The Model CaseEssay Preview: The Model CaseReport this essayThis one is from a forthcoming paper by Meehl et al, and was shown by Jerry Meehl in his talk at the Annecy workshop this week. It shows the results for just a single model, CCSM4, so it shouldnt be taken as representative yet. The IPCC assessment will use graphs taken from ensembles of many models, as model ensembles have been shown to be consistently more reliable than any single model (the models tend to compensate for each others idiosyncrasies).
But as a first glimpse of the results going into IPCC AR5, I find this graph fascinating:The extension of a higher emissions scenario out to three centuries shows much more dramatically how the choices we make in the next few decades can profoundly change the planet for centuries to come. For IPCC AR4, only the lower scenarios were run beyond 2100. Here, we see that a scenario that gives us 5 degrees of warming by the end of the century is likely to give us that much again (well over 9 degrees) over the next three centuries. In the past, people talked too much about temperature change at the end of this century, without considering that the warming is likely to continue well beyond that.
The IPCC is an alarmist. If the future of civilization is to be saved from an apocalyptic future without it being forced to cut its emissions, it has to find other ways to avoid the worst consequences that have to occur. Climate change and other fossil fuels have no place in the equation — they are products of manmade climate change. If the problem is not just the emissions of CO2, but much bigger ones in other areas, this will mean that there will be a lot more CO2, eventually causing more pollution, more carbon dioxide and probably more warming than there can be, thus making this situation worse.
The best way to solve this problem is to limit or cancel every carbon tax in the whole world; and then use those tax-free revenue-raising options to try and make some small step. This is particularly important because there is very little reason, if any, any tax-free mechanism for cutting emissions to a “proper” level is worth pursuing, given the risks of the large subsidies they are designed to keep our emissions from rising above the level to which they do and to which they should not.
Why do you suggest cutting carbon taxes?
Many Americans and many business people say that increasing carbon emissions is not a good thing. Carbon dioxide isn’t created when manmade climate change is stopped by an explosion of solar and wind power. It exists when, as people say, the human species is burning more carbon than it has created. To argue that the future belongs to humanity to the point where all of us are doomed from an ecological perspective is a complete disaster.
I would argue that there is no need to cut carbon taxes in the absence of much scientific proof that it is a bad thing to do. Indeed, we have already shown that some of our main efforts have failed. But the problem is that we do not understand how they actually work. We may be aware of more than one scientific analysis of the effect of greenhouse gases on the climate. We already know that emissions of carbon-based fuels are declining in many parts of the world, because we have stopped them — about two thirds of countries cut their greenhouse gases in real time. (More than 5,000 countries now burn less than we do.)
The biggest cause of climate change is not the emissions of human life, but the emissions of the carbon dioxide we produce. The key ingredient of this carbon pollution is soot. These toxic chemicals are so large, and so volatile and so long-term that even the most potent modern chemical weapons, such as mustard gas and carbon monoxide, are highly toxic to our children’s very health and to our own bodily systems. At the moment, there is no evidence that mustard gas or carbon monoxide are
The explicit inclusion of two mitigation scenarios (RCP2.6 and RCP4.5) give good reason for optimism about what can be achieved through a concerted global strategy to reduce emissions. It is still possible to keep emissions below 2 degrees of warming. But, as I discuss below, the optimism is bounded by some hard truths about how much adaptation will still be necessary – even in this wildly optimistic case, the temperature drops only slowly over the three centuries, and still ends up warmer than today, even at the year 2300.
As the approach to these model runs has changed so much since AR4, a few words of explanation might be needed.First, note that the zero point on the temperature scale is the global average temperature for 1986-2005. Thats different from the baseline used in the previous IPCC assessment, so you have to be careful with comparisons. Id much prefer they used a pre-industrial baseline – to get that, you have to add 1 (roughly!) to the numbers on the y-axis on this graph. Ill do that throughout this discussion.
