In the last article – Opinions and Perspectives – 3 – How much CO2 will there be? And Activists in Disguise – one commenter suggested that RCP8.5 was actually “business as usual” and put forward some comments. So I’m posting this followup to identify some key points in that scenario, before going onto the next topic.
I’m trying to keep this series of articles brief and as non-technical as possible, but this one has to be a little more detailed.
It was excellent to find someone prepared to defend RCP8.5 as “business as usual”. We need more champions of this idea so it can be discussed. What key climate scientists should do is publish a paper “Why RCP8.5 is actually business as usual“. Or “How RCP8.5 has a serious likelihood of becoming reality“. So it can be discussed out in the open.
Science dies in the darkness.
The brief for the astrologers and soothsayers – no I’m kidding, future forecasters – in preparing a set of scenarios, later the four RCPs, was to produce internally consistent storylines that covered the range of CO2 concentrations (and other GHGs) covered in climate science papers.
From Emissions Scenarios, IPCC (2000):
..A set of scenarios was developed to represent the range of driving forces and emissions in the scenario literature so as to reflect current understanding and knowledge about underlying uncertainties. They exclude only outlying “surprise” or “disaster” scenarios in the literature. Any scenario necessarily includes subjective elements and is open to various interpretations. Preferences for the scenarios presented here vary among users. No judgment is offered in this Report as to the preference for any of the scenarios and they are not assigned probabilities of occurrence, neither must they be interpreted as policy recommendations..
[Emphasis added]
RCP8.5 was one of the four RCPs constructed because some simulations had covered quadrupling CO2 in the atmosphere (from pre-industrial levels). From van Vuuren et al (2011):
By design, the RCPs, as a set, cover the range of radiative forcing levels examined in the open literature and contain relevant information for climate model runs..
[Emphasis added]
Here are a few extracts from Riahi’s 2007 paper, which was the foundation for RCP8.5 in the 2011 paper (scenario A2r is similar to RCP8.5):
The task ahead of anticipating the possible developments over a time frame as ‘ridiculously’ long as a century is wrought with difficulties. Particularly, readers of this Journal will have sympathy for the difficulties in trying to capture social and technological changes over such a long time frame. One wonders how Arrhenius’ scenario of the world in 1996 would have looked, perhaps filled with just more of the same of his time—geopolitically, socially, and technologically. Would he have considered that 100 years later:
- backward and colonially exploited China would be in the process of surpassing the UK’s economic output, eventually even that of all of Europe or the USA?
- the existence of a highly productive economy within a social welfare state in his home country Sweden would elevate the rural and urban poor to unimaginable levels of personal affluence, consumption, and free time?
- the complete obsolescence of the dominant technology cluster of the day-coal-fired steam engines?
How he would have factored in the possibility of the emergence of new technologies, especially in view of Lord Kelvin’s sobering ‘conclusion’ of 1895 that “heavier-than-air flying machines are impossible”?
Also note that an “extremely high emissions scenario” (as I prefer to describe it), could also be constructed in other ways:
For reasons of scenario parsimony, our set of three scenarios does not include a scenario that combines high emissions (and hence high climate change) with low vulnerability (e.g., as reflected in high per capita incomes).
[Emphases added].
Here is the brief summary of the development of the A2 world – basically the RCP8.5 world:
The A2 storyline describes a very heterogeneous world. Fertility patterns across regions converge only slowly, which results in continuously increasing global population. The resulting ‘high population growth’ scenario adopted here is with 12 billion by 2100, lower than the original ‘high population’ SRES scenario A2 (15 billion). This reflects the most recent consensus of demographic projections toward lower future population levels as a result of a more rapid recent decline in the fertility levels of developing countries.
As in the A2 scenario, fertility patterns in our A2r scenario initially diverge as a result of an assumed delay in the demographic transition from high to low fertility levels in many developing countries. This delay could result both from a reorientation to traditional family values in the light of disappointed modernization expectations in this world of ‘fragmented regions’ and from economic pressures caused by low income per capita, in which large family size provides the only way of economic sustenance on the farm as well as in the city.
Only after an initial period of delay (to 2030) are fertility levels assumed to converge slowly, but they show persistent patterns of heterogeneity from high (some developing regions, such as Africa) to low (such as in Europe).
Economic development is primarily regionally oriented and per capita economic growth and technological change are more fragmented and slower than in other [scenarios]. Per capita GDP growth in our A2r scenario mirrors the theme of a ‘delayed fertility transition’ in terms that potentials for economic catch-up only become available once the demographic transition is re- assumed and a ‘demographic window of opportunity’ (favorable dependency ratios) opens (i.e., post-2030).
As a result, in this scenario, ‘the poor stay poor’ (at least initially) and per capita income growth is the lowest among the scenarios explored and converges only extremely slowly, both internationally and regionally. The combination of high population with limited per capita income growth yields large internal and international migratory pressures for the poor who seek economic opportunities. Given the regionally fragmented characteristic of the A2 world, it is assumed that international migration is tightly controlled through cultural, legal, and economic barriers. Therefore, migratory pressures are primarily expressed through internal migration into cities. Consequently, this scenario assumes the highest levels of urbanization rates and largest income disparities, both within cities (e.g., between affluent districts and destitute ‘favelas’) and between urban and rural areas.
