[A short version was published by the Canberra Times, 2 Feb, as “Evidence Points to Catastrophic Climate Change”. A longer version was posted on On Line Opinion, 8 Feb.]
In a new scientific paper (pdf, 600kb) prominent climate scientist James Hansen and his colleague Makiko Sato argue that the Earth is now at least as warm as it was between earlier ice ages, and further warming by even one degree celsius could result in sea level rising by anything from 5 to 25 meters, with perhaps 5 meters rise by the end of this century.
This implies more stringent limits than current, politically-adopted targets to keep warming below two degrees celsius and atmospheric carbon dioxide content below 450 parts per million (ppm). Hansen now says the present targets are prescriptions for disaster, and that we must keep warming to less than one degree. This requires reducing atmospheric carbon dioxide to less than 350 ppm, from its present value near 390 ppm, as quickly as possible.
Meeting the new targets would require very rapid reductions in emissions of carbon dioxide and other greenhouse gases, and active efforts to withdraw carbon dioxide from the atmosphere. Bio-sequestration (using plants to build carbon in soil) is an option that can be undertaken immediately.
Given that existing policies in most countries fall well short of meeting even the old targets, this adds a new level of urgency to the existing urgency to begin major and effective efforts immediately.
There are three main approaches used to understand global warming: direct measurements of the world at present, computer models, and records of past climate extracted from sedimentary rocks and polar ice cores. The latter, deciphering natural records, has the advantage of looking at natural experiments that include all the complications of the real climate system, whereas computer models do not handle well some difficult factors such as cloud and aerosol variations. It depends, of course, on correctly and accurately deciphering the subtle chemical and isotopic records in the rocks and ice, but scientists have been unravelling those signals for quite a long time and a lot is known. Hansen and Sato have built on earlier work using recent data sets.
Over the past million years or so the climate has swung between ice ages and briefer, warmer interglacial periods. For the past 10,000 years, during which civilisation developed, we have been in a warm period called the Holocene in which temperature and sea level have been unusually stable. (Graph courtesy of ClimateCodeRed blog.)
Global temperature before, during and after the Holocene Epoch
The old targets, limiting the temperature increase to less than 2 degrees celsius and carbon dioxide to less than 450 ppm, were based on ice core records, which indicated that two previous interglacial periods, about 120,000 and 400,000 years ago, were 2.7-3.7 degrees celsius warmer than the Holocene (see graph (a) below). At those times sea level was 5 metres or more higher than now.
Ice age temperatures. The blue reference curve in both plots is calculated from known ice extents and greenhouse gas concentrations. The upper panel (red) shows and ice core record. The lower panel (red) shows the deep ocean sediment record.
However Hansen and Sato now argue that the ice core record is affected by extra regional warming over the polar ice sheets, and it is not representative of the globe as a whole. They argue the deep sea sediment record is more globally representative, and this shows the earlier temperature peaks to have been no more than 1 degree warmer than now.
To explain the difference between the ice core and deep ocean records, Hansen and Sato argue that there are several positive feedbacks that come into play at temperatures near the present temperature, and they would accentuate the warming of polar regions more strongly than the rest of the globe. As temperatures rise through the present level, sea ice melts and ice shelves disappear, so the exposed water absorbs more solar heat than the ice it replaces. Also as surface melting occurs on ice sheets they darken significantly, so they also absorb more solar heat.
At present polar temperatures increase about twice as much as the global average, but the feedbacks would increase this ratio. Thus the ice sheets in the past warm intervals would have experienced the stronger warming recorded in the ice cores. Correspondingly they would have melted more, raising sea level several metres above present levels.
The concerning implication is that further warming by 1 degree or less over coming decades could trigger a rise in sea level of 5 metres or more, similar to levels during the earlier interglacial periods. This is much more than the 18-60 cm rise projected in 2007 by the Inter-Governmental Panel on Climate Change (IPCC) using earlier data, and puts us on the brink of dangerous warming right now.
The urgency of Hansen and Sato’s message is bolstered by records from 3-5 million years ago (during the Pliocene epoch, graph below) which show temperatures no more than one degree warmer than now but sea levels as much as 25 metres higher than now, a rise that would be catastrophic.
