After the whole RCP8.5 fiasco, that some may remember, I got interested in thinking more formally about modelling scenarios. I even contacted a philosophy colleague to discuss the possibility of working together on philosophy of science aspects of this issue. A lack of direct relevant expertise, and a lack of time, meant I didn’t really take this any further. However, it is still a topic that I find interesting.
Any modelling will require some assumptions about the system being studied. If you want to understand how our climate might change, you need to consider possible future emission pathways. If you want to understand how a virus might spread, you need to consider what we might, or might not, do in response. This is essentially what we mean by scenarios in this context.
The choice of scenario will depend on the motivation behind the work. It might be a purely scientific question: how will the system evolve under these conditions? It could be purely modelling: how does a new model compare to an older model when using the same scenario? It could be to inform policymakers: what should we do to avoid this outcome, or what will probably happen if we follow this pathway?
One of the criticisms of RCP8.5 in climate modelling is that this pathway is implausible, but has been presented as a business-as-usual pathway. Although a reasonable criticism, much of the rhetoric around this was, in my opinion, too extreme and ignored the many valid reasons for considering this kind of scenario. I don’t want to rehash my arguments again, but I did write a number of posts that you can probably find if you’re interested.
The climate science community is now in the process of developing the scenarios for the next IPCC Assesement cycle and, unsurprisingly, the usual suspects are claiming that climate science is about to make a huge mistake because, despite advice to the contrary, they’ve chosen – again – to assign the most extreme scenario its highest priority.
Given the seriousness of this issue, and that the criticism seems to be getting quite a lot of traction, I thought it important to read the original paper that presents a perspective on the next generation of Earth system model scenarios. As far as I can see, it is not assigning the highest priority to the most extreme scenarios. It also seems to have considered most of the criticisms of scenarios, discusses the different uses for scenarios, including high-end pathways, and highlights that it would be beneficial to separate high forcing pathways for scientific purposes from the more policy-oriented framing pathway categories.
So, once again, it seems that the criticism is – at best – wildly exaggerated, or – at worst – completely misrepresents what’s being done. Of course, the latter would probably not surprise some people. It’s always been pretty clear that much of the criticism of RCP8.5 was motivated more by a desire to find something to criticise, than by any desire to be constructive. The same seems to be the case here. To be fair, if you’re a bad faith actor motivated by a desire to simply find something to criticise, it must be tricky to know how to respond if those you’re criticising actually take your initial criticisms seriously.
...and Then There's Physics 
I reposted the closing paragraphs on The Climate Wars
Whilst the timeline may be longer the notion that using ever more fossil fuels without restriction ie getting to 8.5 and beyond, just slower, remains a desired outcome of a still popular and influential mainstream movement still fiercely opposing and obstructing decarbonisation – certainly it a still popular political donor desired position. These interests achieving their objectives should not be considered entirely impossible even now; the depth of their commitment to saving fossil fuels from global warming (and renewable energy) should not be underestimated. Truth is the least of the collateral damage they are willing to tolerate.
Admittedly it looks much more difficult for that kind of fossil fueled future with solar PV costs looking ever more like Zeno’s race as it approaches but cannot ever reach zero and batteries having similar cost and growth curves. And it is turning into an Aesop’s race for ICE vehicle manufacturers who got what they wanted – don’t want to, don’t have to – and their big fear now is that China will mass manufacture EV’s too cheap and will flood the world with them. Can’t make this stuff up. Even a decade ago a “problem” like that that really did look impossibly optimistic but… only for lack of trying.
(attempting a comment with a new email address – wordpress will not unlink the old one and my secondary one didn’t like the email comment option.)
“Admittedly it looks much more difficult for that kind of fossil fueled future with solar PV costs looking ever more like Zeno’s race as it approaches but cannot ever reach zero and batteries having similar cost and growth curves. And it is turning into an Aesop’s race for ICE vehicle manufacturers who got what they wanted – don’t want to, don’t have to – and their big fear now is that China will mass manufacture EV’s too cheap and will flood the world with them. Can’t make this stuff up. Even a decade ago a “problem” like that that really did look impossibly optimistic but… only for lack of trying.”
Except some of us predicted exactly that. And got called bad faith actors as a result.
Tom,
Really, is that what you were saying, or is it what you want people to now think it was what you were saying?
