Worst case scenarios, or not?

I’ve been thinking a bit more about the debate around high emission scenarios, which I found rather frustrating. I think it’s an important issue, but the manner in which some people choose to frame this does make it difficult to have a serious discussion about it.

However, it does seem as though we no longer live in no climate policy world and, hence, it’s now very unlikely that we will follow an emission pathway that could lead to an RCP8.5 concentration pathway. This is – in my view – a very good thing and does mean that we may already have done enough to avoid some of the more extreme outcomes. On the other hand, I do think one should be careful of how to interpret this.

Credit : IPCC AR5 WGI SPM.10

The figure on the right shows the relationship between cumulative (total) emissions and warming. If we’ve largely now ruled out an RCP8.5 concentration pathway, then we may well have ruled out more extreme levels of warming (> 4oC, for example). However, it seems that we may still not have ruled out something close to an RCP6-like concentration pathway. Given the range of warming associated with this pathway, this could still lead to something close to 4oC of warming, which some regard as potentially having extremely serious consequences.

The other issue, which (somewhat ironically) those who criticise the use of RCP8.5 also point out, is that achieving some of our stated targets is going to be incredibly difficult. The figure on the left shows mitigation pathways that would give us a 2/3 chance of limiting warming to 2oC. If we’d started reducing emissions in the mid-1990s, we could have done so relatively gradually. Today, we’d need to halve emissions in about 15 years and get to almost zero emissions by around 2060; an extremely challenging prospect. Plus, there would still be a roughly 1/3 chance that we could do this and still end up with warming exceeding 2oC.

So, although it seems great that we may already have done enough to avoid some of the more severe outcomes, we still aren’t doing enough to achieve our stated targets and are still heading for a level of warming that could lead to very serious consequences. Furthermore, there are still factors that are uncertain, such as climate sensitivity itself, and how the carbon sinks are likely to respond as we continue to emit CO2 and, hence, continue to warm.

So, as much as I’m pleased that it appears that we’ve already implemented enough climate policy to avoid what might be regarded as a worst case scenario, it still appears that we’re heading in a direction that could still lead to pretty severe impacts. Just because the outcome is unlikely to be as catastrophic as it could have been does not mean that there’s nothing left to do.

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47 Responses to Worst case scenarios, or not?

  1. Steven Mosher says:

    glad we can agree that we dont live in a “no climate policy” world and probably never will again.

    as you note that still leaves many open and uncertain parameters. exploring those are what models are for.

  2. Steven,
    You highlight something that I think often gets missed in these discussions. As far as I can see, energy/policy people seem to link the RCPs with socio-economic pathways (SSPs) and, hence, judge them on the basis of how likely those SSPs actually are (even if there aren’t really any probabilities associated with them). On the other hand, climate modellers – as far as I can see – simply regard the RCPs as bracketing the range of possible concentration pathways (from one that is now probably too low to be realistic, to one that is a worst case scenario). Hence, they’re perceiving them somewhat differently and also using them for slightly different purposes. Might be good if these differences were at least acknowledged and that people would try to understand the reasons why they might have different motivations for using these RCPs.

  3. Chubbs says:

    Guessing phsycology plays a role. Easier to criticize a distant and uncertain RCP8, than focus on the certain near-term path to 2C.

  4. Joshua says:

    Anders –

    What was your problem with the Pielke article. It seemed fairly reasonable to me, outside of that makes unsupported claims about the results of “misuse” of 8.5 (it handwaves some claims about some damage form that “misuse” but doesn’t really describe what they are in any meaningful detail, and completely fails to support the putative cause and effect).

    One question I have about the article is that it sites the nytimes and financial times articles as claiming 8.5-associated outcomes as those that are most likely or exclusively those that would result from BAU, but doesn’t quoute the IPCC to prove that those outcomes are only associated with 8.5 in the IPCC report. Perhaps sloppy but not inaccurate on RPJr’a part?

  5. Joshua,
    I just think calling other people’s research “climate porn” is sub-optimal. Each to their own, of course. [Edit: okay, the title is “to generate climate porn”, but I still think this framing is sub-optimal]

  6. Joshua says:

    Anders –

    W/r/t my comment above…

    > . Might be good if these differences were at least acknowledged and that people would try to understand the reasons why they might have different motivations for using these RCPs.

    I think RPJr. actually did that in the article, (somewhat to my surprise, which perhaps was due to my own prejudices).

  7. Joshua says:

    Yeah – the “climate porn” framing is sensationalistic (and pathetic). That’s the kind of shit that completely runs counter to RPJr.’s front-facing facade of plausible denuability.

