The International Panel on Climate Change (IPCC) relies substantially on three areas of evidence to show that humans are having a significant influence on climate (global warming).
Professor Gabi Hegerl
Models. These simulations, or illustrations, based on what we know, show a possible trend of global warming. As time passes, there is the potential to check these illustrations against what actually happens to the global temperature - though it is necessary to bear in mind that the background climate is liable to fluctuate from causes quite unrelated to human activity. It should also be said that the climate system is incredibly complex and many scientists consider climate science in its infancy. The reliability of models in such a complex environment requires rigorously validation.
Eliminating natural processes. Climatologists seek to show that the increases in temperature cannot be accounted for by any other known natural process. The complexity referred to above, and the unknowns to which it gives rise, to are also relevant in this line of argument.
Prof Geoffrey Boulton
Paleoclimate studies. Studies of tree rings and other 'proxies', indicators of temperatures have been used to show that the current warming is unprecedented. The implication is that current warming is not only more likely to be largely human in origin, but that the consequences, taking us into unprecedented territory, are potentially dangerous to the planet and humanity and requiring drastic changes in public policy.
This last argument has been one feature of recent controversies, including 'Climategate'. Scientists in Edinburgh have featured in the debate which has raged in peer reviewed papers, the blogs and in the enquiries into 'Climategate'.
Professor Tom Crowley
First, the scientists. Sustained criticism of the quality (and reliability) of the tree ring studies, which purport to show that recent warming is unprecedented and on which the third line of evidence is largely based, has led to a rash of peer reviewed papers claiming that current temperatures are warmer than the Medieval Warm Period (MWP).
Hegerl is married to Professor Tom Crowley who himself has been accused of trying to do away with the MWP eg here. Then there is Professor Simon Tett who appeared less frequently in the leaked Climategate correspondence than Hegerl and Crowley. He is the head of the Centre for Earth System Dynamics at Edinburgh University. All three came to Edinburgh University in 2007.
Another key player is Professor Geoffrey Boulton who is General Secretary of the Royal Society of Edinburgh and Regius Professor Emeritus and former Vice Principal of the University of Edinburgh. He has been an influential public policy advisor and played a key role in the Russell Review. This enquiry was charged with examining the leaked emails from the Climatic Research Unit to enquire if there had been scientific practise or anything which called into question the research outcomes. One critique of the Russell Review was the subject of this blog's first post three weeks ago.
Currently, all four appear to to be staunch defenders of paleoclimate studies for its contribution to the case that recent warming is unprecedented. And they seem to maintain this position in the face of growing evidence that the discipline has produced little to support the case for human induced global warming. Professor Hegerl was herself a co-ordinating lead author for the IPCC Fourth Assessment Report Working Group 1 on 'Understanding and Attributing Climate Change'.
It is difficult to comprehend how the establishment, (which the Edinburgh four represent), have chosen to deal with challenges to their assumptions and authority. The Independent Climate Change Email Review has hardly contributed to enhancing confidence in the work of CRU or paleoclimate studies. Rather the opposite is the case, mainly because of the rather obvious partisanship with which it undertook its task. A frank admission of evident failings within the community would go a long way to begin to allow confidence in scientific endeavour to be reasserted.
There are many other aspects to the evidence for the warming of the planet and its significance. The way tree ring and similar proxy studies have been used and defended does not inspire confidence that the debate is being conducted on the basis of reliable evidence. Public policy on climate depends to a significant extent on the IPCC reports. Public confidence in its description of the scientific evidence has fallen in recent months.
If public confidence in climate science is to be regained then the criticisms must be fairly addressed, not ignored or dismissed.