Given the persistent heterogeneity in income levels and the large pressures to supply enough materials, energy, and food for a rapidly growing population, supply structures and prices of both commodities and services remain different across and within regions. This reflects differences in resource endowments, productivities, and regulatory priorities (e.g., for energy and food security).
The more limited rates of technological change that result from the slower rates of both productivity and economic growth (reducing R&D as well as capital turnover rates) translates into lower improvements in resource efficiency across all sectors. This leads to high energy, food, and natural resources demands, and a corresponding expansion of agricultural lands and deforestation.
The fragmented geopolitical nature of the scenario also results in a significant bottleneck for technology spillover effects and the international diffusion of advanced technologies. Energy supply is increasingly focused on low grade, regionally available resources (i.e., primarily coal), with post-fossil technologies (e.g., nuclear) only introduced in regions poorly endowed with resources.
[Emphases added]
Events that would prevent RCP8.5 occurring
- If sub-Saharan Africa stays mired in high levels of poverty – then it won’t be burning vast amounts of coal
- If sub-Saharan Africa moves out of high levels of poverty but goes through the “demographic transition” – women having less babies. This is something that has happened to every country so far, with cultures as different as Iran, Thailand and Taiwan – then the population won’t reach anything like 12bn and so it won’t be burning vast amounts of coal
- If sub-Saharan Africa moves out of high levels of poverty and doesn’t go through the “demographic transition” but adopts latest technology from more advanced countries, which is something that always happens especially with the internet, but also happened well before – then the energy efficiency of their economies will be much better than assumed
- If the above but for some reason sub-Saharan Africa doesn’t adopt more efficient technologies but the rest of the world makes lots of natural gas available at attractive prices – then not much coal will be burnt
It is a very unlikely world where RCP8.5 becomes a reality.
As a small backdrop, here are the population predictions from Wolfgang Lutz & Samir KC (2010). Lutz is a prolific figure in this field:
The total size of the world population is likely to increase from its current 7 billion to 8–10 billion by 2050. This uncertainty is because of unknown future fertility and mortality trends in different parts of the world. But the young age structure of the population and the fact that in much of Africa and Western Asia, fertility is still very high makes an increase by at least one more billion almost certain. Virtually, all the increase will happen in the developing world. For the second half of the century, population stabilization and the onset of a decline are likely.
[Emphasis added].
For people who don’t know much about development over the 20th century I very highly recommend The Great Escape, by Angus Deaton, Nobel Prize winner in Economics. He also covers the demographic transition.
Why This is Important
Some of the results of climate models for this “extremely high emissions scenario” (my term for it) contain very scary outcomes (I’ll be writing about climate models in this series).
The difference in outcomes (as predicted by models) between RCP8.5 and RCP6 (a more likely “business as usual” scenario) should be highlighted. If policymakers and the public are concerned that we might reach 12bn population in 2100 with sub-Saharan Africa lighting up coal fired power stations by the thousands then there are some straightforward steps to take.
- Keep the internet going so that technology for energy efficiency is available to sub-Saharan Africa, also teams of experts for technology transfer
- Encourage women’s education in that region (as Angus Deaton points out in his book this appears to be the key for the demographic transition)
- Encourage large scale gas extraction so that cheap gas is available instead of coal
I realise this last point goes against everything that climate activists believe in. But it seems like the rational response to the concern over RCP8.5 vs RCP6.
Surely this is why these scenarios were developed – so we can make some attempt to assess the outcomes and costs of different possible futures?
References
Scenarios of long-term socio-economic and environmental development under climate stabilization, Keywan Riahi et al, Technological Forecasting & Social Change 74 (2007)
RCP 8.5—A scenario of comparatively high greenhouse gas emissions, Keywan Riahi et al, Climatic Change (2011)
A special issue on the RCPs, van Vuuren et al (2011)
The Science of Doom 
[…] Update Jan 1, 2019 (Dec 31st, 2018 in some parts of the world) -just added Opinions and Perspectives – 3.5 – Follow up to “How much CO2 will there be?” due to […]
What if RCP8.5 becomes a reality in 2200 instead of 2100? Nothing magical about 2100. Suppose it takes a century longer to reach that milestone. What difference will that make in long-term warming? And to our descendants in 2500 AD?
In the meantime, feedbacks from melting permafrost and methane hydrates kick in, increasing GHG levels even if we stop.
Geoffrey,
A very important point.
I’m in favor of using the best available scientific evidence to inform policy. Rather than propaganda masquerading as science. I’m in a small minority I think.
