For some time now I have been wanting to write a piece on something called RCP8.5, which is a scenario about what might happen to humanity in the 21st century and the effects it might have on the various indicators of ‘climate change’ — temperature, sea-levels, precipitation and the like. The RCP8.5 climatic world is dire, and many of the AGW scare stories (for example, herehere, and here) are built on the supposition that it is going to happen. Another article, published very recently, has pushed me to do delve further into RCP8.5. Written by Pat Michaels and David Wojick, both of whom seem to me to be sensible people, given what I have seen of their earlier contributions, the article points to the astonishing amount of climate science that is based on computer models.

A couple of statistics make the point eloquently. The authors searched Google Scholar for articles that used terms related to modelling, and it turned out that about half of all the papers were in climate science, broadly defined. But climate science is only about 4 per cent of all natural science. When they looked at climate science itself, the magical 97 per cent figure emerged at once: that is the proportion of all articles in climate science that also used the term  ‘model,’ ‘modelled’ or ‘modelling’. The subsequent comments to the article include some that dispute the methodology the authors used, and argue for a smaller figure. It would still be very large, it seems to me, and it is really quite rare to find a paper in climate science that is only about observations.

Now to  RCP8.5, which stands for Representative Concentration Pathway 8.5. What does that mean? Well, the IPCC devised these Pathways for its last report. There are four of them, and they offer climate futures that are thought to be both possible and to depend on how much greenhouse gas  is emitted hereafter (hence ‘concentration’). The number refers to the increase in radiative forcing values in 2100, so RCP8.5 offers an increase of 8.5 Watts per square metre by 2100. That is quite a lot. Other values are +2.6, +4.5 and +6.0.

How do we get to there? Well, you can read all about RCP8.5 here. It is a model, based on a scenario and ‘storyline’ that go like this.

The scenario’s storyline describes a heterogeneous world with continuously increasing global population, resulting in a global population of 12 billion by 2100. Per capita income growth is slow and both internationally as well as regionally there is only little convergence between high and low income countries. Global GDP reaches around 250 trillion US2005$ in 2100. The slow economic development also implies little progress in terms of efficiency. Combined with the high population growth, this leads to high energy demands. Still, international trade in energy and technology is limited and overall rates of technological progress is modest. The inherent emphasis on greater self-sufficiency of individual countries and regions assumed in the scenario implies a reliance on domestically available resources. Resource availability is not necessarily a constraint but easily accessible conventional oil and gas become relatively scarce in comparison to more difficult to harvest unconventional fuels like tar sands or oil shale. Given the overall slow rate of technological improvements in low-carbon technologies, the future energy system moves toward coal-intensive technology choices with high GHG emissions. Environmental concerns in the A2 world are locally strong, especially in high and medium income regions. Food security is also a major concern, especially in low-income regions and agricultural productivity increases to feed a steadily increasing population.

It doesn’t sound an attractive world, does it. But how likely is it? One sixth of the present century has already passed. So it’s worth looking at the ingredients of the storyline and inspect what is happening to them. Let’s start with the 12 billion human population for 2100. There are several different estimates of world population over the century, and you can see them here. We can be reasonably confident about what will happen in the next thirty years, because we know a good deal about the fertility of the current 7 billion or so of us. A best guess for mid-century is around 9 billion, given that fertility rates are dropping everywhere, even in sub-Saharan Africa. It might even be lower. But unless there is some kind of cultural change that makes larger families attractive and contraception unpopular, it is hard to see that 12 billion figure as part of the future. Indeed, male contraception is apparently close.

OK, what about low economic growth and no real closing of the gap between rich and poor countries? Once again, we have to deal with another model. PWC has prepared a projection of economic growth to 2015, its model  based on projected trends in demographics, capital investment, education levels and technological progress. Beyond 2050 (and I would say, even before that) we are dealing with so many variables that what comes out of the model is little more than guesses based on what the modellers put in. But the short story is simple: the world economy is expected to grow at about 3 per cent per annum, doubling in size by 2037 and trebling a little after 2050. And the economic power shift from the USA, Japan and Northern Europe will continue, with developing countries growing their economies quickly, and raising their standards of living.

Any signs of technological development slowing down? Not really. As I wrote the other day, we are in the midst of a technological change that is changing the way we work, and the sorts of jobs we have. What would stabilise things? The expansion of knowledge since the Second World War has been enormous, and shows no signs of stopping. Challenges produce responses. My guess is that any attempt to halt technological change in country X, for whatever apparently good reason, would simply allow other countries to bypass it. No, I do not know where it will all end, and won’t live to see it. But you can read a useful summary of the debate about accelerating change here.