Interesting recent development in scenario land is the publication of new underlying socio-economic projections for SSP1-5 that will be used in updated SSP scenarios. Biggest surprise is probably in population, with big upward revisions compared to those made a decade ago. Median (SSP2) 2100 population is up from 9 billion to 9.9 billion, extreme low growth (SSP1) up from 6.9 billion to 8 billion and extreme high growth (SSP3) up from 12.6 billion to 13.1 billion.
Worth noting that IIASA, the group producing these projections, had a median expectation of 8.4 billion just 15 years ago. When considering the confidence we should place in predictions about “most plausible” scenarios over the next 80 years we should keep in mind this case where the median expectation 15 years ago is now considered to be in the region of very unlikely.
Despite higher population growth in all SSPs, they also all have significantly lower GDP growth from 2010-2100 than the previous edition. Though this is mostly about the much lower than expected growth over the past 10-15 years rather than future growth.
This would probably indicate a hypothetical median no policy baseline of a little over 3.5C compared to about 4C in the previous version.
Paul,
Indeed. Trying to make predictions about the future is inherently difficult, especially for multi-decade timescales. I think it’s fine to have some confidence that we can, for example, implement alternative energy sources that ultimately replace all fossil fuel sources. However, to completely dismiss that we might not, or that things might happen to disrupt that process seems wildly over confident.
I do have some sympathy with those who complain that there’s been too much focus on worst-case scenarios, but that doesn’t mean that we shouldn’t consider them.
This question of scenarios is never going to go away – too lucrative for the “bad faith actor motivated by a desire to simply find something to criticise.”
Models have inputs, and create outputs. A standard part of model development and use is the “sensitivity analysis”. This is a process where inputs are changed over a reasonable range, and changes in output are tracked. This way, you can determine what factors affect model outputs, and whether those outputs change enough to be considered important.
Take the model Y = mX + B. We can actually use Calculus in the case, differentiate with respect to X, and determine that the sensitivity of Y to changes in X is determined by the parameter m. Never learned Calculus? Try several values of X, calculate Y, and (hopefully) notice that the change in Y is a constant multiple (m) of the change in X. We’ve just done a sensitivity analysis of the model Y = mX + B.
Calculus won’t work on a complex model, but a sensitivity analysis will. It’s basically numerical differentiation.
If large changes in an input have little effect on the output of interest, then you can accept large uncertainties in that input variable and still be confident in the output value. If small changes in input values have large effects on outputs, then that tells you that you really need to nail down the correct values for those inputs to make accurate predictions.
This exercise is useful whether you are simply trying to understand the system, or trying to develop policy. And it is a good idea to look at the extremes of input ranges – not just the centre zone. If your model starts doing strange things at the extremes, it can serve as a warning sign that something might be wrong in the model.
Next stage is “how do we compare two or more models?”. In such cases, you absolutely need to make sure you have consistent inputs for all models. When model output differs, you won’t get answers to why if you had different inputs. After all, a single model will have different outputs with different inputs – so why would you not expect two different models to have different outputs for different inputs, even if both models are an excellent representation of reality?
Enter the “scenario” – nothing more than a commonly accepted grouping of input values to start the models with. A way to ensure that the models have a common beginning point. Now, you can be sure that when output is different, it is due to model differences, not input differences. And choosing several scenarios is simply an agreement to try all the models with several different input combinations across a range of values.
And when you do another model comparison a few years later, when everyone has had a chance to improve (change) their models, you still want scenarios (inputs) that can be easily compared to the previous ones. Constantly changing the scenarios (inputs) gives you that “really hard to compare” situation again. Which is bad (unless you make your living simply finding something to criticise and beating the Uncertainty Drum).
It is a real shame that the Biden administration is jamming up import of chinese ev cars. It feels like there is an opportunity there to reduce global emissions slightly.
Mike,
Chinese cars are more relevant to Ned‘s drive-bys at Gavin’s than to this post. Go discuss this topic with him. You both seem to share an admiration with Lakoff’s work on framing.
as is often the case with your comments, I have no idea what you are talking about. https://www.bbc.com/news/business-69004520
Mike,
First, I’m telling you that you’re off topic. Second, I’m suggesting that if you’re to use sock puppets to channel different voices, you should at least be more subtle about it. Is it clearer this time?
You got one last comment on this thread. Use it well.
