IPCC report: not smelly enough

“The IPCC’s long-awaited 5th report exploded onto the international scene on 29 September and has monopolised front pages the world over ever since.”

Well actually, no, it didn’t. The impact  of the 5th Assessment Report (known as AR5) was more like that of a loud fart at a party: everyone pretended not to hear it and was immensely relieved when it turned out not to be a smelly one. There was no mention of it, for example, on the home page of Le Monde’s website, nor in any of the main sections – Politics, Economics, Society, Technology. Further down came first Sport and then, finally, Planet. Nuff said…

As was expected, the news is not good. AR5 confirms all the main conclusions of the previous report, which is to say:

  • Global warming has been a reality for decades and will continue for further decades if not centuries.
  • The main cause is the large-scale emission of CO2 linked with human activities over the last 250 years.
  • The ensuing climatic disruption will have a widespread and negative impact on life as we know it.
  • Measures already in place or envisaged will not suffice to ensure that that impact does not become catastrophic.

Furthermore, reading between the lines of the different scenarios, we can discern a clear warning that we have 30 years at most to get it right. If we cannot establish “substantial and sustained” reductions of CO2 emissions within the next two or three decades, it is “likely” (i.e. >66% probability) that the +2° threshold will be broached by the end of the century.

That said, an IPCC report is always something of a parson’s egg. When reading it – or reading about it – there are two things you need to bear in mind:

  • It’s a serious job of work. The contributing scientists know that their report is going to be the standard reference for years to come and they will have done their damnedest to make sure they get it right. In other words, if it’s in an IPCC report, you can be sure it’s “true” – or at least that the methodology is beyond reproach.
  • At the same time, the IPCC works to a remit which virtually ensures that its conclusions will be conservative at the least and perhaps excessively so. For the politicians have the last word and they don’t want to rock the boat any more than they absolutely have to. When dozens of different countries reach an agreement – any agreement – you can be sure that the common denominator they retain will not be the highest. That’s why the final week before publication is called a negotiation. And that in turn leads to a second axiom: if it’s not in the IPCC report, it ain’t necessarily “untrue”.

In the light of these two points, and especially the second, there are three things in AR5 which, it seems to me, need to be looked at very closely :

  • the +2° scenario which has become the standard reference;
  • rising sea level predictions, which are optimistic to say the least;
  • and the inclusion of that final paragraph about geoengineering.

1. The +2° scenario

1.1. The assumption that a 2° increase is acceptable

This scenario, which has come to figure widely in public discourse, envisages a 2° increase in mean temperatures at the surface of the Earth, as compared to preindustrial times, by the year 2100. It also assumes we can live with the consequences of that increase. Now, this latter proposition is a judgement; and I can find no trace of it in AR5. The scientists refer constantly to the likelihood of such and such a hypothesis leading to a 2° increase, but nowhere do they mention relative levels of danger below or above that figure. The idea that “+2° = OK” was just about the only thing the politicians agreed on at the Cancun conference in 2010 and has since acquired quasi-official status. Among politicians, that is; and hence in the minds of those members of the general public who are listening.

Today, temperatures are up by about 0.85° on the pre-industrial reference point. That rise continues and is accelerating. Each of the last three decades has been successively the hottest since 1850 and the 30yr period to 2012 was “likely” the hottest for at least 1,400 years. Since the 1950s changes have been observed which are without precedent over thousands of years (cf. §B and B1 of the Exec. Summary).

Nonetheless it would be a mistake to assume that what we’re seeing today is the total effect of that 0.85° increase. The Earth system is unimaginably vast and complex, and that extra energy is still working its way through. Even AR5 says explicitly that ocean temperatures will continue to rise for several centuries. The phenomena we observe today (extreme weather events, ice-melt, disruption of the water cycle…) must be seen as the beginning of the effect of just 1° of global warming.

Moreover, we forget at our peril that change induces change. Increased atmospheric CO2 causes the permafrost to melt, releasing more CO2; where pack ice has melted the sea absorbs solar energy more readily than the ice did. All in all, there is a real danger that the rate of change could become exponential even before we get into the second degree of temperature rise.

It seems to me that “+2° = OK” is not particularly convincing. Not at all in fact. The only reasonable assumption has to be that any further global warming could and probably will have catastrophic consequences.

1.2. The IPCC numbers

AR5 says it’s possible to limit global warming to 2° by reducing CO2 emissions. The report examines four scenarios, based on lesser or greater rates of reduction. The four scenarios have strange-looking names (RCP2.6, 4.5, 6.0 and 8.5) which no doubt reflect the methodology behind them. I suppose the detailed explanation will figure in the main report due out next year. But that doesn’t do me a lot of good because I also suppose that the maths will be beyond me and I need to get a handle on the IPCC numbers now.