  8. Steven Mosher says:

    “Hence, they’re perceiving them somewhat differently and also using them for slightly different purposes. Might be good if these differences were at least acknowledged and that people would try to understand the reasons why they might have different motivations for using these RCPs.”

    I would actually think of two separate sets of scenarios.

    ‘pure’ analytical types of scenarios ( rcp 1-8)

    policy centric scenarios grounded in real plans and goals.

    And a shift over time in how compute resources are allocated, or buy more compute

  9. Joshua,
    Yes, I don’t specifically disagree with some of the criticism of how RCP8.5 is used and reported. However, I do still think that it isn’t quite as unlikely as some suggest (given both uncertainties in our own socio-economic future and the response of the carbon sinks) and I think there are still valid reasons for using it in climate impact studies, even if the reporting on this is not always ideal.

  10. Steven,
    Yes, I agree that it night be worthwhile to distinguish between concentration/forcing pathways used as inputs to climate models that are then used to assess the range of possible impacts, and pathways that come out of studies that try to understand something about what sort of socio-economic pathways we may actually follow.

  11. Joshua says:

    Funny thing about the “climate porn” syntax. I read that headline and then looked at the byline and saw no “Jr.” And so I thought to myself that dad must have adopted his son’s unfortunate rhetoric – and was a bit surprised. Then I got to the end and saw that it was Jr. after all.

    And order was restored to the universe once again.

  12. paulski0 says:

    Joshua,

    What was your problem with the Pielke article.

    Actually, there were some things I didn’t expect which seemed positive in the article. He actually acknowledged that RCP8.5 is a business as usual scenario within a range of business as usual, something he was very dismissive about when I said this to him a while back.

    There was one important thing which doesn’t seem right, though it appears to come from a reasonable interpretation of a confusing statement by Detlef van Vuuren. It claims that RCP6 is (if any) the most likely to be a business as usual pathway. However, this was accompanied by van Vuuren also suggesting most likely was about 6-7W/m2 (presumably by 2100), whereas the RCP6 pathway only has a 2100 forcing of about 5W/m2 (because the 6 refers to forcing reached at stabilisation in the 22nd Century, not at 2100). If you look at all the SSP range and AR5 scenario range graphs comparing with RCP pathways RCP6 is actually equally extreme at the low end as RCP8.5 at the high end.

  13. As the emissions scenarios take a sensitivity figure of 3C as one of their assumptions, all of the RCPs are vulnerable to changes in the outcome of that debate. RCP 8.5 has been obsolete for almost a decade, as I (among others) were quick (and perhaps too quick) to point out.

    It would not have been rocket science to provide estimates of temperature increase (or other relevant metrics) for each RCP using more than one sensitivity estimate. It is still the central question in the climate debate and it is still not resolved.

    It is often difficult to recall during the climate conversation that the RCPs were commissioned to provide inputs to models, not as the result of any calculations. The socio-economic rationalizations of ‘how the RCPs got there’ were admittedly speculative in nature and the warning labels on the tin were there from the beginning. Pielke is right that those warning labels were ignored by activists, lobbyists and a handful of scientists.

    If sensitivity is 3C or higher than an RCP of 4, 6 or 8.5 will be damaging to our wealth and health. If it is 2C much less so. The metric of interest is the proportion of our fuel portfolio is provided by coal. And we’ve taken our eye off the ball on that one and have failed to provide the developing world with an alternative they could actually use.

    We have collectively been mumbling in a corner about arcane trivia instead of helping underdeveloped countries jump a rung on the energy ladder. That is something that future generations may find it hard to accept.

  14. Tom,

    As the emissions scenarios take a sensitivity figure of 3C as one of their assumptions, all of the RCPs are vulnerable to changes in the outcome of that debate.

    What do you mean by this? When an RCP is used as input to a climate model, there is no initial assumption about climate sensitivity.

    It would not have been rocket science to provide estimates of temperature increase (or other relevant metrics) for each RCP using more than one sensitivity estimate.

    That’s what the broad band in the figure represents. In a sense, that’s one of my points. Even if we have avoided following an RCP8.5 concentration pathway (and I’m not as convinced of this as some seem to be) the range of warming associated with the lower RCPs does not rule out that we could still undergo substantial warming (and the associated impacts).

    If sensitivity is 3C or higher than an RCP of 4, 6 or 8.5 will be damaging to our wealth and health. If it is 2C much less so.

    I’m not entirely sure what you mean here, but if climate sensitivity is low, then the impacts will almost certainly be less severe than if it is high. However, we can’t yet definitively rule out that it won’t be high, so even if we have avoided an RCP8.5 concentration pathway, we have still not definitively avoided a level of warming that could have a substantially negative impact.