What’s left of RPC8.5? The use of fuels. I have written before, a few times, that in the long run a good deal of our energy needs will be met by solar energy, once storage has been solved at the grid level. Or, solar energy may be bypassed by new developments elsewhere. Wind is simply a terrible waste of money and time, save where there is no real alternative at all. Although coal is still the main producer of electrical energy, its share is declining as natural gas and cheap oil take its place. We may see nuclear energy enjoy a renaissance, too. All in all, the RCP8.5 projection that the world will move to coal-intensive energy production seems most unlikely to me. Food production has been growing steadily for the past thirty years, helped by increasing CO2. Why is that to cease?

All in all, the probability that RCP8.5 is a real picture of our global future seems fantastic to me, since its assumptions all seem wrong or highly unlikely. Why then bother with it? Because so many AGW scare stories start with it. No reader is likely to know what RCP8.5 means, which is why I thought it worth writing about. Now that I have done so, I feel that newspapers and other media that broadcast such scare stories without mentioning that they are based on a most unlikely prospect seem to me to behave in an unethical and almost fraudulent way.

End-note: RCP8.5 is sometimes also called the ‘business as usual’ pathway, or ‘BAU’. Perhaps those who use that term mean simply that no one in that pathway is concerned about greenhouse gas emissions (which is part of the assumption). But business as usual is certainly not what describes that scenario. Businessmen adapt or their companies go under. Businessmen search for new ways to do things better. RCP8.5 envisages a world of economic stagnation. I can’t see why you would call that ‘business as usual’.

Later: Here’s another similar scary story, from Nature.

Join the discussion 23 Comments

  • Neville says:

    The idea that anyone would trust their projections to 2100 is ridiculous. Just look at the COP 21 forecast that has been blown out of the water in just 5 months. The EIA ( Obama govt) has just produced their forecast for the planet out to 2040. Co2 emissions will increase by 34% over the next 25 years and the majority of that increase will be emitted by non OECD countries.( China, India etc.) Here is page 3 of their May 2016 report. Dr Hansen was correct, COP21 was BS and a fraud.

    Key findings in the IEO2016 Reference case (continued)

    “Among the fossil fuels, natural gas grows the fastest. Coal use plateaus in the mid-term as China shifts from energy-intensive industries to services and worldwide policies to limit coal use intensify. By 2030, natural gas surpasses coal as the world’s second largest energy source.

    In 2012, coal provided 40% of the world’s total net electricity generation. By 2040, coal, natural gas, and renewable energy sources provide roughly equal shares (28-29%) of world generation.

    With current policies and regulations, worldwide energy-related carbon dioxide emissions rise from about 32 billion metric tons in 2012 to 36 billion metric tons in 2020 and then to 43 billion metric tons in 2040, a 34% increase.”

    Here is the full report.

  • Peter Kemmis says:

    It seems to me that we have been continuing to run using a “business as usual” template for many decades, including since 1988, the Year of James Hansen. So now, we are in the year 28 JH, and apart from a contribution from wind and solar generation of 2% of our global energy needs, with carbon dioxide levels steadily rising, relatively stable atmospheric temperatures, and no acceleration in sea level rises. Meanwhile, despite the impact of the GFC, economies stutter along, global trade increases and technology advances. Sure, there are may hiccoughs along the way, but it seems more likely that economies and technology will follow their templates of the last few decades.

    The population forecast of RCP8.5 is at odds with other forecasts; the latter take into account the impact of rising living standards that lead to lower birth rates. Forecasts I have seen suggest that world population might peak at around 9 billion.

    What is sadly ironic is that cheap energy from fossil fuels is critical to lifting those living standards, but policies which seek to close down those avenues encourage the very outcome decried in the scenario above, a global population of 12 billion.

    Apart from the scenario being so inconsistent with the trajectory of the last few decades, the glaring omission is the potential use of far more nuclear energy. Ironic that the greatest cost of Hiroshima and Nagasaki, horrific as it was for its victims and for Japan, has been on the succeeding generations of the very poor across the world. We became irrationally afraid of nuclear power, subconsciously associating it with thumping great explosions and far-reaching radiation. I remember reading Nevil Shute’s “On the Beach” shortly after its release in 1957, and the images he described seemed very possible back then. (A movie was made some decade later, I recall.)