ATTP:
We should consider worst case scenarios , but must not forget the cautionary example of those that have run off the tracks on their own time lines, or turned into factoids.
As a matter of semiotic reality, popular culture often elides book & report titles with reality. Limits to Growth, The Population Bomb, and Six Degrees were all paradigmatic objects of discourse for a decade or more before being overtaken, like RCP 8.5, by critical inquiry and evolving data.
They, like semiotics itself, only lasted that long because it was unfashionable to question them-
The models, and in spite of efforts to the contrary, are simply mental imaginings hammered out in the minds of humans. Physics is not, thereby, persuaded, rather, it is and simply remains the “There” that it is. This “There” remains an inconvenient truth, relative to academic hubris (if there is such a thing). &/or, consider this comment’s content that’s often been afforded the privilege of a drive by here at this “There”:
The #InuitObservations of twice seasonal lifts in the Arctic tropopause and the resulting <1.4% additional solar insolance that is not in the models (but closes the gap between observations and models and Arctic sea ice loss), needs to be included in/added to this overview of the AMOC tipping thing. When it happens also shows up in the 2014 cessation of the AABW (Antarctic Bottom Water) recharging previously reported and discussed. Where and when stuff is stuff that is controversial, and thereby, for some, fun. What is not funny is that such is rather socially impertinent when the matter relates to thermalhaline circulation dynamics that are solar, not atmospheric CO2 concentrations related …& when one factors in that the IPCC Special Report on 1.5ºC, which asserted a stabilization in the climate forcing effect of CO2 a decade after atmospheric stabilization occurred was predicted on modeling that left the cryosphere out of its calculations. The cryosphere’s #FossilCold will be a factor in the physics of the ongoing collapse of the Holocene/rise of the Anthropocene …until its significance is statistically below another systemic tipping point in our loss of our cryosphere that is currently a willful blind spot in IPCC [involuntary] ‘groupthink’. <—#Orwellian?!?
If the link works, it is posted at Paul Beckwith’s YouTube channel here: https://www.youtube.com/watch?v=Qs2raUqUmsQ&lc=UgzTV7P4VWpaeixOsex4AaABAg.
Also what claims #AcademicPrivilege wishes to retain relative to rational reasoning needs to include – in its otherwise observational bias – is that with the hydrogen tax credits and securitization incorporated into the US’ 2022 IRA with that law and its tax credits, discredits the piety of that #AcademicPrivilege; reveals a meme of #MotivatedReasoning that hides, as it always does – at least once it is seen – in plain sight⁉️
🤷♂️ =)
>
This looks to me like it is rapidly getting to the inflection point where new energy supplies mostly come from clean sources, and emissions consequently start dropping (which hasn’t happened yet, 2023 was still a year of record emissions).
These scenarios will be seen in a different light once we start significantly diverging from ‘zero policy’ pathways in terms of emissions (I think in technology terms we already have), and the higher-end pathways become ‘avoided bad outcomes’.
Of course, at this point, we already have ‘missed good outcomes’, too.
There has been a huge amount of active human decision and will involved e.g. in the transition to EVs that looks like it will play out to an end-game quickly in places like China. I’m not certain it can be in any meaningful/useful sense be largely attributed to ‘policy’ and I think Koomey’s ideas about moving between local optima is also playing a big role.
Ben,
Yes, I agree. As far as I can tell, the paper that I reference in the post does indeed suggest the same, and they are describing the high-end pathways as being the “emission world avoided”, which are usefully scientifically and also to tell us what could have been. Of course, there will be some who will argue that they never, ever, ever, could have been, but that doesn’t mean that they’re right.
I’ll add, though, that there is an interesting issue about scenarios that I didn’t touch on in the post. There will be some scenarios that won’t emerge in reality because the impact of starting to follow such a pathway will preclude it from continuing. For example, the impact of an RCP8.5 pathway might be severe enough that we can’t actually follow one until 2100. Similarly, would society really “do nothing” when a pandemic is ongoing?
I think this is an interesting modelling question. Should we somehow include the impact of following a pathway on how that pathway evolves? Since this typically involve trying to model how societies will respond, my generally view is mostly “no”, it’s too complex. However, it is still worth considering this issue, in my opinion.
As well as being “too complex”, the main point of these models is to inform human choices, rather than predict them, which is only possible if you deliberately exclude some human choices from the modelling loop. i.e. to show what happens if we make certain choices.