  15. Yes, ATTP, I should have been clearer–the socio-economic speculations and the scare stories that followed should have employed differing sensitivity estimates.

    But imagine you’re Modi in India trying to plan for your country’s ongoing development. You have mountains of coal under your feet, even if you’re currently importing more than you’re digging up. Your energy trajectory will almost certainly have a more dramatic slope than China’s has over the past 3 decades. Your job and that success of your party depend on continued economic growth.

    Who has come to you with a plan that includes an alternative to coal? Who has offered a Lend-Lease program for nuclear, hydro, wind or solar? No-one. You don’t have the financing to do it on your own and you have other extremely pressing needs that you must address to keep your job.

    Who among you (us) has come up with a plan that would help meet India’s needs?

    Because CO2 is a well-mixed component of the atmosphere, we forget that human emissions are not truly a global phenomenon. The top five emitters account for a very high proportion of all emissions–the second five are responsible for only 11% and it drops drastically after that. And that skew will get more dramatic during this century, even if the names of some in the top two tiers will change.

    Where is the specific and targeted plan for India for this generation and for Indonesia and Nigeria for the next?

    We are straining at gnats and walking in camel dung.

  16. Sure, we should be fine. We have done so much already that it’s easy to see the health of the oceans rebounding right before our eyes. The sixth extinction has stopped in its tracks. Discussion of RCP8.5 can and should go away so we can have a less emotionally charged discussion about climate change. Or maybe just dump that discussion altogether and just talk about cap and trade or BECCS or breeder reactors? Keep it positive, stop scaring people.

    Rags like the Atlantic should stop publishing drivel like this:

    “Are we currently on the worst-case scenario for climate change?
    “We’re actually a lot closer than we should be; I can say that with confidence,” says Rob Jackson, an Earth scientist at Stanford and the chair of the Global Carbon Project, which leads the research tracking worldwide emissions levels.”

    https://www.theatlantic.com/science/archive/2019/01/rcp-85-the-climate-change-disaster-scenario/579700/

    Who is this Rob Jackson? What a crackpot he must be.

    Thanks for raising your voice of reason on behalf of throwing out RCP8.5

    Mike

  17. It’s well known that editors choose the titles of news and opinion articles and not the writers. If I were the editor I would have chosen the documentary category. The pathway to RCP8.5 is set when the low grade and low EROEI fossil fuels start to get extracted to make up for the exhaustion of high-grade crude oil supplies — guaranteed twice as much emissions for the same usable energy.

  18. Tom,

    Where is the specific and targeted plan for India for this generation and for Indonesia and Nigeria for the next?

    Yes, I agree that this is an issue. But that’s part of what I’m getting at. Serious people are claiming that an RCP8.5 concentration pathway is essentially impossible and yet, at the same time, pointing out how difficult it is going to be to decarbonise while the developing world also continues to grow and develop. Having said that, I do think we probably won’t end up on an emission pathway that could lead to an RCP8.5-like concentration pathway, but I’m not as convinced that this is quite as impossible as some seem to suggest.

  19. Can you name three of the most serious people who claim that an RCP8.5 concentration is essentially impossible, please>

  20. Mike,
    I actually thought that the Atlantic article was pretty reasonable. Three serious people who suggest that it’s impossible? Well, there’s Glen Peters, Justin Ritchie, and (I guess) Roger Pielke Jr. I’m not sure they’re quite saying “impossible”, but they seem to be suggesting that it’s become very unlikely, or even virtually impossible.

  21. “This scenario could still be in the planet’s future, according to Zeke Hausfather, an analyst and climate scientist at Berkeley Earth. Since 2005, total global greenhouse-gas emissions have most closely tracked the RCP 8.5 scenario, he says. “There may be good reasons to be skeptical of RCP 8.5’s late-century values, but observations to-date don’t really give us grounds to exclude it,” he recently wrote. …Yet not all data suggest that we’re doomed to RCP 8.5 or equivalent amounts of warming, Hausfather cautions. If you look only at pollution from fossil-fuel burning—and not from land-use events like deforestation—then humanity’s recent record trends closer to RCP 4.5.”

  22. Tom,
    Yes, Zeke’s comments on this seem perfectly sensible to me.

  23. Yes, I also find the Atlantic article to be pretty reasonable. I do not find arguments from Glen Peters, Justin Richie, and maybe Pielke Jr. persuasive enough to agree that RCP8.5 should be taken out of picture. I think the known and unknown unknowns are potentially too significant to agree that RCP8.5 can be discarded. But hey, that’s just me. I also carry fire insurance on my home and occasionally consider the very unlikely scenario that my old stucco/lath and plaster home could catch on fire. I guess if I really absorbed the unlikely, virtually impossible scenario of a house fire in this largely cement wrapped structure, I could just let all that go. My insurance agent tells me it is silly to worry about climate change, but he thinks it’s important that I keep up the fire insurance. It’s all very strange, is it not?