    Maybe the code name of RCP8.5 should be re-assigned, perhaps to a contra-pill such as RU-486. Or perhaps the latter could be used to treat the former.

  • margaret says:

    Harry Lime:
    “Would you feel any pity if one of those dots stopped moving forever?
    If I offered you £20,000 for every dot that stopped – would you really, old man, tell me to keep my money? Or would you calculate how many dots you could afford to spare? Free of income tax, old man……free of income tax.
    It’s the only way to save money nowadays.”

    • Peter Kemmis says:

      Margaret, your quotation is thoughtful and relevant. Harry describes what one might call the “indifference to anonymity”. I do not think you are arguing that each dot does not matter – nor was Harry. He was bringing it to the personal level, and in that sense, for each of us, no matter where we sit on the population or climate or refugee divides, the anonymous remain so, as do our levels of indifference. But it does matter to each individual “anonymous” person, and we should make policy with that understanding, knowing full well that it will never be perfect, and often the deserving suffer the fate that should be that of the undeserving.

      So what is the inference you wish us to draw? That to a climate sceptic, the anonymous dot does not matter? Or that to a refugee advocate, the anonymous refugee in a camp does not matter, but the one whose face and form we see on a smuggler’s boat, is one who matters more, because no longer anonymous? You have left me a little puzzled.

      • margaret says:

        Harry was a thoroughly bad egg actually. It’s easy enough to make mistakes in life but on the whole the principle of ‘first do no harm’ is what I see in the lives most folk lead. They, unfortunately, like the innocent victims of Hiroshima and Nagasaki haven’t any control over the bad eggs, military men and the consequences of their megalomania.
        The inference is that we can all dissociate humankind into dots if we categorise them into ‘the other’ through race, class or religion or if there are profits to be made (Lime was a racketeer who caused deaths of children … (dots) … through watered down penicillin), or even simply to protect our own patch (opinions, beliefs etc. – gated communities).

  • Neville says:

    Solar energy is a dangerous, super expensive and unreliable joke. The world’s largest solar plant has recently caught fire and part of the plant is now closed. Another plant is actually roasting birds that are unlucky enough to fly through it at the wrong time. Just an endless waste of billions $ and zero change to temp or co2 levels.

    • BB says:

      Yes Neville I have never understood why Don thinks solar is a possibility. He and I are in Canberra here we get 5 hours a day equivalent. That means you must have energy storage for 19 hours of the day. The amount of energy the Australian Eastern Grid distributes per annum is huge. 200 TW hours. I don’t think there is anything on the horizon that can store that amount of energy. Pumped storage would be the closest but we need units that have capacity measured in the terawatt hours for solar to be ever viable. We also should not forget this is just electrical energy there is a lot of oil used in transport and I think it is just as important if not more so than electrical energy.

      • Don Aitkin says:

        Maybe it’s a dream, BB. But I watched and helped the growth of research into solar energy in the 1980s, and maybe picked up some enthusiasm from what happened then. Solar technologies will continue to improve, I expect, and we will learn from the failures.

        • Neville says:

          Don I’ll just repeat what Lomborg’s team says about Solar energy. Who knows what the future holds, but S&W seem to be a dismal failure so far and no one can explain how this can mitigate their CAGW.

          “The Paris climate treaty will cost around 2 per cent of global GDP and fix much less than a tenth of the problem. Less effective but more ambitious climate policies cost at least 6 per cent of global GDP per year and likely much more. Wind and solar, which covers less than half of one percent of global energy, costs dozens of times more than their climate benefits. Electric cars provide perhaps a thousandth in climate benefit of their substantial public subsidies. Biofuels are just hugely costly while increasing emissions.”

      • Chris Warren says:


        5 hours is not relevant and you provided no reference. The real criteria is the amount of energy and you can see at:

        that Canberra is over 15 – 18 megajoules per square metre per day.

        10 square metres would collect 2.77 KwHr per day.

        • spangled drongo says:

          Try living in the real world, blith, and see how good solar really is.

          A few years ago the Qld govt built a solar thermal [better than PV] station at Windorah which is off-grid.

          It cost the taxpayer about $100,000 per house to build [25 houses, $2.5 million] and the town already had a diesel generator that used around 100,000 litres of fuel per year so they retained the generator as back-up.

          Guess how much diesel fuel they use now?

          Yeah, that’s right, around 100,000 litres per year!

          If, instead of building this white elephant, which also has a huge maintenance cost, the govt had said to each householder, “we’ll give you a one-off $10,000 to provide your own power”, or left things the way they were, how much better off would we all have been?