I recommend reading A special issue on the RCPs, van Vuuren et al (2011) – free paper:
What they did was stabilize emissions so that the radiative forcing stayed at the prescribed level in each case. But this does allow looking at model results out to 2200 and 2300 with at least a flavor of that total level of emissions. The results won’t be the same as a slower emission of CO2, but the results at 2200 and 2300 will at least give an idea of what models think is the potential climate in 200-300 years.
Back to your point.
Do you think climate scientists should describe RCP8.5 as “business as usual” when it is instead a very unlikely scenario? Doesn’t matter if it “gets the job done”?
For me, I understand the value of propaganda. Most people don’t read IPCC reports, and even those that do, don’t get beyond the executive summaries which often are not executive summaries (I will write more about this in future articles).
So what becomes “accepted fact” is informed by press releases faithfully reported by stenographers. It’s an effective tool for crowd control.
But there is a catch to propaganda.
I think it will bring climate science into disrepute and that would be a tragedy.
So, my recommendation for climate science, just one irrelevant person, follow the points that you make in a consistent scientific rationale:
– consider honestly the difference between RCP6 and RCP8.5 and the implications of that for policy over the coming decades
– review the consequences of further emissions from 2100 to 2200 and 2300 and the possible future climates that might bring, and therefore the implications
– explain to policymakers
Geoffrey: Nic Lewis had a recent post TCRE at Climate Etc. that illuminated much about about the post 2100 future for me. TCRE is the transient temperature increase after society stops using so much fossil fuel because of regulation, taxation, or new technology takes over (possibly driven by shortages of fossil fuels). TCRE is 1.6 K/TtC (0.8-2.4) in the IPCC’s models and 1.05 KTtC according to Nic’s estimates from energy balance models (observations of warming and forcing). However, there is also a second, under-publicized concept called ECRE, the EQUILIBRIUM warming after emitted CO2 has equilibrated among all reservoirs.
At equilibrium pre-industrially, we had something like 0.6, 2.1 and 3.9 TtC – about 1.4% in the air, land and ocean. What happens when we add another 2 TtC to the system? To a first approximation, it will distribute at equilibrium in the same ratio as it did pre-industrially. However, acidification and warming means that the ocean will hold less CO2 at equilibrium than it did before, a problem addressed by the “Revelle factor”. If I remember correctly, the Revelle factor means that new CO2 will eventually be distributed about 1:10 between air and ocean (rather than at the current ratio of 0.15:10).
So far, we have emitted about 0.75 TtC, and about 50% of those emissions remain in the air. In other words, we are very far from equilibrium!
How long does it take to approach equilibrium? It takes about a millennium for the deep ocean to mix with surface water. The same mixing process is responsible for the lag between current warming (TCR) and equilibrium warming (ECS), aka “committed warming”. So, whenever CO2 emissions slow substantially, committed warming may be counterbalanced by redistribution of CO2 into the deep ocean. In the long run, redistribution wins. According to Nic’s calculations, ECRE is about half of TCRE or 0.5 K/TtC. The IPCC hasn’t offered an estimate for ECRE.
https://judithcurry.com/2018/12/11/climate-sensitivity-to-cumulative-carbon-emissions/#more-24552
Goodwin, P. et al, 2007: Ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales. Global Biogeochem. Cycles, 21, GB1014, doi:10.1029/2006GB002810.
My guess is that your descendants in 2500 will be cooler than your descendants in 2300. The IPCC’s view about this subject admits this is possible, but their central estimate is they will be equally hot.
https://curryja.files.wordpress.com/2018/12/froelicher2015_fig2a.png?w=768&h=612
Except that the TCRE contains a statistics bug
https://tambonthongchai.com/2018/05/06/tcre/
https://tambonthongchai.com/2018/12/03/tcruparody/
When the bug is fixed the proportionality goes away
https://tambonthongchai.com/2018/12/14/climateaction/
Geoff, At some point predictions about the future become very unreliable. I would say we have no idea what energy technology will look like in 2100, much less in 2500. We can’t even predict the next recession.
dpy6629: The uncertainty in total emissions in the future is large. However, we can be confident that the current airborne fraction will eventually drop from about 50% to below 20%
The Revelle factor is the ratio of the change in atmospheric [dCO2] to pre-industriaI CO2 [CO2]_PI = 0.575 TtC, divided by the ratio of the change in dissolved inorganic carbon [dDIC] to pre-industrial dissolved inorganic carbon [DIC]_PI = 38 TtC. The current Revelle Factor is 10 and will rise to around 12-14 depends on emissions. We have emitted about 0.55 TtC of CO2 and about 50% remains in the air right now (410 ppm), but after equilibration that will drop to 14% airborne fraction (about 320 ppm). By the time we have tripled our total emissions and then reached equilibrium, there will be about 410 ppm of CO2. And this is without considering any change in land reservoirs or the very slow precipitation of CaCO3. (Assuming my calculations are correct.)