    You don’t want to get me started on all the tsunami signage at the coast. Isn’t that a complete waste of money when generations of humans are born and die without ever having to evacuate from the very unlikely occurrence of a tsunami? Tsunami porn, I guess.

    Cheers

    Mike

  24. I guess this is politics and not science, so let me repeat myself: This is the scenario Trump, WUWT & Co. and the far right parties of continental Europe are fighting for. If you look back a century these kinds of people have brought enormous suffering to humanity and I see no reason to be confident that humanity has learned enough from history that we can be confident this does not happen again.

    Feel free to give it another name. One should not call it unrealistic without calling the best case scenario unrealistic.

  25. paulski0 says:

    then humanity’s recent record trends closer to RCP 4.5

    Yes, though it should be pointed out that the RCP4.5 he’s talking about is a fairly strong mitigation scenario in which mitigation doesn’t properly start to kick in until a decade or so from now. That is, if we say we’re following close to RCP4.5 now we really mean we’re currently following close to a baseline scenario which then later branched to result in a 4.5W/m2 forcing due to climate policy introduced in the very near future. So being relatively close to RCP4.5 now doesn’t mean anything at all about forcing at 2100. At most it means we’re heading for something like whatever forcing the prior baseline scenario would have produced. We’d only continue to follow RCP4.5 if we implemented similar strong climate policy.

    As another example, the SSP-4.5 scenario actually tracks almost exactly with SSP5-8.5 until 2040 before a rapid mitigation program kicks in.

    Though even among baseline scenarios SSP5 (the highest at 2100) is at the median of SSPs at 2020 so it’s not clear that we get much information about the future from emissions to date.

  26. Paul,
    I think RCP6 is also regarded as a rather odd emission pathway because the emissions till about 2030 are below all the other pathways. It’s one reason (I think) why it’s rarely used and, hence, why most models are run with either RCP4.5 or RCP8.5.

  27. Willard says:

  28. Willard, yes, that was one of the reasons I’d been thinking about this. There do seem to be many factors that could influence future emissions pathways.

  29. paulski0 says:

    Well, I’ve had a look at the RCP4.5 paper and it does detail the baseline/reference scenario used. Turns out there is a small mitigation influence up to now, though 2018 fossil fuel emissions are pretty much exactly on the reference rather than mitigation curve according to the Global Carbon Project estimate. The reference scenario results in 2100 CO2 of 792ppm and total forcing about 7W/m2.

    Aside from that even there does seem to be a reasonable consilience of evidence towards a likely no (or minimal) policy outcome of close to 7W/m2 by 2100. Though, as I’ve said before, a very important point which is often skipped over here, is that the majority of baseline 7W/m2 2100 scenarios would very clearly hit 8.5W/m2, based on their trajectories, within a few decades of the 22nd Century.

  30. paulski0 says:

    I’ll put that another way. The main reason presented in Pielke’s article for suggesting consideration 8.5W/m2 impacts should be eradicated/substantially downplayed is that that level of forcing is in the tail of the baseline scenario distribution. However, if you look at the trajectories of the five baseline SSPs at the end of the 21st Century and extrapolate, three of the five reach 8.5W/m2 by about 2130. So if we arbitrarily picked 2130 as the end date rather than arbitrarily picking 2100 then 8.5W/m2 would go from a fringe possibility to perhaps the most likely baseline outcome. Though of course, RCP8.5 by 2130 is up to about 10W/m2.

  31. David B. Benson says:

    I’m with Willard. Here is some inkling of just how bad things will become in South Asia, the most populous part of the world.:
    http://bravenewclimate.proboards.com/thread/697/power-world?page=3#post-5971

    We won’t overcome without India, although that is not sufficient, merely necessary.

  32. ATTP:
    “I just think calling other people’s research “climate porn” is sub-optimal. “
    Quite so– the term should be reserved for performance art:

    https://vvattsupwiththat.blogspot.com/2019/10/gretas-mom-tweets-thanks-for-nobel.html

  33. Steven Mosher says:

    Zeke is always sensible. You have no idea how annoying it is.

  34. Steven Mosher says:

    Tom

    “We have collectively been mumbling in a corner about arcane trivia instead of helping underdeveloped countries jump a rung on the energy ladder”

    One approach is to issue/support Green Bonds. we could even put them on a blockchain.. haha.