Global temperature from deep sea sediments over the past 5 million years.
Hansen and Sato also argue that ice sheet melting and breakup is an exponentially accelerating process that doubles its speed every 6-10 years, rather than a steady process. This implies that sea level rise would be much faster than previously thought. An accelerating process is expected because melt water tends to lubricate the bases of glaciers, which flow and break up more quickly, and because substantial parts of the West Antarctic ice sheet are grounded below sea level, so ocean warming and ice thinning can float their edges away more readily.
Melt rates, ice mass losses and sea level rise have all been measured to be increasing, consistent with these arguments. However the data do not yet extend for a long enough period to confirm that an exponential doubling process is occurring, and to accurately estimate the doubling time. The data are consistent with a doubling time of 6-10 years, and this will become more accurately known over the next 5-10 years. Even a doubling time of 10 years allows nine doublings this century, so rates could increase 500 times, to metres per decade by 2100.
Hansen first advanced arguments along these lines in 2007, but the new paper brings more data and insights to bear, and moves the conclusions from conjectural to plausible. There are of course many who deny that global warming is caused by human activity. Most such claims are based on only small portions of the wide range of arguments mentioned earlier. The Hansen and Sato conclusions do not require computer models of climate, and they are quite independent of the climategate controversy, which in any case was an enormous beatup of some private discussion of quite peripheral data sets. It is past time that policy makers gave serious attention to those whose long and successful careers, under the scrutiny of rivals, attest to the breadth and depth of their understanding.
A sea level rise of several metres would devastate global civilisation, as large populations, many cities and much infrastructure are within only a few metres of sea level. After the extreme weather of Black Saturday, February 7 2009, Australia added the “Catastrophic” category of bush fire danger above the previous highest “Extreme” category.
The danger from global warming may have moved from extreme to catastrophic.
The new Australian fire danger scale, introduced after the catastrophic fires of Black Saturday, February 7 2009.
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Hansen says a lot of things. Here you are talking about everything he says as if it were revealed truth and carelessly passing Hansen’s nonsense on. Pull yourself together and start exercising some independent judgement.
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Graeme, I have 40 years’ experience doing peer-reviewed science, which means I am well practised at critiquing my own work, and then being critiqued by others before I get to publish. I am also well practised at critiquing others’ work, and apply that experience when I read stuff by Hansen or anyone else. So I am impressed by the quality of his arguments and don’t treat them as revealed truth. I also know the limitations of his arguments.
I commend to you the process of formally writing your ideas up and submitting them to others for critical comment. That is most easily done by submitting them to a scientific journal.
In the mean time, don’t, on this blog, write as though you are the only one in the universe with independent judgement. And don’t just fling the accusation about a grand conspiracy to shut out contrary views. It is the last retreat of those bereft of decent arguments.
Also see my other response to you on the “Hansen misrepresented” thread.
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How can you possibly be impressed with his arguments? They make no sense at all. They are made on a god-of-gaps basis. You might well have pleased insular priesthood reviewers for 30 years, but now you face something more difficult. You face a conceptual audit from outside of any narrow specialty. Believe me I won’t fail in my logic.
So fire away. Make your case. You haven’t done very well so far. A simple appeal to authority, including you own, isn’t going anywhere with a conceptual audit.
Current peer review, even when its working well, ensures little more than accurate data gathering. You face something a little bit trickier here. The first step is context. Then I would ask you to think of an upside-down pyramid. All assumptions have to be built from the ground up. the lower on the pyramid, the more important it is not to get it wrong, since one does not wish to build on mistakes.
What can one say about the context of the overall argument?
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Graeme, here I am not writing scientific papers with the full case laid out. I am summarising scientific work that has been or will be submitted to critical review. That review is generally a thorough look at assumptions and logic as well as data. Your characterisation of a narrow priesthood checking data is just the grand conspiracy theory in different dress. You are not telling me anything new about how science should be done. How much experience do you have?
So far, your critique of Hansen is that his arguments “make no sense at all”, not exactly searingly insightful.
I don’t propose to debate the science at length with you. I don’t think you’re persuadable, and the science is out there if you had a serious interest.