See: Goodwin, P. et al, 2007: Ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales. Global Biogeochem. Cycles, 21, GB1014, doi:10.1029/2006GB002810. http://ocean.mit.edu/~stephd/2006GB002810.pdf
So, however bad things get, over centuries things will get better. The GIS survived 2 millennia of the Holocene Climate Optimum. Antarctica isn’t likely to melt before CO2 redistributes into the deep ocean, but some fraction of West Antarctica appears vulnerable.
An interesting discussion but I feel so much concentration on science and numbers misses the point. A scenario is not intended to be a forecast.
Long ago when I was an undergraduate studying physics, we thought of a hydrogen molecule as chemistry. Fortunately much has changed for the better since then and atmospheric and earth sciences have benefited vastly. There is now a need for climate scientists to broaden their perspective even further and embrace the social sciences and I try to encourage the scientists to learn some economics. Sadly this is not accepted by most who claim they don’t have time although there is the odd exception. In their turn quite a lot of social scientists working on climate tend to have too much faith in the accuracy of climate forecasts.
The uncertainty in the Kaya factors has been discussed, but at the end of the day there is much uncertainty in many broader areas, such as the land and land use. This is on top of the uncertainties in the climate forecasts. Yes we can be confident that quantum mechanics and the first law of thermodynamics make warming certain unless something totally unforeseen is happening. So I would conclude that the climate science is subject to less uncertainty than the economic and behavioural forces. However, both of these are fairly trivial compared with the political response. Here the progress to me seems mercurial. Hence I am more than happy with the ‘business as usual’ label.
We are all humans so subject to psychological pressure to conform to the thinking of our group so no doubt climate scientists started from the position of quite liking warming. But because of attacks that they had been too pessimistic there have been suggestions that with AR5 they downplayed lower probability more catastrophic scenarios. As for the rest of us, we seem to be fixed on a path of unlimited delay, and take a short term view like most of our politicians.
In spite of this, I remain optimistic. Renewable prices have been dropping faster than expected, China is worried about pollution and the likes of Blackrock are moving in the right direction. On the other hand Europe as it deindustrializes ignores embedded emissions in its targets, there is Trump and in practice too little has been achieved in over two decades since COP1. The optimism of Paris was based on the assumption that once we had reached net zero, we would later remove carbon from the atmosphere – using technology that does not exist.
But rather than worry about the label on a scenario I suggest we should worry about the lack of political progress. Understanding and balancing all the details is beyond me, but I would recommend people follow David Victor who gives his views in this brief lecture:
John, its a thoughtful comment. I think there a number of causes of lack of political “progress.”
1. Mitigation is costly and harms the interests of ordinary people like the yellow vests. In democracies, these people still have a say even though many elites wish that was not the case.
2. There is a very powerful ideological preference among the green for wind and solar over more practical things like nuclear or switching to natural gas. These biases make workable responses (that would have bipartisan support) difficult. Without clean electric energy, transport will never become cleaner.
3. Finally I think ordinary people are sick and tired of experts telling them what to eat, how to get to work, where to live, and how we need to make energy more expensive. These feelings are amply justified by the increasingly common failures of science and its public policy implementations. A recent and big one was the dietary fat fiasco which has lasted at least 50 years, which probably has harmed the health of millions.
4. We live in an age of media propaganda financed by billionaires with no strong commitment to truth, but strong partisan emotions about the evildoers they are opposing. The atmosphere is full of misinformation and there are political advocacy groups trying to counter it with more misinformation. Scientists are participating in this flood of misinformation by encouraging the attribution of every extreme event to global warming and also with their dishonest press releases. Resplandy et al is a prime example. The press release led to a flood of false press reports. This is a primary cause of public crisis fatigue.
Perhaps scientists needs to step back and try to find common ground with those they disagree with and stop trying to marginalize them and calling them names. Better policing of their own ranks to stop the constant exaggerations and push back against the more extreme climate warriors might help. You will see in this comment thread a discussion of Hansen’s 1988 Congressional testimony. It is very hard to argue it was not an unrealistic worst case propagated as “business as usual.”
The public will perhaps come to trust experts when the experts become trustworthy. In any case, truth and acknowledgement of uncertainty is the only way to advance human knowledge.
An example of how this could work might be the FAA and commercial aviation. The processes are quite transparent and political partisanship nonexistent and there is constant self-criticism. As air travel has become amazingly safe, the public gains high confidence in airframe manufacturers and the FAA.
A comparison of RCP8.5 with observational data
https://tambonthongchai.com/2018/09/08/climate-change-theory-vs-data/
John Peaars and dpy make thoughtful comments, but don’t completely address Riahl’s 2007 paper and the difficulties of predicting, even imagining future social and technological changes. John promotes the precautionary principle and bemoans the fact of so little mitigation progress. And dpy offers several economic, political, and psychological reasons for the lack of progress- all good points.
The major underlying reason for the for the ubiquitous acceptance of the RCP8.5 scenario, I submit, is something else, not even related to our best climate science, economic, and demographic model predictions, inadequate as any such models are. The main reason is the pessimism and unsupported belief that everything is getting worse. With the belief in dystopian trends, is it any wonder that catastrophic warming and the RCP8.5 are promoted?
