe as warming continues. Just because we’re unlikely to follow an RCP8.5-like pathway doesn’t mean that there won’t be severe impacts. If anything, there are already regions, and communities, that are being impacted by climate change and the difficulty of reliably estimating the impacts means that we may well be under-estimating the impacts of even the lower levels of warming.

Another issue is that there is a complex relationship between emissions, concentrations, and warming. This means that even if we don’t follow an RCP8.5 pathway, we still can’t rule out that we’ll experience levels of warming typically associated with RCP8.5 (> 4C, for example). Hence, ruling out an RCP8.5 pathway doesn’t immediately rule out RCP8.5-like impacts.

Finally, there is an element of irony to this narrative. One of the reasons why RCP8.5 has become much less likely is because of the progress that has already been made and the expectation that the promised climate policies will be implemented, and strengthened. Essentially, there’s an expectation that emissions will soon peak and start to decline. So, in some sense, the reason why RCP8.5 is much less likely than it once was is largely because we now think that we’re on a pathway towards (net) zero.

So, to suggest that the implausibility of RCP8.5 means we can give up on current climate policies is essentially arguing for a pathway that makes RCP8.5 more likely. To be clear, it’s always been a worst-case scenario, rather than being a pathway we were likely to follow. However, that’s mostly because it was unlikely that we would simply not develop, and implement, alternatives that would reduce emissions, not because it was absolutely impossible to follow an RCP8.5-like pathway.

This entry was posted in Climate change, Global warming, Policy and tagged , . Bookmark the permalink.

30 Responses to RCP8.5 and net-zero

  1. A couple of extra comments. For those who recall the lengthy RCP8.5 debate of 2019, we should probably (sarcastically) thank Roger, Michael and others for developing a narrative that is now being used to argue against net-zero. Somewhat ironic given that one of the (supposed) motivations for their narrative was them claiming that too much focus on RCP8.5 was undermining arguments for climate policy.

    Also, I realise that we could follow a pathway that neither reaches RCP8.5 nor (net) zero by 2100. However, if the emissions are still reasonably high it would eventually lead to an RCP8.5 level of forcing and if they were low enough to not reach RCP8.5 for a very long time, then it would probably – in many respect – be largely indistinguishable from (net) zero.

  2. Bob Loblaw says:

    Been there, done that, and have the T-shirt. Y2K was not a catastrophe, so all the effort spent in the 1990s to prevent a Y2K catastrophe was not necessary, and Y2K was never a real problem.

    Or so the story goes….

    You had a parachute when you jumped out of the airplane at 10,000 feet and you landed safely, so if you had not bothered with the parachute, the 10,000-foot fall would not have been a problem anyway. And during the first 9,999 feet of the fall, any evidence of damage was totally lacking. The alarmists telling you “don’t jump without a parachute!” had some other hidden agenda.

  3. jacksmith4tx says:

    Re: Y2K
    And they ignored the danger of unleashing the internet with only a 32bit address. The original architecture assumed IP address would be used to verify the identity of the clients. Once they ran out of PIs it opened the door to anonymous actors, both real and virtual, elusive and malicious. Truth is ephemeral and rich keep getting richer.

  4. Phil says:

    “… we could follow a pathway that neither reaches RCP8.5 nor (net) zero by 2100.”

    This actually seems the most likely to me. Take electric cars, for example. Sure, almost all people will do just fine almost all of the time. But there are places and times were there isn’t the infrastructure and burning fossil fuels will be the best alternative. Sure, a tiny minority, like hauling stuff to the South Pole and similar remote places. Long term, Lithium air batteries or e-fuels might cover this, and sometimes biofuels might cover this, but getting to 100% can be a whole lot harder than getting to 99%.

  5. Phil,
    Sure, but I guess my point was partly that in such a scenario, unless the global economy has collapsed, most of energy infrastructure (and transport) would be from alternative sources, or sources that are not emitting. Hence, this would seem to be pretty similar to the kind of pathway we would be following if we wanted to get to net zero (i.e., focussing on implementing alternative technologies).