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There is no “you said conspiracy” trump card in logic. I take an Augustinian view of human institutions and most of them tend to dysfunction. I studied all aspects of this controversy from 2005 to 2009. You seem to be a latecomer. I assure you this is all fraud and poor logic. There is rife data-rigging. If you don’t believe me, then you better check the data quality out for yourself.
The starting context of this matter is that we are in an ice age. The global heat maximum was 55 million years ago. According to conventional accounts our ice age started at 39 million years ago, though this is quoted variously. And we have been in a particularly brutal phase of this ice age for about 3 million years. During most of the last 3 million years we have been on a planet that is fundamentally too cold for diverse landed animal life, although sea life flourishes during the cold times.
The glacial periods are long, the interglacials short. The glacial periods are the norm. The interglacials are the exception.
The 55 million years have been one long cooling cycle viewed at the millions of years level. Nothing indicates that this will change, except that ice obstruction (to the great ocean conveyor) appears to be a strong factor so we can do something about that.
The CO2 does not appear to be any sort of amplification factor. Correlation is not causation as you know. And the CO2 follows and does not lead the temperature trends. Although we are really only going on the ice core data, and evidence is not good evidence unless it is convergent.
Conventional science focuses on minute arguments within dominant paradigms and shies away from debates between paradigms but the scientific pursuit ought to be between the wider arguments rather than a playing out of some specialists curse of the small stuff.
I say that the amplification is due to the viscosity of water and to ice obstruction. You say its due to CO2. Its BETWEEN conflicting large arguments where the most effort ought to be expended.
Your model is based around watts, gases, and black bodies and it hijacks surface temperature of a black body and substitutes for air temperature. I focus on joules and strata.
If our energy intake were as stable as we pretend it to be then the equilibrium temperature of earth ought to be most determined by air pressure, and secondly by ease-of-resistance to circulation. There is plenty of evidence that this is true and it follows directly from the Stefan-Boltzmann law that this ought to be true. Hence the connection of the development of the Isthmus of Panama, cutting off Atlantic from Pacific …. to our most recent nasty phase of our longer ice age.
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Graeme –
By all means keep an eye on the big questions, but when you make such generalisations as you’ve just done there’s little to comment on, because it’s so vague and unspecified.
You make general denunciations of virtually all scientists and their data, so you can say anything you like after that and no-one can argue with you.
Except – I didn’t imply correlation is causation. Causation is established elsewhere, and then correlation yields the magnitude of the relationship. The reason temperature leads CO2 in the ice ages is then explanable consistently as amplification. If you can’t follow what I’ve said then again there’s no point in trying to debate.
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“Except – I didn’t imply correlation is causation. Causation is established elsewhere….”
A big call. This is what I’d like to see. I’m not having difficulty following you. The problem is that causation is not established anywhere.
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Graeme, I’m not sure what would persuade you. Science is never about proof, it’s about plausible stories that fit the known observations. In this sense the physics of CO2 absorption is well established. Given that, Hansen’s ice age story makes sense.
As you dismiss mainstream scientists and their data out of hand, I’m not sure there’s a profitable debate here.
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“Graeme, I’m not sure what would persuade you. Science is never about proof…”
Science is definitely about proof. Science is always about proof. Or do you still defer to Galen, and not realise that the heart is a pump? Do you follow Ptolemy, and say that its an open question whether the earth orbits the sun, or that it could be the other way around?
Science is in fact the search for proof. And proof is found through convergent evidence in the context of developing competing paradigms in parallel. You cannot persuade me since you are wrong. You have come in on the wrong side of this argument. You are doing rather better on the economics side because you are looking at matters through fresh eyes and are hammering the neoclassical consensus.
You are perfectly capable of finding out, as I have found out, that the data is rigged. I assure that this is the case. Its not rigged in subtle and hard to identify ways. So if you choose not to do, what for you would be very little work, and confirm this matter, well thats falling down on your calling.
The physics of absorption is well established. This is really about the colour of CO2. Its just a gas colour. The question was whether what was found in the lab, translate to certain predictions made for the troposphere, or have those predictions turned out to be wrong? You cannot reinsert in the conclusion to the inference, that which was used to make the inference in the first place.