This is partly a question of the role of scientists, which is traditionally to avoid making normative/value judgements, and just predict the outcomes of physical processes. i.e. act as a kind of broker for possible pathways, rather than an advocate.
I’m aware that the same people who complain about there being too wide a range of policy scenarios considered (only about one end of the range, obviously) also complain about scientists acting too much as avocates. However in the end, the aim is to get as good as possible an outcome for human society, and it doesn’t matter if contrarians go to their graves mouthing recriminations against scientists.
I have dozens of these, if not hundreds. How many do you want?
2/25/2013: “Those who have embraced the idea of a Grand Solution for climate change trivialize the contribution each human can make. This reduces the sense of accomplishment we can feel by conserving, changing fuels and participating at a community level. It also leaves the power and the glory to the Grand Solutionists. I somehow doubt that’s coincidental.
Fortunately, people have enough common sense to ignore them, and are busy installing solar panels on their roofs, solar water heaters throughout the world, buying more efficient cars and getting on with life in better insulated houses. At a minimum, they seem to understand something that the Grand Solutionists never will. Individual action may not change the climate–but it will change the politics, as those who answer to voters watch their individual actions and recognize they need to run in front of the parade so they can continue to pretend to lead it.”
2/22/2013
“In my recent series of posts prognosticating the trajectory of climate change during this century, I basically project that we are still in for a lot of warming due to huge increases in energy consumption, but that we will be ‘rescued’ by the growth of energy delivered by renewable sources, primarily solar.
I have nothing against wind, biofuels or hydropower. I’m sure they will grow and make valuable contributions.
But I can see what is happening in solar and I can connect it to the growth of past transformative technologies. I have faith in its growth.
Faith is kind of a dirty word when talking science and technology, but really–we all take actions based on trust or belief rather than checking every fact and item, else we would never board a commercial airline or eat a Big Mac.
Installations were 29 GW in 2012. In 2007 installations were 5 GW. In 2002 they were less than 1 GW. The global total is now over 100 GW in capacity.
That’s an asterisk in global production, amounting to less than 0.4% of electricity generated.
Solar power has been growing by 30% annually for the past two decades. If it continued to grow at that rate we would have 41,754 Terawatts in capacity.
I think we’d run out of sand first. At any rate it would be more electricity than we would actually need, even with growing population and higher living standards. About ten times as much, even accepting my outlandish projection of a need for 3,000 quads by 2075.”
Tom,
I suspect I wasn’t clear enough. I was suggesting that if you were indeed regarded by some as not engaging in good faith, it wasn’t simply because you were promoting a narrative suggesting that renewables would soon dominate over fossil fuel sources.
Anyway, I suspect it’s not worth anyone’s effort to try and litigate this issue. If you want to believe that you’re now being proven right and that your detractors were wrong, be my guest.
I’m happy to be your guest, ATTP and not just because of your hospitality. It is in fact because I do believe I’m being proven right and my detractors wrong.
It might be just for a season–but it’s a nice season.
Yes, I do get that. My suspicion is that the climate debate is going to evolve into a whole lot of people who think that they are being proven right, and their detractors wrong.
‘Twas ever thus, no?
If you mean it’s always been full of people who are convinced that they’re right, and never admit when they’re wrong, then yes, I guess it has.
Two scenarios:
https://www.youtube.com/watch?v=NGJu6kViRG8
Happy dads day!
@Ben – yes, the drivers of growth of RE have changed. Now it is primarily driven by… demand for electricity at least cost – crossing a tipping point that is more obvious in growth of investment in factories to make future RE/EV’s than in current stocks vs FF. Which I too am less inclined to attribute to significantly greater political policy ambition. More about taking near term advantage I think. Including, politically, of the declining effectiveness of alarmist economic fears of decarbonizing. The full effects of cost effectiveness have yet to play out.
But climate considerations aren’t absent, whether as commercial expectations in the face of emerging real world climate change harms, that emissions requirements and regulation will get tougher, insurance more expensive and even (very belatedly) willingness of courts to make accountability for climate harms more explicit, even potentially for findings of culpability, ie paying out damages.
Heh. Dr. Swain, whose profile calls him a “climate scientist-communicator”, goes on to say “It’s pathological at this point”. Now, that’s what I call climate-science communication!
Roger’s still right, of course….