    Also, if we do end up in a situation where residual emissions are ~10% of current emissions, then it would seem feasible to look at carbon dioxide removal (CDR) to remove these residual emissions. CDR may not be a viable alternative to emission reductions in most circumstances, but it may well be a viable way of removing those emissions that are difficult to avoid (for the reasons you suggest).

  6. Susan Anderson says:

    There is simply never a time when making things less bad is useless. Harm from climate change, toxic waste, and other forms of waste and excess is a continuum, and efforts to improve and remedy this are an affirmation of life, even when they involve complicated tradeoffs which are far from perfect. Life is a continuum too.

    I can’t believe this needs to be said, it’s so obvious.

  7. We have made so much progress at cutting emissions. We should not worry or even mention stuff like global economy collapse. There is no way that could happen. I have a bunch of dollars in my 401k’s that are propping up the economy in the USA.

    Sure, we can do better. All it takes is a “can do better” mindset. I think if you plot the decrease in our annual emissions it it easy to see that we will reach net zero in no time. Well, almost no time. Stay upbeat. Enjoy the heat. Get some sunscreen on and get a tan!

    How are we doing on CO2? Killing it!

    April CO2
    April 2023 = 422.73 ppm
    April 2022 = 420.02 ppm

    2.71 ppm year on year! This is an amazing number given that our species has not really even set its mind on hitting global emission accumulation reduction so far. Think what we will do once we get serious about emission reduction. Also, if you extrapolate some ideas on carbon capture and DAC, we have basically already hit on the net zero formula. As Captain Picard might say, “Engage.”

    Please, no more talk of collapse. We got this.


  8. Jon Kirwan says:

    … to suggest that the implausibility of RCP8.5 means we can give up on current climate policies is essentially arguing for a pathway that makes RCP8.5 more likely.

    I think the above is the blog’s logline. I’d have led with it.

    I next read Susan’s comment and noted it closely mirrored my thoughts seconds earlier. So nothing more to add.

  9. russellseitz says:

    This post happily coincides with the commercial debut of high energy density lithium batteries designed with aircraft in mind


    At half a kilowatt hour per kilo, they should help kickstart electric trucks and ships as well.

  10. Bob said:

    “The alarmists telling you “don’t jump without a parachute!” had some other hidden agenda.

    Years ago I read an opinion piece that climate change was a smokescreen to avoid confronting the “practical” existential crisis of fossil fuel depletion. Telling the populace that supplies are limited would lead the citizenry to unrest, such as what occurred with the yellow jacket riots in France (caused by a fuel tax). The rationale for climate change mitigation as a goal is that something could be done without impacting their day-to-day lives. I think it was Richard Heinberg that wrote the opinion but not certain, as he later quoted Michael Mann in that “Importantly, fear does not motivate” in terms of maintaining a positive outlook that change is possible without invoking immediate dread. The No Regrets Strategy is another means of mollifying the fear, making it a more encompassing rationale to transitioning off FF.

  11. Mal Adapted says:

    Susan Anderson:

    I can’t believe this needs to be said, it’s so obvious.

    Nonetheless, you said it very well. Thank you.

  12. Chubbs says:

    RDP85 has become unrealistic because clean energy technologies, solar/wind/ev/batteries etc., have outperformed expectations. If they continue to outperform, then the iron law is going to push towards net zero.


  13. clean energy technologies, solar/wind/ ev/batteries etc., have outperformed expectations. If they continue to outperform, then the iron law is going to push towards net zero.

    I’m not sure the exact point you’re trying to make there, but arguably that eventuality could be seen as *vindication* of “the iron law”: as in, we acted substantially on mitigation when, and only when, it became in our strict (project) financial interest to do so.🤷

    I’d have to go back to read “the iron law” originator’s definition of the term, but I don’t think “alternative (low- to zero-carbon) energy sources outcompeting on costs and displacing fossil energy sources” would be a strong refutation?🤷

    Or maybe that was your original point?🤷

  14. rust,
    As far as I can tell, the “iron law” will end up being whatever the originator of the idea decides best fits the narrative they’re trying to promote 😉

  15. I’ll also make another slight detour from the main point of the original blogpost, just to make a brief comment on the exceptionally good Way, et al., 2022 paper linked above, “Empirically grounded technology forecasts and the energy transition”.

