Scepticism about global warming continues, along with outright denial that it is caused by humans, or even that it is happening at all.  Informed debate is healthy, but much of the discussion is ill-informed, much of it addresses the wrong questions, and much of it misconceives science as a source of “proof” or “truth”.

Evidence

The frequent claim that there is no evidence for global warming is silly, though perhaps also mis-stated.  There are vast amounts of evidence, and thousands of scientists are involved in gathering and interpreting it all the time.  The vast majority of them consider that it shows global warming is happening and we are the cause.

Perhaps people who say this mean there is no convincing evidence.  Presumably they didn’t go through all the evidence themselves.  Presumably they are taking somebody’s word for it, someone who claims to be well-informed, but usually they don’t say who their authority is.  If it’s the likes of Ian Plimer, author of Heaven and Earth, then they are sadly misled.  Plimer’s book is a pseudo-scientific hodge-podge, having the appearance of scholarship but indiscriminately quoting so-called evidence most of which has long-since been challenged and found wanting.  For a review of his book see Michael Ashley’s review in The Australian.

A prominent example of someone claiming the evidence is not convincing was Don Aitken, in speeches and papers in 2008.  The sources used by Aitken were traced by Clive Hamilton to a very limited number of people who repeat long-discredited arguments and supposed evidence.  Aitken had not even consulted prominent Australian climate scientists, with whom he must be familiar as a former head of the Australian Research Council.

A common recent claim is that the globe has been cooling since 1998.  This is a misreading or misrepresentation of the evidence, as my recent post shows.

Proof or professional judgement?  Whose judgement?

A critical aspect of the global warming problem is that the full effect of CO2 emissions is delayed by a couple of decades.  This means that by the time we start to see strong effects it will almost certainly be too late, because another two-decades’ worth of (steadily increasing) emissions will have been added that will push the temperature even higher.  We have known all along that our response would have to be decided before the effects were strong and the causation clearer.  In other words we have known all along we would need to act with incomplete knowledge.

How do you proceed when your knowledge is incomplete?  The only way to proceed is to use best judgement.  Whose judgement?  Well, those who know the evidence best – the climate scientists.  You want the collective best judgement of climate scientists.  That is what the IPCC (Inter-governmental Panel on Climate Change) delivers.

The IPCC process

Those who claim scientists, through the IPCC, are simply feathering their nests, totally misrepresent the IPCC and its processes.  The IPCC is not just a gathering of climate scientists, it is an inter-governmental panel.  Members are appointed by governments.  Governments have the final say on what goes into their reports.  Furthermore the IPCC asks hundreds of scientists “What, in spite of the uncertainties and continuing debates, are the things most of us can agree on?”

Thus the IPCC produces a scientifically-conservative near-consensus.  That conservative judgment is then vetted by governments and typically watered down even further.  The 4th IPCC report in 2007 is now widely regarded as too conservative, already outdated when it was published, and  quickly outstripped by new and disturbing symptoms of warming, such as the rapid shrinkage of Arctic sea ice.

Questions

The relevant questions are thus

In the collective professional judgement of climate scientists, is global warming happening?

In the collective professional judgement of climate scientists, are human emissions of greenhouse-inducing gases a major cause of global warming?

In the collective professional judgement of relevant scientists, what are the likely consequences of global warming?

The answers are yes, yes (at least 90% confidence in the 2007 report), and catastrophic.

Scientific proof?

Those who argue that human-caused global warming is not “proven” misunderstand the nature of science.  Despite the widespread stereotype of scientists seeking “truth” or “reading the mind of God”, science is not about truth or proof.  Science is about finding stories that provide useful guidance on how the world works.  Stories that are still tentative are called hypotheses.  Stories that have provided useful and usefully accurate guidance are called theories.

A new theory might be found to be more accurate or more general than an old theory.  Thus Einstein’s theory of general relativity is more accurate and more general than Newton’s theory of gravity.  This does not mean Newton’s theory is “wrong”, “disproven” or “falsified”.  It means Einstein’s theory is more useful.

Thus human causation of global warming can never be proven in the strict logical sense.  In more practical terms, the phenomena are so complicated that there will always be room for debate about details, and there will always be a few who are unconvinced.  The status of a theory depends on the judgements of practising scientists, not on “proof”.

Not just another opinion

Many politicians, jounalists and sceptics treat scientific conclusions as just one more opinion, having no more weight than a lobbyist’s, columnist’s or blogger’s.