There is a further complication in the fact that politicians and commentators talk in terms of percentage reduction of CO2 emissions, whereas the numbers in AR5 are based on cumulative emissions. This means that, to make a comparison, you have to simulate future emissions and jiggle around with the percentages till the numbers come out looking right. I’m sure there’s a more erudite term for that!

Finally, IPCC numbers express GtC (atmospheric carbon) and not CO2. This explains why my own numbers looked obviously wrong till I divided them by 3.67!

I took as my starting point the 20yr period to 2012, when annual CO2 emissions rose from about 21 to 31.7 GtCO2. That’s an average yearly increase of 2.21%. I then extrapolated from that through to the year 2100, applying different percentages, both positive and negative.

This what came out:

CO2 emissions_modifié-1


Cumul CO2 v2_modifié-1


Fig.2 illustrates the scale of current emissions trends in comparison to what the IPCC says we can get away with. AR5 identifies an emissions threshold beyond which global warming would be likely to exceed +2° irreversibly: 1,000 GtC of total cumulative emissions since pre-industrial times. That’s the global budget, as it were: the red line on the graph. The thing is, we’ve already ‘spent’ 530 GtC, represented on the graph by the dotted white line. Only one of the four AR5 scenarios stays below that line. If the current trend continues we shall exhaust the global budget in about 2148 and we shall have nearly tripled it by the end of the century.

Quite clearly, the required degree of change is incompatible with our present way of life.

We should avoid drawing too much comfort from the AR5 best case scenario, which “only” requires a yearly 3% reduction. For one thing, that’s 3% year after year after year, starting in 2013; and that, childers, ain’t gonna happen. For another, that 1,000 GtC threshold is relevant only to the probability of limiting global warming to +2°; but, as we saw above, there is nothing inherently safe about 2° of global warming.

Concerning Fig.1, there are two points to be made:

  • We are currently heading skywards along the red curve. The further we allow it climb, the steeper will be the cuts required to compensate.
  • I’ve read one commentator saying that the AR5 worst case scenario tracks current trends. Well, not on my figures. And that is not anodyne. AR5 is going to be the reference for years to come and, that being the case, only AR5 numbers will be so to speak “quotable” (otherwise the so-called climate-change sceptics – I think of them as terrorists – will make so much fuss you won’t be able to get a word in edgeways). In other words, anyone trying to talk about real numbers will be accused of ignoring the standard reference, but the standard reference ignores the real numbers necessary to an understanding of the overall picture: Catch 22!

1.3. To sum up

  • The notion that we can live with 2° of global warming (which I venture to suggest is fast becoming a certainty for some) is a political fiction and is not supported by AR5.
  • The AR5 numbers understate the scale of the problem and thus the urgency. In terms of the public debate over “What to do now,” that is regrettable to say the least. Some might even call it a lie of omission.

2. Sea level

Unlike quantum mechanics, climate science ought to leave room for common sense, but unfortunately that’s a luxury the IPCC does not enjoy. They are forced by the mendacious clamour of the OKAY-K mob to leave out anything that is not supported by reams of data and cast iron methodology. On the one hand, this is a strong point, as I mentioned at the top of this article; but it can be a serious obstacle when it comes to getting a handle on the overall picture. Greenland ice melt is a case in point. You really can’t talk about sea level without taking Greenland into account, but AR5 says there’s not yet enough evidence to do so.

What they do say is that the Arctic region is going to warm more quickly than the global average, and not by a couple of peanuts after the decimal point but by as much as 3°. That is considerable.

They also provide what figures they do have (“very likely” means >90% probable):

The average rate of ice loss from the Greenland ice sheet has very likely substantially increased from 34 [–6 to 74] Gt yr–1 over the period 1992-2001 to 215 [157 to 274] Gt yr–1 over the period 2002-2011. {4.4}

These figures represent net ice loss (i.e. new snow fall is taken into account) but they lack precision. The average over a ten year period doesn’t tell us much, but we shall have to wait for the full report and the contents of that §4.4 to get the breakdown. Meanwhile we can safely assume that 2011 ice melt was closer to 300 Gt than to 200. Remember too that 1 Gt of melt represents a cubic kilometre of ice. So 1,810 km3 were added to the sea in the ten years to 2011. That sounds quite dramatic, but the Greenland ice pack contains about 3m km3.

Now, basically, you can look at these numbers in two very different ways.