    Very encouraging research with big implications for the near-term outlook for renewable energy and the potential large payoffs available by actually accelerating their deployment.

    But what I think escapes a lot of people on that paper is that the main technologies they identify as exhibiting these key characteristics (modularity, etc.), they themselves see them topping out at displacing about 75% of carbon emissions (and I think even 75% of just the “FFI, ex-of land use change emissions, ~35 of current 40 GtCO₂ yr⁻¹” emissions).

    As in, Way, et al., *still* finds a lot of applications that remain hard (expensive) to abate, and where the mitigation technologies being pursued don’t seem to be amenable to the attributes they identify that contribute to rapid learning curve effects.

    That’s not entirely on point in this thread. But it seemed to me that this point got glossed over in the articles, podcasts that greeted the paper last summer(?).

    I saw co-author Matthew Ives make a presentation on the research, and he spent a considerable amount of time towards the end highlighting this remaining. And then bridging from that point to hand over (quite enthusiastically) to the next speaker, their Oxford colleague, Myles Allen, who was talking about the role in this regard for CO₂ removal and geologic storage.🤷

    I’ll see if I can find the slides I had from Matthew Ives’ presentation. But I seem to recall this is also in the paper itself – if you are primed to look for it.

    In that we’re required to get to net zero CO₂ emissions, if something like “the iron law” holds *unless* things get very cheap relative to continuing to combustion fossil carbon, it might have remaining insights.🤷

  16. from the “are we doomed” piece on common dreams: “… the bad news. While we could live perfectly well with less energy, that’s not what the managers of our economy want. They want growth. Our entire economy is structured to require constant, compounded growth of GDP, and for all practical purposes raising the GDP means using more energy. While fringe economists and environmentalists have for years been proposing ways to back away from our growth addiction (for example, by using alternative economic indices such as Gross National Happiness), none of these proposals has been put into widespread effect. As things now stand, if growth falters the economy crashes.”

    Almost six years after this article and the concerns that underlie its publication, we are still enjoying an economy structured around constant growth and the elected leaders from the “climate reality” party in the US continue to talk about the need to reduce our fossil fuel use as they act to open more ground to drilling to get more fossil fuels in the pipeline. It is strange to watch this happen, but it’s good I guess. Our economy continues to grow and produce amazing amounts of wealth that are being directed into the hands of the captains of our industry and economy who know best how to keep the world and our lives running on an even keel.

    I continue to see a lot of homeless people who appear to be unable to figure out how to get engaged in the opportunities that exist all around us. My guess is that these folks have lost hope in our way of life because of drag queens and the woke curriculum that is flooding our society. I continue to keep one eye open and woke, but the other eye is transfixed by the opportunities and bright shiny things that are available and can be delivered right to my doorstep.

    I am thankful that I no longer hold on to the kind of deeply destructive ideas of collapse and destruction that I used to have. This group and its positive attitude about the resilience of our world and our species has been a godsend to me.

    We are doing great. No doom and gloom please. As this common dreams article states, scaring people is not the way to go. Let’s celebrate our achievements!

    Just look at the way we have slammed the door on CO2 in the atmosphere:

    Daily CO2
    May. 21, 2023 = 423.75 ppm
    May. 21, 2022 = 420.42 ppm
    co2.earth source

    We are killing it!



  17. Willard says:


    If there is an iron law of climate policy, it is that when policies focused on economic growth confront policies focused on emissions reductions, it is economic growth that will win out every time. That’s how I introduced the iron law in my book The Climate Fix back in 2010.


    In 2010, that may have sounded cool, almost a truism. People want cheap energy, the cheaper the better. Until they realize that coal creates smoggy cities and oil creates wars, or that very few decides what the price of crude oil will be next week:


    The law might also need some clarification to make sense of our current market conditions. For instance, it’s not impossible to try to do both growth and climate policies, say with the Inflation Reduction Act and the CHIPS Act.

    To create a dichotomy between technology and infrastructure investments might not be the best way to build a country or a portfolio. Speaking of which, Growth At a Reasonable Price remains to this day a robust investment strategy. It seldom wins short races, but it helps finish most if not all long ones.

