What Lies Beneath: The Understatement of Existential Climate Risk

By David Spratt & Ian Dunlop, pub. by Breakthroughonline.org.au, National Centre for Climate Resoration, Melbourne, Australia, 2017.

What Lies Beneath by David Spratt & Ian Dunlop is a brief (40 page) report prepared by the National Centre for Climate Restoration (also called Breakthrough), an Australian think tank dedicated to climate restoration. The report is organized in three sections: Risk Understatement, Scientific Understatement, and Political Understatement. Each section comprises a series of 1 – 3 page overviews of specific topics that highlight that section’s thesis. Noted climate expert Joachim Schellnhuber wrote the book's Foreword.

The Risk Understatement section focuses on the definition of risk and how it shapes our response to global climate change. Specifically, although extreme events (e.g. ice sheet collapses, permafrost feedbacks, and other tipping points) are unlikely, their impact is very large. Thus, since risk is the product of likelihood and impact, the risk from such extreme events is high and is often underestimated within both the public and scientific communities.

The Scientific Understatement section suggests that the scientific community is underestimating global climate change. For example, semi-empirical climate models often suggest larger changes in the global temperature relative to fully-coupled models. Likewise, the current climate sensitivity (change in global temperature occurring if greenhouse gases doubled in concentration) estimate of 3°C suggested by the IPCC report may be too low by not accounting for changes in climate sensitivity as the Earth warms. Additionally, sea-level rise has historically followed the highest IPCC projections instead of the mean projection. Using this evidence, Spratt and Dunlop suggest that scientists are being too cautious and underestimating the impact of global warming.

The final section, Political Understatement, focuses on the need for consensus and timescale of the IPCC report generating process. By requiring consensus, the report is necessarily more conservative in estimating risk. Moreover, the long timescale associated with generating the report often leads to exclusion of the most recent data. Based on these arguments, Spratt and Dunlop advocate a very rapid decrease in global carbon emissions.

This report is freely available (https://www.breakthroughonline.org.au/whatliesbeneath) and worth reading in that it reframes the actual risk of global climate change by noting that even unlikely events pose a major risk due to their large impact. Moreover, the report includes extensive citations, allowing for further exploration. The only criticism of this report is that the “fat-tail” of the probability distribution generated by climate models is highly susceptible to model parameters. Similarly, the impact of extreme events also has a large degree of uncertainty. Thus, the risk of such events is difficult to accurately estimate. Regardless, What Lies Beneath is an excellent addition to the climate change discussion.

Manish Gupta, PhD
manish.gupta@gmail.com

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.