The reason for such pessimism are complex, but the pessimism is certainly fueled by ignorance of history.
Countering this ignorance and pessimism are Hans Rosling very funny and very serious Ted Talk, “How Not To Be Ignorant About the World” https://www.youtube.com/watch?v=Sm5xF-UYgdg
and Steven Pinker’s best selling book, “Enlightenment Now.”
Yes Doug, I do agree that there is a general unsupported belief in the West that everything is getting worse despite continued increases in most measures of well-being. Pollution is dramatically lower than only 40 years ago. Life expectancy is higher, medicine continues to advance, etc. Two years ago I had cataract surgery and within 24 hours my vision was better than at any time over the last 30 years. 100 years ago, I would be almost blind by now.
A lot of this has to do with a cultural crisis in the West. Faith in progress was one of the great hallmarks of the Enlightenment. Romanticism and Rousseau hated progress and claimed it was not progress. Romanticism’s descendants now dominate the West according to Bertrand Russell’s History of Western Philosophy.
Many of our current problems such as the opiod epidemic are cultural problems.
Yes, dpy! Although I think Science of Doom is the most thoughtfully critical blog on climate science and recommend it to my climate science students, its author mostly considers science as it ideally should be considered, on its own merits. This is not criticism of SOD. Instead, it’s exactly what climate science needs. However, from a more comprehensive view, I see science and scientific method as vessels floating on the turbulent seas of cultural, philosophic, and political thought/ ideological conflict.
Steven Pinker, author of “Enlightnment Now” and participant in the conflict, shows how we humans are flourishing in virtually every respect , and have always been resourceful in solving problems or managing those without solutions. He defends enlightenment values in a recent essay I recommend- https://quillette.com/2019/01/14/enlightenment-wars-some-reflections-on-enlightenment-now-one-year-later/
Hi,
What key climate scientists should do is publish a paper “Why RCP8.5 is actually business as usual“.
Why (or indeed, how?) would anyone publish such a paper when the scientific literature already states that RCP8.5 is business as usual? What’s notable is that those attempting to discredit RCP8.5 as business as usual have not done so through the scientific literature, instead choosing to run attack pieces on social media and blogs/op-eds.
RCP8.5 was one of the four RCPs constructed because some simulations had covered quadrupling CO2 in the atmosphere
This is simply false. RCP8.5 was one of the RCPs because it was in the range of forecasts produced by storyline-based economic modelling. In rounds of such modelling over the past few decades scenarios with RCP8.5 level emissions have repeatedly come out as a plausible no-mitigation future. A1FI was one in the SRES, and SSP5 is one in the new SSPs.
Events that would prevent RCP8.5 occurring…
That is just hand waving. No numbers, no modelling. And the modelling has already been done. Your first scenario there is basically Riahi 2011 RCP8.5: low economic growth, high population growth, Your second scenario is basically A1FI/SSP5: High economic growth, low population growth. Perfectly plausible that they can produce RCP8.5 level emissions.
As a small backdrop, here are the population predictions
I really don’t understand why I need to repeat this over and over again: high population growth is not required for RCP8.5 level emissions. A1FI and SSP5 both have 2100 population at 7 billion i.e. lower than today.
The difference in outcomes (as predicted by models) between RCP8.5 and RCP6 (a more likely “business as usual” scenario) should be highlighted.
I’m glad that you’ve put them together as both business as usual scenarios now, but I would really like to see how you can justify a claim that RCP6 is more likely. In economic modelling under the no-mitigation assumption, an RCP6 pathway is actually equally as “extreme” a possibility at the low end as RCP8.5 is at the high end.
In fact the observed CO2 growth rate is already about 25% higher than in the CMIP5 RCP6 scenario, and no acceleration happens in RCP6 CO2 growth rate for a couple of decades. The current observed growth rate is only reached in the 2040s. Now, there are other ways to get to RCP6 but what this demonstrates is that following RCP6 requires a sharp move away from the observed acceleration of emissions.
Surely this is why these scenarios were developed – so we can make some attempt to assess the outcomes and costs of different possible futures?
Absolutely. Which is why it’s a terrible idea to artificially ignore certain possible futures before you even get to question of what to do.
Encourage large scale gas extraction so that cheap gas is available instead of coal
That would be a mitigation policy of course. Though, as I mentioned on the other thread, not a very good one and would probably be better named a “delaying policy”. And not delaying for very long. I’ve done some modelling to put some numbers to that:
Taking the oil, gas and coal energy consumption figures from SSP5, obtaining a conversion coefficient for each to carbon emissions, then converting to CO2 concentration growth using the CMIP5 RCP8.5 airborne fraction coefficient and adding in the CMIP5 RCP8.5 land use emissions I produced an SSP5 CO2 forecast. The result is a 2100 CO2 concentration of 956ppm (note that this, presumably, does not include cement emissions so probably a small underestimate).