  18. paulski0 says:

    I haven’t come across this line of discussion before so I’m a bit confused about what’s meant by a “requirement” to meet net-zero here. Is this literally as dumb as people arguing that if we’re not heading for RCP8.5 we don’t need no stinkin’ climate policy?

  19. paul,
    I was trying to avoid linking to silly articles, but I can’t even now seem to find the one that initially motivated this. It was essentially as silly as you suggest, and if I can find it, I’ll put a link in a comment.

  20. Chubbs says:

    Willard, Thanks, I must admit I threw in the “iron law” without much thought and without looking up the definition. As you say there isn’t a dichotomy between economics and climate today as fossil fuels lose competitive advantage. You might say that the iron law, like rcp85, is a victim of clean-energy technologies.

  21. Everett F Sargent says:

    I’m still going with RCP 8.5 as being much more likely than Net Zero by 2100. I’m doubly on board with whatever SBM says! Oh and being dismissive of both Net Zero and RCP 8.5 coming to pass in 2100, is that like double or nothing?

  22. Ken Fabian says:

    Seems to me the low range scenarios are all predicated on low emissions – no matter the doubt, deny, delay crowd seeking to interpret those as somehow indicative of potential for low climate sensitivity, ie that minimal warming is what we should expect WITHOUT emissions reductions. Given there’s been more than 1C of global average warming from past, slower rates of emissions and current emissions, whilst growing less due to the efforts that are being made, are still running at record highs, we can expect the rate of warming to remain at or above current levels until actual emissions rates decline.

    8.5 still seems very possible to me – that there are influential, well connected interests that see such emissions as a natural right, whilst rejecting and creatively evading all responsibility for the consequences of them. We can still get there, just a bit slower.

  23. Susan Anderson says:

    Lyrics are magnificent: “Liar liar world on fire” [etc.]

  24. Susan Anderson says:

    Dolly Parton, Jane Fonda – https://firedrillfridays.org/

    9 to 5: now where’s Lilly Tomlin. We need real power, not just words.

  25. I read a piece in the Guardian that suggests that some of the carbon offsets being claimed by industry may not perform at 100%. I wonder if this kind of thing is part of the calculation for our plan to hit net zero?

    “A new investigation into Chevron’s climate pledge has found the fossil-fuel company relies on “junk” carbon offsets and “unviable” technologies, which do little to offset its vast greenhouse gas emissions and in some cases may actually be causing communities harm.” https://www.theguardian.com/environment/2023/may/24/chevron-carbon-offset-climate-crisis?utm_term=646dfc48639b44df9c916c1f18909c89&utm_campaign=GuardianTodayUS&utm_source=esp&utm_medium=Email&CMP=GTUS_email

    My guess is that some corporate carbon offsets being claimed will perform above expectations and will serve to make up whatever slight problems may appear and be reported this way.

    I love net zero because I think it can allow us to extrapolate some offsets and technologies that may not be fully tested and proven to perform as advertised. The freedoms offered to industry in this way can allow us to calculate our net zero plans even as we continue to protect shareholder financial interests.

    I am convinced that we can develop a great plan to achieve net zero. It pencils out for me.

    I think once we agree that we have solved the CO2 issue through our net zero efforts, we can swing our steely gaze on to the matter of slamming the door on methane emissions. I have some ideas about reaching net zero on methane that I think will scale out nicely and can be monetized.

    Nothing to this net zero thing.

    Here is a cheery article about reasons for optimism regarding climate change. https://theconversation.com/climate-damage-is-worsening-faster-than-expected-but-theres-still-reason-for-optimism-4-essential-reads-on-the-ipcc-report-202116

    Great weather in the PNW this week! Watering the strawberries and watching the grape crop start to develop.


  26. Susan Anderson says:

    SmallBlueMike: agreed, except that big corporate (especially big fossil, big ag, big plastic, and big marketing) is better equipped to game the carbon offsets and zero carbon situation than people who actually want to, you know, make a future for us all. And that’s after their lobbyists have managed to claim that things like natgas are “green”.