  • You can say that Greenland is losing 1,810 Gt of ice per decade. In this case, by the end of the century only a fraction of the ice sheet will have melted and sea level will have risen by about 28cm.
  • Or you can say that ice melt is increasing decade on decade by a factor of 215÷34=6.32. In this case, the whole ice sheet will have melted by the middle of the century and therefore sea level will have risen by about 8m. Reducing the rate to a factor of 3 only gains 15-20 years.

AR5 appears to have opted for the former, more comforting, hypothesis. In the sense that, clearly, you cannot reasonably extrapolate from just two numbers, they are entitled to do so.

The basis for higher projections of global mean sea level rise in the 21st century has been considered and it has been concluded that there is currently insufficient evidence to evaluate the probability of specific levels above the assessed likely range. Many semi-empirical model projections of global mean sea level rise are higher than process-based model projections (up to about twice as large), but there is no consensus in the scientific community about their reliability and there is thus low confidence in their projections. {13.5}

Translation: we can’t agree among ourselves so we’re hiding behind the “insufficient evidence” line. Fair enough, in the circumstances.

But this is much more emphatic:

Based on current understanding, only the collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century.

And this is misleading:

There is high confidence that sustained warming greater than some threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or more…

In fact a flat-rate loss of (rounding up) 2,000 Gt per decade leads to complete melting of the Greenland ice sheet in 15,000 years. But this scenario is obviously so improbable that even to mention it is frankly disingenuous to say the least. It’s one thing to keep quiet about stuff you don’t have enough evidence for, but another to be falsely reassuring. Splitting hairs? Not at all: this kind of thing will be seized upon by the politicians to justify further delay and by the climate-change terrorists to scoff.

Given the colossal importance of what “future understanding” could reveal, is it reasonable to dismiss the worst case scenario out of hand? Common sense would say no, if only because the IPCC runs the risk of looking extremely silly if (or rather when) the next major study confirms exponential ice loss; and for the IPCC to suffer such a loss of face would not be good for science.

3. Geoengineering

During the week before publication of the AR5 Executive Summary, when the scientists – or rather their political masters – were negotiating final terms in Stockholm, reports appeared in the press saying that the Russians were trying to include a paragraph on geoengineering. They were roundly condemned by the commentators, and rightly so: you can’t just tack on an extra bit at the end of a report like AR5, at the last minute, especially when it concerns an area that the authors have seen fit to omit. But to general surprise the Russians won through: why be reasonable when hard-headed and thick-skinned will do the job?

The effect of this Russian “success story” is far from insignificant: it means that the geoengineering card is now officially on the table. By definition, AR5 fixes the framework of public debate for the next several years, so geoengineering has now been admitted to that debate. And that is definitely not A Good Thing. In fact it’s A Very Bad Thing.

(I take it as read here that geoengineering is a non-starter or at best a last resort gamble, for the simple, obvious reason that it cannot be experimented: it gives you one chance and only one to get everything right, failing which the chances of doing severe, irreversible damage to the biosphere are astronomical.)

Nonetheless, the Russians insisted and it’s not hard to see why. The Russian economy is largely dependent on exports of cereals and fossil energy. Severe and repeated droughts have already hit cereal exports; anything that threatens the value of energy exports could bring the whole house of cards tumbling down.

Worse, that could come about by anticipation when the carbon bubble bursts. Identified reserves of oil and gas count as assets on the national balance sheet and are valued at millions of millions of dollars. The day the international community gets its act together and declares that those reserves have to stay in the ground, those assets have to be written off and Russia’s balance sheet falls apart. The effect will be immediate: think of a virus-stricken spread sheet reduced to a jumble of numbers at the bottom of the screen.

With geoengineering now officially on the agenda, Russia is free to pursue business as usual while counting on a quick fix to solve the underlying problem – some time in the not too near future. That suits everyone: the oil industry carries on making huge profits, and the politicians wriggle out of some (admittedly) impossibly difficult decisions.

To differing degrees, other countries face the same predicament. The Stockholm negotiations must have been very interesting. Who paid what, I wonder ? For there’s little doubt in my mind that Russia must have got something out of being the one to say out loud what the others were thinking.


For the informed and well-intentioned reader of AR5, the writing is on the wall. But this report will have failed to deliver the salutary shock which is so desperately needed to shift public opinion and thus the politicians. Too much is left unsaid between the lines. The politicians will continue to defy logic and the evidence, while the curves on the graphs get inexorably steeper.

(This post was modified on 30 October 2013 to include a more coherent version of Fig.2.)

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