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, here, here, 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.