    I think some canadian provinces have experimented with this. I dont know why it isnt a
    larger push on the activist side.

    You want green power, Invest in green bonds. Say a Bond that only funds solar in India, etc etc.

    It really is confusing to see that these options for funding green power are there but there is no marching in the streets for it.

    Instead we have the chinese road & belt. expanding use of fossil fuels in the developing world.

    Its weird. Imagine a world where someone like Greta would Push to take action and buy green bonds. Never happen. its much easier to say dont fly, dont eat meat, dont use plastic, dont dont
    dont dont. Much harder to say do put your money into a green bond. weird.

  35. Chubbs says:

    If we were willing to address climate change honestly, by recognizing the problem and taking cost-effective measures, then RCP85 would be a ridiculous scenario. However, I don’t see enough evidence yet that this is the case. In another recent Forbes column Pielke argues for a $1 per ton CO2 tax which would increase the price of gasoline by less than 1 cent per gallon. Hard to take him seriously in a scenario discussion until he comes up with something better than that.

  36. Clive Best says:

    The long term goal is to stabilise CO2 levels in the atmosphere at some reasonable level. Does that mean that we must reduce net CO2 emissions to zero? This is what models of the carbon cycle imply, but I doubt whether this can be true. In the past volcanic activity was much higher and yet CO2 levels stabilised albeit at higher atmospheric concentrations. If we can just stabilise emissions at a lower level CO2 levels may simply taper off as the sinks slowly adjust.

    This paper is interesting Scientists quantify global volcanic CO2 venting; estimate total carbon on Earth

    If you calculate the fraction of carbon on earth you get 330ppm !

    Total carbon on earth = 2*10^21 kg
    Mass of earth = 6*10^24 kg
    So Carbon is 330 ppm of earth’s total mass

    What a coincidence !

  37. paulski0 says:

    Clive,

    Does that mean that we must reduce net CO2 emissions to zero? This is what models of the carbon cycle imply

    Depends on what you define as a reasonable level but carbon cycles models say we can quickly stabilise at current CO2 concentration with about an 80% emissions cut. To stabilise at a lower level would require something closer to zero for a while.

    If we can just stabilise emissions at a lower level CO2 levels may simply taper off as the sinks slowly adjust.

    Probably, yes, though it’s theoretically plausible we might pass some threshold which sees us transition to a hothouse-type carbon cycle configuration and CO2 levels tending towards higher levels rather than lower. But even assuming we do taper long-term you’re talking about timescales of thousands of years, which aren’t very relevant given that we rarely seem to acknowledge that the world will still exist just 30 years after 2100.

  38. verytallguy says:

    paulski nails the end of century issue.

    regarding 2100 as the end of the world by IPCC and others means the implications of the trajectory of emissions at that point *and* the fact that the most severe impacts are beyond 2100 are ignored.

  39. Clive,

    The long term goal is to stabilise CO2 levels in the atmosphere at some reasonable level.

    Depends. The long term goal of many is to stabilise global warming (i.e., temperatures). This would require getting net emissions to zero. Stabilising concentrations would mean continued warming. Also, if we don’t eventually get emissions to zero, concentrations will ultimately continue rising.

    This is what models of the carbon cycle imply, but I doubt whether this can be true. In the past volcanic activity was much higher and yet CO2 levels stabilised albeit at higher atmospheric concentrations.

    Yes, but if the concentrations are higher, then the slow carbon cycle is faster and the system could still be in balance (volcanic emissions balanced by uptake through the slow carbon cycle). Given we still have volcanic emissions, the level of emissions that would allow us to maintain a roughly constant atmospheric CO2 concentration is low, and would have to continually decrease (because we’re continually adding new CO2 to the system, rather than recycling CO2 through the system).

    What a coincidence !

    Yes, I’m pretty sure it is.

  40. Just to follow up on this

    If we can just stabilise emissions at a lower level CO2 levels may simply taper off as the sinks slowly adjust.

    Yes, this will happen, but the timescale is long (thousands of years).

  41. Using Clive’s argument, the amount of iron by mass in the atmosphere should be 350000 PPM. Clive, you’re off your game, way too smart for this 😜

  42. Clive Best says:

    Iron is too heavy ! Just like hydrogen is too light. 😉

  43. Coincidence is too convenient !

  44. anoilman says:

    In a post fact world, Correlation = Causation.
    https://www.tylervigen.com/spurious-correlations

  45. Willard says:

    Zeke did another thread:

  46. Clive is always an inspiration –

    Cue proposals to cap future CO2 levels by limiting trade in hydrocarbons to those based on capture of carbon-14 from the atmosphere.

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