I then, from 2018, model a total transition from coal to gas over a decade. Meaning by 2028 there is zero coal consumption and all energy produced by coal in SSP5 is instead produced via gas. Because airborne fraction has some dependency on emission magnitude, and the resulting coal-gas transition SSP5 has emissions about midway between CMIP5 RCP6 and RCP8.5 I adopt the average airborne fraction for the two CMIP5 scenarios to produce CO2 concentration growth. The result is a 2100 concentration of 789ppm. Well above RCP6. Furthermore, the growth rate at end of century is just shy of 6ppm/year so CMIP5 RCP8.5 level 2100 concentration is reached at 2126 (again, note no cement emissions in the SSP5 reconstruction) and SSP5 2100 concentration is reached in 2129. It’s just a deferment, not a solution.
A1F1 isn’t BAU either.
You mean the scientific literature asserts that RCP8.5 is BAU. That’s not evidence.
A1F1 isn’t BAU either.
Yes, it is.
The scientific literature en masse unanimously asserting something certainly is evidence of who has the onus to publish on a disagreement.
To be honest, this part is getting a bit silly now. It’s not like ‘BaU’ is some fundamental property of the universe and we’re trying to find a correct objective parameter value. It’s a phrase imbued with what is essentially an arbitrary definition. Yet there is a standard one in the climate/policy field which has been accepted for decades. By this standard definition RCP8.5 is business as usual. There really is no question about this and it’s why RCP8.5 is referenced as BaU in hundreds, maybe thousands of papers in the scientific literature. Also why A1FI is referenced as same.
It’s pretty clear that those asserting that it isn’t BaU must be operating with an alternative definition, which is fine. Just don’t expect everyone else to share it.
paulski0,
You’ll have to humor us dummies a little bit.
We have some wild ideas on this blog. One of them is that lots of important and smart people repeating something counts as zero evidence.
What paper actually makes the case that quadrupling CO2 by 2100 is a likely outcome based on current human activity and continuing past trends?
We have some wild ideas on this blog. One of them is that lots of important and smart people repeating something counts as zero evidence.
What is it you think I’ve claimed it as evidence of?
What paper actually makes the case that quadrupling CO2 by 2100 is a likely outcome based on current human activity and continuing past trends?
Firstly, none of the RCP8.5 scenarios discussed feature CO2 quadrupling by 2100. SSP5 apparently comes close, based on the ScenarioMIP paper from 2016, at about 1080ppm, though I don’t know if that’s finalised. A1FI gets to about 960ppm, Riahi2011 RCP8.5 gets to about 940ppm.
But also, has anybody argued that it’s a likely outcome? Plausible, yes. Likely, not necessarily.
In terms of assigning probabilities to no-mitigation scenarios the question is how would you go about assessing such a thing? Essentially futurology – trying to predict where developments take us in future. One approach could be to take our understanding of economics, devise some plausible scenarios and look at the range of outcomes produced. For example, the recent Shared Socioeconomic Pathways program, the development of the CMIP5 RCPs, that time from the independent scenario literature and, of course, the SRES. All of those produced a scenario at around RCP8.5 level, demonstrating that it is a plausible scenario. Though it’s not clear whether you can reasonably infer probabilities from these scenario ranges.
For another approach, Christensen et al. 2018 used an econometric method for analysing trends and found large uncertainty, suggesting a >35% chance of concentrations exceeding RCP8.5.
Richard Tol also performed an analysis on the SRES scenarios in the lead up to AR4, not sure he ever published. It’s discussed in the minutes of a meeting which used to be available from this url, but the link is now broken by the new ipcc site architecture. In a multi-variate comparison with historical trends he found that the A2 scenario ‘is by far the most probable’.
All of this work points to RCP8.5 being a plausible pathway worth consideration.
Atmospheric CO2 growth rate has been 0,5% pr year the last decades. This has been a very stable growth.
February 23, 2019: 410.81 ppm.
This will give 615 ppm CO2 in year 2100.
This is the most reasonable way to see Business as Usual.
Correction.
From 1958 (the whole Mauna Loa period) the growth rate is 0,44%.
So Business as Usual gives 588 ppm CO2 in year 2100.
RCP8.5 = RealClimatePhantasyOf8.5degFarenheitThisCentury.
Or as our friend Andy tells us about Business as Usual: “If we don’t take action, unchecked greenhouse-gas emissions would lead to global-average warming over this century of 5 degrees Fahrenheit to 9 degrees Fahrenheit.”
“This warming is as certain as death and taxes. And if that wasn’t enough, there is a long list of other worrying impacts that flow from it. Warming has already made heat waves more frequent and intense, and it will only get worse. Climate change has already intensified rainfall patterns, turbocharging events like Hurricane Harvey. As oceans warm and glaciers and ice sheets melt, our seas rise, leading to enhanced coastal flooding. And excess carbon dioxide in the air is absorbed by the oceans, gradually but steadily turning them more acidic, which is bad news for the ocean’s ecosystems.”