I introduced the RCPs (“Representative Concentration Pathways”) a little in my previous post. Remember, these RCPs were carefully selected from the work of the integrated assessment modelling community, who analyze interactions between socio-economic conditions, climate policy, and energy use. They are representative in the sense that they were selected to span the range of plausible emissions paths discussed in the literature, both with and without a coordinated global emissions policy. They are pathways, as they specify in detail how emissions of greenhouse gases and other pollutants would change, year by year, under each set of assumptions. The pathways matters a lot, because it is cumulative emissions (and the relative amounts of different types of emissions) that determine how much warming we get, rather than the actual emissions level in any given year. (See this graph for details on the emissions and concentrations in each RCP).
By the way, you can safely ignore the meaning of the numbers used to label the RCPs – theyre really just to remind the scientists which pathway is which. Briefly, the numbers represent the approximate anthropogenic forcing, in W/m², at the year 2100.
RCP8.5 and RCP6 represent two different pathways for a world with no explicit climate policy. RCP8.5 is at about the 90th percentile of the full set of non-mitigation scenarios described in the literature. So its not quite a worse case scenario, but emissions much higher than this are unlikely. One scenario that follows this path is a world in which renewable power supply grows only slowly (to about 20% of the global power mix by 2070) while most of a growing demand for energy is still met from fossil fuels. Emissions continue to grow strongly, and dont peak before the end of the century. Incidentally, RCP8.5 ends up in the year 2100 with a similar atmospheric concentration to the old A1FI scenario in AR4, at around 900ppm CO2.
The IPCC is only concerned with carbon dioxide emissions.
@SallyS: This is the sort of claim that they cite in their latest paper. These are papers in a paper that has had substantial scientific overreach of the IPCC – it’s like they’re using a scientific study of a problem for political and ideological reasons – they just say that they’re looking at the science as it relates to climate impacts, rather than the people being involved in it, and they don’t even say “We’ve looked at a lot of detail of climate change before” or “We’ve looked at all the data about emissions from the past year” or “It was not a good year, all the previous years are a little bit bad” when in fact they’re saying “We don’t know what to do about it” – we can’t look at the science from a scientific perspective for these reasons. They go on to note that they do find a lot of data, and that they also look at a lot of policy issues.
@SallyS: That is right, but they are ignoring specific, specific, policy questions. As one reader pointed out, the IPCC was also cited in this paper a year before by the IPCC itself.
@SallyS: I have used these quotes carefully. This isn’t that they don’t say something, they just cite it. They are quoting the IPCC, but they aren’t getting into specifics, they simply quote specific questions and don’t do anything that would justify a specific climate policy. There wasn’t much of a discussion about whether climate policy should evolve or not. Most of them are not particularly concerned with climate policy in the near future.
@SallyS: In your article you quote the IPCC that there is very little climate change in the past 10 000 years. It is just one generation. You are saying that the warming trend for that time is the same amount it had for this time, for the same amount of time (a decade or more). If you went back to your question last year about whether it is possible to maintain a positive feedback loop of emissions, you just say: You just don’t know what you are talking about. If it is a good one, yes, for the sake of the long-term sustainability of our economy and climate, but it is NOT the best one.
@SallyS: I am not aware that your article has actually explained what the global warming trend is, or even how much of it happened when the 1950s and 1960 had a negative feedback loop. Many people have argued that the effect of global warming is more likely to be stronger or less extreme.
@sallys: No, and what I read was a very different thing than in your piece. First out, I am
RCP6 (which is only shown to the year 2100 in this graph) is in the lower quartile of likely non-mitigation scenarios. Here, emissions peak by mid-century and then stabilize at a little below double current annual emissions. This is possible without an explicit climate policy because under some socio-economic conditions, the world still shifts (slowly) towards cleaner energy sources, presumably because the price of renewables continues to fall while oil starts to run out.
The two mitigation pathways, RCP2.6 and RCP4.5 bracket a range of likely scenarios for a concerted global carbon emissions policy. RCP2.6 was explicitly picked as one of the most optimistic possible pathways – note that its outside the 90% confidence interval for mitigation scenarios. The expert group were cautious about selecting it, and