The extrapolation of the colour of CO2, having these large effects on temperatures was a single inductive inference. You ought to know that such pieces of armchair thinking are the bread and butter of creativity in science. A good scientist ought to make three or four such inductive inferences before breakfast. A good scientist will also know that most of these examples of armchair thinking will turn out to be wrong, just as this one has.
Now on the other hand, if you take my paradigm, and start looking at resistance to circulation, right on this very page on your very first diagram you will have evidence to see that I am on the right track, and need no rigged data to reinforce my inductive inference, an inference made straight from the Stefan Boltzmann law.
Look to the younger Dryas. See the reversal of a warming trend which is held to have happened as a result of Lake Agassiz bursting and cold fresh water landing directly down onto the gulf stream. There we have a 1000 year reversal of the warming trend, until the Gulf Stream started up again, and not merely a redistribution of the available heat. To spread the joules out is to more successfully retain them.
And this is a very important matter and not to be crowded out by bad science. People have began to use the Gulf Stream for energy generation. This is a worrying trend though the proponents will cause this trend “green”. Buying land for nature corridors is green. Impeding the Gulf Stream is courting disaster.
Warming and cooling get locked in because colder water is more viscous, and because you get all this ice impeding matters off Hudson Bay. You will see this showing up in the record very clearly if you go looking for it.
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Newton proposed a description of gravity that works very well for many situations. Einstein proposed a very different description. It gives very similar results in familiar situations, but differs if gravity is very strong or at the scale of the universe, for example. So Einstein’s description is a more general and therefore more useful one.
The criterion I have just used to evaluate the two theories was “usefulness”. It was not “truth” or “proof”. If Einstein’s theory works better, does that make Newton’s wrong? I don’t think it’s useful to evaluate them that way. Einstein’s works well, but does that mean another theory may not work even better? So it’s not useful to say Einstein’s theory is “proven” or “truth” or “the mind of god” or whatever some silly people go on about.
That does not mean there is no way to distinguish between Ptolemy and Copernicus/Kepler/Newton. The latter does better, more concisely. And more generally because it describes falling apples as well as orbiting planets.
So we are not expecting to “prove” CO2 causes global warming, but we are expecting to decide whether it gives a broadly accurate description of what is happening, or not.
Regarding Hansen and global warming you say “You cannot persuade me since you are wrong. ” That means in turn you cannot persuade me because you just make bald assertions. End of “debate”.
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Newton didn’t know what caused gravity. He just came up with some formulas to describe it. Whereas the Einstein theory of gravity is merely ridiculous. Gravity remains a mystery to mainstream science. So thats not a good example of how things ought to work, since the scientists are lying down on the job, and have not completed it.
But many things have been completed, and the heart being a pump, the discovery of many moons of Jupiter …. there are endless examples of science proving matters. Its true that they haven’t proved what causes gravity. But this is just an example of 20th century hopelessness.
Where gravity is concerned the scientists have been worse than hopeless. They have been actively obstructionist. They have also substituted the cult of personality for proper epistemology.
Since we don’t know what gravity is, and since scientists will actively obstruct the search for an answer to the mystery of gravity, its not a valid example for how science ought to work.
But there are endless examples of science working properly and finding correct answers without the cult of personality and without obstructionism.
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If you were right about the CO2 you could easily persuade me. Simple as that. There would be no need for rigged data, like with your first graph. The conclusion would flow naturally from the evidence. You wouldn’t have to be in denial about the CO2 being rigged. Matter of fact I thought that CO2 had a warming effect before I knew the data was rigged. But now that I know the data is rigged my justification for thinking CO2 had a warming effect has gone away.
One fellow said that 0.4 % increase per year CO2 leads to a 0.13 degrees Celsius overlay to temperature per decade, and looking at the data, and comparing the temperature to the solar data that looked pretty right. But I had to change that view of matters once I knew the data was rigged and that the 30’s was the warmest decade.
There is absolutely no use pretending that the data isn’t rigged. Because we already know it is rigged. Its not acceptable to base conclusions on rigged data.
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