I think this kind of science fiction is a result of taking RCPs too serious.
“RCP8.5 = RealClimatePhantasyOf8.5degFarenheitThisCentury.”
Nobody,
You have misunderstood RCPs.
The 8.5 does not refer to a temperature increase in “Farenheit” [sic].
It refers to a forcing of 8.5 W/m2.
nobodysknowledge,
This has been covered already. The growth rate has not been at all stable. It was under 0.3% at the beginning of the Mauna Loa record. It’s now over 0.6%, with a steady upward trend in between. As a further illustration, the most recent individual year which did not exceed your 0.44% growth rate was 2001.
Extrapolating using the linear acceleration of growth rate in the Mauna Loa record produces 2100 CO2 of 816ppm. RCP8.5 level CO2 is reached by 2115.
I admit hat I have made an inaccurate estimate of trend. But I would correct for the part of CO2 increase that is feedback of Ocean warming (0 to 700 m) since 1955. Then I think the growth rate of 0,44% pr year is very close to a real trend. So I think your extrapolation is dependent on a great OHC accelleration, which seems very unlikely.
Paulski, NK and VTG: Extrapolating a rise in CO2 from recent trends is dubious, because many changing factors influence that trend: population growth (and fall?), GDP/capita, energy consumed/$GDP, and CO2/energy. Theses factors are different for different countries and are going to change.
Yes Frank, extrapolation is wild speculation. But I cannot see that there is a better way to make a Business as Usual estimate. It will always be wild speculation, made out of ignorance.
NK: There are a lot of factors that contribute to the terms in the above Kaya identity. For me, BAU means that we determine what BAU means for each of those factors.
Above, I think we have talked about the factors that have brought much of the world to zero population growth or below. BAU means continuing to apply those factors.
I was recently curious about the debate between believers in secular stagnation and those who think the latest US tax cuts are going to make 3 or 4% real GDP growth the new normal. From my limited reading about “total factor productivity”, after correcting for growth in the number of workers (population growth times labor force partition rate), GDP/worker in good times has grown about 0.4%/year due to an increasingly educated and more productive work force and 1.5%/year due to investment in productivity. Education is reaching a plateau. Business investment in productivity as a % of GDP has remained fairly constant for a half-century. For me, BAU would mean continuing these trends and not endorsing either secular stagnation (apparently an old idea that appeared after previous deep recessions and depressions) or massive increase in business investment that would dramatically increase productivity. In truth, my understanding of macroeconomics is poor at best, but BAU for GDP/capita should be based on such information.
So, BAU for CO2 emissions should be based on current trends and understanding of many factors, not simple extrapolation of the current rate of CO2 increase. Speculation about secular stagnation or a massive increase in investment in productivity would not be BAU. For the US (with 0.5%/yr increase in workers for the next decade), BAU appears to be 2% real GDP growth.
Zeke Hausfather explains in https://www.carbonbrief.org/explainer-the-high-emissions-rcp8-5-global-warming-scenario
One extract:
The creators of RCP8.5 had not intended it to represent the most likely “business as usual” outcome, emphasising that “no likelihood or preference is attached” to any of the specific scenarios. Its subsequent use as such represents something of a breakdown in communication between energy systems modellers and the climate modelling community.
Whilst the uncertainty is huge in any of these exercises, it’s perhaps worth looking at the range of outcomes in a no-mitigation policy world.
That seems to be 6-8.5 W/m2 from the referenced article, with 7.0 perhaps mos likely.
From the article:
I would note that the difference between 8.5 and 7.0 is pretty small compared to all the other uncertainties in projecting future climate (ECS range typically quoted 1.5-4.5).
vtg,
In a word, no.
The difference between 8.5 (SSP5) and 7.0 (SSP3) is indeed quite large, but not until after 2030 or so. But then all the scenarios except SSP1 (RCP 1.9) don’t diverge much until after 2020. And SSP3 is also considered unlikely. And we are currently projected to be well below SSP3 and SSP5 emissions and even slightly below SSP4 (RCP 6.0) by 2040. So BAU may actually be closer to SSP2 (RCP 4.5) than SSP4.
Nature magazine has published a comment from Zeke Hausfather and Glen Peters that agrees with what SOD has written here and what Zeke wrote in the blog post linked above. Publication in Nature suggests that Zeke’s and SOD’s blog posts are within the “consensus”.
Title: Emissions – the ‘business as usual’ story is misleading.
Subtitle: “Stop using the worst-case scenario for climate warming as the most likely outcome — more-realistic baselines make for better policy.”
https://www.nature.com/articles/d41586-020-00177-3
“More than a decade ago, climate scientists and energy modellers made a choice about how to describe the effects of emissions on Earth’s future climate. That choice has had unintended consequences which today are hotly debated. With the Sixth Assessment Report (AR6) from the Intergovernmental Panel on Climate Change (IPCC) moving into its final stages in 2020, there is now a rare opportunity to reboot.”