    Shiver me timbers!

  27. Everett F Sargent says:

    I guess 😀 one of the nice things about net zero is that it will always be out of reach. The carrot, if you will, to humanity’s stick. No matter how hard you try, the proverbial hill only becomes steeper. But alas, don’t give up, never ever give up, humanity is not an abject failure, as long as there are unobtainable goals before you to achieve someday, always someday.

    What comes after net zero? Dying! No wait. Mind you, as the next Western societal meme to hand wave over anthropogenic climaate change? Hopefully it ain’t geo___________ that these non-doers, meaning you all, come up with. It will probably have to be adaptation as is the only pragmatic and real choice here.

  28. I have truly and completely absorbed the message that it is not helpful to doomscroll through the news and science and get alarmed because once a person is alarmed, they will start making alarmist statements and that is counterproductive. The folks at this website have really been critical to my understanding of this alarmist process and its deleterious impacts.

    I used to laugh at the notion of netzero because I thought the target would be gamed by powerful parties who would manufacture the illusion of real carbon emission reductions and probably monetize and profit from their parts of a netzero charade. But I now take netzero very seriously and feel elated every time I hear the term and I think this has greatly improved my ability to read through the news.

    As Rust Never Sleeps notes above, it seems possible that we can hit 75% of net zero rather handily and that accomplishment comes with a great slashing of CO2 emissions. I read in the Guardian that the Russia/Ukraine conflict had greatly increased investment in green energy technology. You can read that here: https://www.theguardian.com/environment/2023/may/25/invasion-of-ukraine-has-fuelled-funding-boom-for-clean-energy See that? Even a military scrap like the Russia Ukraine conflict turns out to be a cloud with a silver lining. My guess is that when the war smoke subsides we will be looking at a new Ukraine where the ability to manufacture large amounts of CO2 has been greatly reduced through a return to an agrarian life style for much of the land that has been cleared through the military actions. The loss of life is distressing. But I don’t dwell on that.

    So much good news! I notice that the Guardian had this piece about increased investment in green tech under a heading of climate crisis and I think it makes more sense to discuss this as a climate opportunity.

    I think if we accentuate the positive and relentlessly reframe the “crisis” as an opportunity, then everyone stays happy and just keeps on reducing emissions as we have been doing over the past few decades.

    If you look at the data from the past few decades, it is clear to see how much we have already reduced our emissions and the rate of emission reduction is alarming. At some point we may need to consider the possibility of overshooting our emissions and crashing down through the 350 ppm mark or even down through 280 ppm. It is important that we stay cheerful and optimistic.

    Don’t get alarmed and going all doomy and alarmist. Look at how we are doing on CO2! It’s crazy! We are well under 430 ppm already. Our emission reduction plans are killing it. Yeah, Baby! Net Zero. Makes me smile.

    Daily CO2
    May. 24, 2023 = 423.70 ppm
    May. 24, 2022 = 421.27 ppm

    co2.earth, of course

    have to cruise to the lab for a little blood work. Going to be a beautiful day in the neighborhood here in the PNW.

    Please don’t be alarmed or alarmist.


  29. Willard says:

    Zeke needs no sardonicism to convey his point:

    At the same time, a world of 2.6C by 2100 is still a giant mess to leave to the future, including today’s young people, who will live through that, and warming continues after 2100 in these current policy scenarios. Climate system uncertainties mean that we could still end up with close to 4C warming if we get unlucky with climate sensitivity and carbon cycle feedbacks.

    Its also important to emphasize that current policy scenarios represent neither a ceiling nor a floor on future emissions. While we’ve seen a ratcheting up of policy in the past, we can’t preclude a world that backslides on both current commitments and policies, increases subsidies for fossil fuels, or otherwise leads to higher future emissions than we expect.

    Ultimately, the progress we have made should encourage us that progress is possible, but the large and growing gap between where we are headed today and what is needed to limit warming to well-below 2C means that we need to double down and light a (carbon-free) fire under policymakers to ratchet up emissions reductions over the next decade. Flattening the curve of global emissions is only the first step in a long road to get it all the way down to zero.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.