Some time ago Anthony Watts opened his website to what purported to be a ‘great debate’ on climate science, between William Happer, emeritus professor of physics at Princeton and very recently an adviser to President Trump (Professor Happer and I have corresponded from time to time), and David Karoly, a professor at Melbourne University who has been involved in a number of IPCC reports. I had a particular interest in this debate, because I had debated Professor Karoly myself, some years ago. Apart from saying that there was a lot in what I said that he would agree with, Professor Karoly ignored the substance of my criticisms of the orthodox AGW position and put forward his own views. As opening speakers he and I were not allowed rights of reply, so I remained frustrated throughout the evening.
I was not especially surprised to discover that, having started in the debate, Professor Karoly then withdrew from it in the middle; he was replaced as the spokesman for the orthodoxy, by Glenn Tamblyn, who writes for skepticalscience.com. He certainly comes from the appropriate background! In any case, the debate is full of links and well worth reading, and there is an easy entry to it, another piece on WUWT written by Andy May, in which he does his best to summarise the issues by, as it were, asking retrospectively six questions of the two participants:
- Is recent global warming unusual?
- How do we know the excess CO2, and other greenhouse gases, are from human activities?
- How do we know that the increase in CO2and other greenhouse gases in the atmosphere have caused most of the recent global warming?
- Climate models have been used to compute the amount of warming caused by human activities, how accurate are they?
- How do we know global warming and more CO2will have substantial adverse impacts on humans and the planet?
- Should anything be done to combat global warming?
The debate, or at least Andy May’s arrangement of it, is continuing. The questions are old ones, but at least they are central. What I am writing about here are the retrieved views of both scientists about the six questions.
Question 1 Is recent global warming unusual?
Both Karoly and Mann agree that climate changes, that the world has become warmer over the past 150 years, that adding CO2 to the atmosphere will increase warming, and that warming is continuing at approximately 2ppm per year. Where do they disagree? Karoly asserts that there has been no comparable warming in the last thousand years, and his evidence is largely that of the Mann hockey-stick. Happer points out that the Mann hockey-stick has been eviscerated by experts on technical grounds, and that the IPCC itself dropped it from later Assessment Reports (the diagram figured prominently in the Third AR).
At once we have a problem, because if you accept the Mann hockey-stick at all it is hard to know what to say in response to such acceptance, other than to ask how the speaker deals with the Wegman, McIntyre and other analyses of the Mann methodology, which were destructive in the extreme. What is perhaps more awkward still is that we will never know what the ‘real’ temperatures were between 1000 AD and the beginning of widespread thermometer use in the late 19th century. The proxies that have been used, in what seems to me a desperate attempt to find a human influence signal, just aren’t accurate (fine) enough. We just don’t know, and we probably will never know; and that is really irritating. May provides lots of evidence, and comes to the conclusion that while we know something about the Northern Hemisphere, we know next to nothing about the Southern, and cannot therefore either say that the world was warmer during the Mediaeval Warm Period or that it wasn’t. And of course a great deal hangs on this issue. Is recent global warming unusual? On the evidence it is really hard to come down strongly one way or the other. My own tentative view is that it isn’t unusual, but I would welcome offered argument and evidence the other way, especially that dealing with the climate sensitivity question.
Question 2: How do we know that excess CO2 and other greenhouse gases are the result of human activity?
Karoly provides an argument, based on the ratio of carbon isotopes, that there has been no level of CO2 in the last 800,000 years that is greater than 300 ppm, until you get to the 20thcentury. Happer accepts that the observed increase is indeed the work of human beings. I would like to say ‘largely the work’, but with uncertainty.
Question 3: How much of the global warming has been due to human activity?
David Karoly’s central position is that ‘an overwhelming consensus of climate scientists agree that it[is]’, that it will continue, and that bad things will happen as a result. His subsidiary point is that climate models show it must be so. I have no truck with ‘the consensus’ as a source of authority. We were taught that as undergraduates. They are there to be overturned in time — or confirmed over time through the lack of effective criticism (Popper’s use of falsification). The trouble is that the supposed consensus has not been confirmed over the last thirty years, as I pointed out above. It remains an assertion. It’s not even correct, anyway. There is no consensus about how much human beings have contributed to recent global warming, for climate scientist have never been asked that direct question, and his quoted passage above is not one that contains any number.
