Why listen to scientists?

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.