  • Aert Driessen says:

    Don, you say that there are several estimates/projections of population growth over the rest of this century other than the 12 billion of the RCP8.5 report. I would be interested to know if any of those projections take account of the different birth rates between ‘western’ and Muslim cultures. From what I hear there is a significant difference and that such a difference might lead to other scenarios that might affect real outcomes by 2100 (like civil conflicts). Or does the PC culture forbid such discussion?

    • Don Aitkin says:

      Art, it is hard to find actual official statistics about rates by religion (not ethnicity). But the general evidence seems to suggest that as Muslim immigrants enter Western countries they begin to adopt some oft cultural patterns of the host country, including education. So Muslim girls go to school and can do well. The basic link is that the more education girls have, the fewer babies they have (because they become skilled, gain independence). This does seem to apply to everyone, even if the rate of change is slower for Muslims. There is a world of difference between Malaysia and Saudi Arabia, even though both are Muslim countries.

  • Neville says:

    In this recent UK Telegraph article Lomborg looked at the cost and benefits of our climate change policies. This is how he finished his column.

    “This suggests that a policy which could eradicate global warming for 1 per cent of global GDP would probably be a good deal. Unfortunately, we do not have such a deal on the table. The Paris climate treaty will cost around 2 per cent of global GDP and fix much less than a tenth of the problem. Less effective but more ambitious climate policies cost at least 6 per cent of global GDP per year and likely much more. Wind and solar, which covers less than half of one percent of global energy, costs dozens of times more than their climate benefits. Electric cars provide perhaps a thousandth in climate benefit of their substantial public subsidies. Biofuels are just hugely costly while increasing emissions.

    When we shift the climate conversation to describe positives along with negatives, and focus on costs and benefits of policies – essentially treating this challenge like any other policy agenda – it becomes obvious how many of today’s accepted climate policies are poor. Little wonder climate campaigners do not want this sort of conversation.”

    Here is the full Telegraph article.

  • David says:

    “…and it is really quite rare to find a paper in climate science that is only about observations”

    Well of course it is. Unless you are a savant that can just look at a page of temperature data and make sense of it you will need system (aka a model) and probably a computer to calculate a mean or two to interpret the data.

  • Mike says:

    RCP8.5 is all about a command economy or least one in line withe old “future is certain” maxim. I don’t know if carbon trading can be graced by the term “economic reform”. Maybe trade will stimulated by taxing air. I wish someone would explain how.
    Thank you Don, for these essays

  • Neville says:

    It looks like the UK will be reducing their idiotic carbon tax to try and save 15,000 jobs plus future employment prospects as well. Here is the GWPF article and this quote. Will the OZ electorate wake up and grow a brain before the July election?

    “On the same day hundreds of steelworkers are set to march through London to demand the Government ensures a responsible sale of Tata UK and draws up an industrial strategy. More than 15,000 jobs are at risk if Tata’s UK steel operations cannot be kept open.

    The Government has been criticised for failing to respond soon enough to the crisis caused by cheap Chinese imports and longstanding, high energy costs, with green taxes cited as a key reason for Tata’s decision to sell its UK division.

    The ‘carbon price floor’ introduced by Chancellor George Osborne in 2013 taxes CO2 emissions and makes up more than half the UK power bills for industry. Prices in France and Germany are half those here.

    The tax is £18 per tonne of carbon dioxide and is due to rise to £70 per tonne of CO2 by 2030. British carbon emitters pay the tax on top of levies imposed by the European Union’s carbon emissions trading scheme.

    One potential Tata UK bidder, which said it had been in regular discussions with the Government, said it was ‘increasingly optimistic’ that the Government was prepared to modify the carbon tax regime ‘because of the competitive disadvantage it causes’.”

  • Neville says:

    This Gouretski et al 2012 study shows much higher warming rates in the Arctic before 1950. Just more evidence that backs up the Vinther et al study that shows the same trend. So where is the co2 impact after 1950? Also the Leclercq world glacier study found a slowing of retreat after 1950.

  • Neville says:

    Could our efforts to combat their CAGW be making things worse? Another top post from the Climate etc blog.

  • […] is, not coincidentally, the most favoured pathway if you are an alarmist writer. I wrote about it here. RCP 8.5 is not, as often claimed, a ‘business as usual’ scenario, but a highly […]

  • […] coal use, and low development of technology. It doesn’t have the right smell, at least to me, and I wrote about it in this vein some time […]

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