Nor can we place much faith in what climate models tell us. They haven’t got things right even when they have the data they need. As has been argued again and again, they start with the assumption that CO2 is the main cause, and Lo! they find that it must be. Happer relies on the evidence that, setting aside the last million years, the rest of the earth’s history shows CO2 at much higher levels than at present, which is one of carbon dioxide starvation. Ergo, high CO2 has natural causes. My summary is that no one knows, and all we can say is that human activity has added to the recent warmth — by how much we don’t know. There are as many estimates as there are estimators.
Question 4: How accurate are climate models?
The canary in the coal-mine for many sceptics is that computer models don’t capture the similar warmings from 1910 to 1945 and from 1975 to 1998, let alone the lack of warming from 2000 to 2012, when CO2 simply kept rising but temperature didn’t. For Karoly these inadequacies are acceptable, for Happer they are not. He explains why (and I agree with his reasons), and he sticks to what he calls ‘real’ measurements — satellite images, ocean pH, real records of extreme weather, and so on. As regular readers will know, that is my position too. Climate models provide useful information, but they don’t provide real data. You have to measure real events and processes to obtain them.
Question 5: Why will increasing CO2 have an adverse effect on humans and the planet?
This is a question that has fascinated me from the beginning of my interest in the issue, for all the obvious reasons. Warm is outstandingly better than cold, for nearly all living things, nearly all the time. Karoly says the adverse effects are already happening, and will continue. His evidence is disputed by many others who look hard at real data, like Pielke Jnr. I don’t think there is any evidence that there have been adverse effects, and I’d be surprise to hear that there are, with real data to back them up. All the evidence os that there warming so far has been beneficial. Karoly sees the oceans becoming more acidic, to the decline of marine species and much else. He does accept that ‘moderate levels of global warming’ may have some benefits, but he plainly thinks that we will rocket past moderate levels, and then everything will be dire. Happer thinks that this level of alarm is exaggerated because, to repeat, the planet is and has been for a long time in a ‘CO2 famine’. More, there was never any tipping point or runaway episode in the earth’s history when high levels of CO2 led to some catastrophe — at least there is no evidence of such an event. And the ocean acidification debate continues, neither side happy with the science of the other. The oceans are vast, and we know far too little about what happens within them and across them.
Question 6: What should we do, if anything to combat global warming?
It is easy to spot the differences here. Karoly says that we have to stabilise greenhouse gases in the atmosphere. His case rests on a climate sensitivity (ECS) producing three degrees C of global temperature for each doubling of CO2. So there is nothing new here, because that is his general explanation for the catastrophe awaiting us with global warming. Happer sees ECS at about one degree, which is what you would expect from the physics if there were no such thing as climate sensitivity. Indeed, to make the point again, without ‘climate sensitivity’ there would no AGW issue at all. The trouble is, no one has been able to locate and measure this fabulous creature.
Happer goes further, and provides a graph to show that it will take around two hundred years to reach a doubling of current CO2 levels. It is not clear to me that we in 2018 have any kind of responsibility to shield our eighth-and-later generation descendants from supposed harm from global warming perceived two hundred years ago. More than fifty explanations have been proposed to explain why model runs offer such poor performance. The most sensible one I rehearsed earlier. They run too hot because they accept ‘climate sensitivity’ at a high level. If you run them without CS, as the Russian model does (and it fits well the real-world data) the case for catastrophe and for government interventions, both nationally and internationally, simply falls away altogether. That is Happer’s position. It is mine too, and after ten years of study of this issue I see no reason to change it.
There is a lot of material in this ‘debate’, though I wouldn’t call it a ‘great debate’ since the outcome required someone else to orchestrate the discussion, but I recommend it to those readers for whom this whole subject remains of continuing interest.