This attitude ignores two things about scientific conclusions.  The first is that they are based on evidence and careful testing of ideas against observations of the real world.  The second is that any paper published in a refereed scientific journal has had to run the gauntlet of an editor and up to three critical referees, and once it is published it is fair game for any other scientist to shoot it down if she thinks it is wrong.  Scientific consensus is a product of a critical debate.  No other profession has such rigorous process.  No other claims have as strong a claim to reasonable veracity.

Some of these issues were covered in my article last year for On Line Opinion, which is reproduced below.

Why Listen to Scientists?

By Geoff Davies,  On Line Opinion, 
Posted Monday, 26 May 2008.

Professor Don Aitkin’s recent promotion (PDF 258KB) of the “sceptical” view of global warming and the ensuing heated debates on several web sites bring to the fore the question of what authority attaches to the published conclusions and judgments of climate scientists.

Professor Aitkin, who is not a scientist, is in no doubt himself that the more outspoken climate scientists have a “quasi-religious” attitude. That is the mild end of the spectrum of opinions of sceptics/denialists/contrarians.

Most of the media and many politicians seem to have the view that scientists are just another interest group, and that scientists’ opinions are just opinions, to be heard or discarded like any others. The Australian government seems to credit only the very conservative end of climate scientists’ warnings, because it is acting as though we have many decades in which to adjust, and many years before anything serious needs to be under way.

The big difference between scientists’ professional conclusions and those of others is that science has a pervasive and well-developed quality-control process. The first stage is called peer review. Any paper that is published in a reputable scientific journal must be given the OK by several other scientists in the same field.

Furthermore, after publication a paper will be read critically by many more scientists, and it is not uncommon for conclusions to be challenged in subsequent publications. For a paper to become widely acknowledged it must survive such scrutiny for a reasonable period, typically several years.

All of this is on top of the fact that a scientific paper is based on observations of the world and on a large accumulation of well-tested regularities, such as the “laws” of physics.

Few other groups have any comparable process. Certainly the media, politicians and climate sceptics have no such process. Most of the studies referred to by sceptics have either not been published in a relevant peer-reviewed scientific journal or have subsequently been challenged and found wanting in other peer-reviewed studies.

The peer-review process is far from perfect, but it yields a product distinctly less unreliable than all the other opinions flying around.

The process of the Intergovernmental Panel on Climate Change (IPCC) adds another layer of caution. Basically the IPCC gets a large number of relevant scientists to step back from the front-line disputes and ask “What can most of us agree on?”. Sceptics who dismiss all of the science because there are many disputes miss or obfuscate this basic aspect of IPCC assessments.

There is a degree of judgment involved in the IPCC process, and in virtually any public summary by a climate scientist. Some would claim judgment is not the job of scientists; it is the job of politicians and others. But scientists are the best placed to judge the state of knowledge in their field. If their conclusions are potentially of great import, then they have a responsibility to state their best professional judgment.

The claim by Professor Aitkin and many other sceptics that climate scientists don’t discuss the uncertainties in their conclusions and judgments simply misrepresents or misperceives the abundant information on uncertainties. Even the IPCC’s most terse summary statements clearly acknowledge uncertainty when they say, for example, “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” [emphasis in original]. The term “very likely” is specifically defined in the IPCC summaries to mean the “assessed likelihood, using expert judgment”, is greater than 90 per cent.

Clive Hamilton contrasts the scientific and IPCC processes with those of many sceptics (see Atkin’s response here). He traces connections from relatively naïve people like Professor Aitkin back to people and web sites funded by ExxonMobil and others. Sceptics love to question the motives of climate scientists, but rarely mention the motives of the very powerful multi-trillion-dollar fossil fuel industry, parts of which are actively promoting doubt and disinformation in exactly the manner used by the tobacco industry for many years.

Observations from the past two or three years, too recent to have been included in the 2007 IPCC Reports, show disturbing signs that the Earth’s response to our activities is happening much faster than expected. The most dramatic sign is a sudden acceleration of the rate of shrinkage of Arctic sea ice.

Prominent NASA climate scientist Dr James Hansen is perhaps the most vocal, but far from alone, in arguing that the Earth may be very close to a tipping point beyond which large, unstoppable and irreversible climate change could occur.

Scientific issues are not settled by appeals to authority, nor by a vote. That is not the issue here. The issue is whether scientists’ professional judgments have weight.

Those in strategic positions in our society, like politicians and journalists, who treat scientists’ collective professional judgments as no better than any other opinion are being seriously irresponsible.

You can ignore the IPCC if you want, but you should realise that its most recent assessment may have seriously understated the global warming problem. You can ignore James Hansen if you want, but you should know that his judgments from two or three decades ago are being broadly vindicated.