IPCC pulls numbers out of thin air

It seems the world has long been on the verge of disaster.  In the 1970s The Club of Rome predicted the imminent end of raw materials, while climatologists warned of global cooling.  Writing in these pages Peter Cebon and James Risbey ask the question how certain we need be about global warming before taking action.  Hopefully, more certain than we were about global cooling just 30 years ago.  The Intergovernmental Panel on Climate Change (IPCC) published its Summary for Policymakers in February this year.  We're told there is a "very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming".  The IPCC is 90 per cent confident humans are responsible for global warming.  Its level of scientific understanding of greenhouse gases is "high".  The IPCC admits its level of scientific understanding of alternative theories is "low", but confidently informs us that these alternatives do not contribute much to global warming.

There are legitimate difficulties with the IPCC's 90 per cent confidence in anthropogenic warming.  It is not ludicrous to question what that number means.  The IPCC seems to imply that this number results from a scientific process -- that it has tested a hypothesis.  Indeed, the IPCC tells us its understanding is based "upon large amounts of new and more comprehensive data, more sophisticated analysis of data, improvements in understanding of processes and their simulation in models, and more extensive exploration of uncertainty ranges".  If this is what the IPCC has done, it has very weak evidence.  Ninety per cent is the weakest acceptable level of confidence in a hypothesis test.  It is not clear from the Summary whether the IPCC has, in fact, undertaken such an analysis.  It is more likely that it has neither a testable model nor data available for external researchers to replicate such a test.  In other words, the IPCC's 90 per cent confidence has emerged from scientists evaluating whether they think their own work is correct.

There is an even greater problem with the analysis.  The IPCC provides a breakdown of seven extreme weather events, and an assessment of human influence on those events.  Only two of the individual events have a human impact of at least 66 per cent, the other five are 50-50 propositions.  Somehow this all adds up to 90 per cent.  Furthermore, in three of the weather events there is no underlying human attribution study -- the IPCC made up that data.

Nobody is suggesting that we despoil the planet and leave an environmental mess for future generations.  The IPCC, however, indicates the very real limits of our knowledge and -- understanding of climate change.  Given this lack of knowledge and understanding of climate change it is not unreasonable for policymakers to adopt a cautious approach to policy change.  It is also not unreasonable for people to discount the hysterical commentary around climate change.

ADVERTISEMENT