“RCP8.5 was intended to explore an unlikely high-risk future [Ref 2]. But it has been widely used by some experts, policymakers and the media as something else entirely: as a likely ‘business as usual’ outcome. A sizeable portion of the literature on climate impacts refers to RCP8.5 as business as usual, implying that it is probable in the absence of stringent climate mitigation. The media then often amplifies this message, sometimes without communicating the nuances. This results in further confusion regarding probable emissions outcomes, because many climate researchers are not familiar with the details of these scenarios in the energy-modelling literature.”
Reference 2: https://link.springer.com/article/10.1007/s10584-011-0149-y
From abstract: “This paper summarizes the main characteristics of the RCP8.5 scenario. The RCP8.5 combines assumptions about high population and relatively slow income growth with modest rates of technological change and energy intensity improvements, leading in the long term to high energy demand and GHG emissions in absence of climate change policies.”
The Hausfather Nature Comment linked above prompted me to read about and share the new terminology AR6 will be using that combines SSP’s = Shared Socioeconomic Pathways with RCP’s (1.9, 2.6, 3.4, 4.5, 6.0, 7.0 or 8.5 W/m2 of radiative forcing in 2100). According to Zeke:
“Finally, we suggest that climate-impact studies using models developed for AR6 should include scenarios that reflect more-plausible outcomes, such as SSP2-4.5, SSP4-6.0 and SSP3-7.0 (see ’Possible futures’). When RCP8.5 or its successor SSP5-8.5 are deployed, they should be clearly labelled as unlikely worst cases rather than as business as usual.”
The new (and old) RCPs are reviewed by O’Neill et al (2016): https://www.geosci-model-dev.net/9/3461/2016/gmd-9-3461-2016.pdf
” “Gap scenarios”: new forcing pathways not covered by the RCPs, including new unmitigated SSP baseline scenarios and new mitigation pathways. Pathways identified of special interest, as discussed further below, were those reaching 7.0, 3.4, and below 2.6 W/m2 in 2100 (the latter explicitly to inform understanding of the 1.5 C goal in the Paris agreement). The 7.0 W/m2 pathway represents an UNMITIGATED baseline scenario, whereas the 3.4 and <2.6 W/m2 pathways are new mitigation scenarios."
The five Shared Socioeconomic Pathways mentioned by Zeke are described in https://www.sciencedirect.com/science/article/pii/S0959378016300681 Each SSP comes with an unmitigated baseline scenario and a range of mitigation possibilities. I've added in brackets the RCP's that could result from each of these SSPs assuming different amounts of mitigation according to Figure 2 of O'Neill (2016). Even the pathway based on "fossil fuel development" has a RCP 2.6 W/m2 endpoint that assumes widespread adoption of carbon capture technology. There are 26 possible combinations of SSPs and RCPs in Figure 2, with 4 "Tier 1 Scenarios" (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) given top priority for modeling and 5 additional "Tier 2 Scenarios". As best I can tell, SSP5-8.5 should be labeled "worst-case scenario" and SSP3-7.0 should be labeled "business as usual'. I'd like to have a scenario called "mitigation-as-usual" that represents the uneven modest mitigation that is already underway in developed countries that should become less costly and adopted by developing countries as they become more prosperous. Unfortunately RCP6.0 assumed no mitigation until mid-century and and we are already more than halfway to RCP4.5 today and emissions are still rising. "Mitigation-as-usual" seems to be somewhere between 4.5 and 6.0 W/m2.
"SSP1 Sustainability – Taking the Green Road (Low challenges to mitigation and adaptation) [RCPs 1.9-6.0 W/m2] The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity.
SSP2 Middle of the Road – (Medium challenges to mitigation and adaptation) [RCPs 1.9-7.0 W/m2] The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain.
SSP3 Regional Rivalry – A Rocky Road (High challenges to mitigation and adaptation) [RCPs 3.4-7.0 W/m2] A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions.
SSP4 Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation) [RCPs 2.6-6.0 W/m2] Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas.
SSP5 Fossil-fueled Development – Taking the Highway (High challenges to mitigation, low challenges to adaptation) [RCPs 2.6-8.5 W/m2] This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital as the path to sustainable development. Global markets are increasingly integrated. There are also strong investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social development is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy intensive lifestyles around the world. All these factors lead to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local environmental problems like air pollution are successfully managed. There is faith in the ability to effectively manage social and ecological systems, including by geo-engineering if necessary."
After posting information on the new combinations of SSPs and RCP that presumably will be used by AR6, I decided that the “Possible Futures” Figure from Hausfather and Peters is vastly more informative. I’ll try to post that Figure below:
https://www.nature.com/articles/d41586-020-00177-3
[…] rcp 8.5 – extreme CO2 emissions, often misleadingly cited as “business as usual” (see Opinions and Perspectives – 3 – How much CO2 will there be? And Activists in Disguise and Opinions and Perspectives – 3.5 – Follow up to “How much CO2 will there be?”) […]