James Hansen: Scientific reticence and sea level rise

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http://www.iop.org/EJ/article/1748-9326/2/2/024002/erl7_2_024002.html

IOP Electronic Journals
Environmental Resarch Letters
The open-access journal for environmental science


Scientific reticence and sea level rise

J E Hansen

NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA

Received 23 March 2007
Accepted 3 May 2007
Published 24 May 2007

I suspect the existence of what I call the `John Mercer effect'. Mercer (1978) suggested that global warming from burning of fossil fuels could lead to disastrous disintegration of the West Antarctic ice sheet, with a sea level rise of several meters worldwide. This was during the era when global warming was beginning to get attention from the United States Department of Energy and other science agencies. I noticed that scientists who disputed Mercer, suggesting that his paper was alarmist, were treated as being more authoritative.

It was not obvious who was right on the science, but it seemed to me, and I believe to most scientists, that the scientists preaching caution and downplaying the dangers of climate change fared better in receipt of research funding. Drawing attention to the dangers of global warming may or may not have helped increase funding for relevant scientific areas, but it surely did not help individuals like Mercer who stuck their heads out. I could vouch for that from my own experience. After I published a paper (Hansen et al 1981) that described likely climate effects of fossil fuel use, the Department of Energy reversed a decision to fund our research, specifically highlighting and criticizing aspects of that paper at a workshop in Coolfont, West Virginia and in publication (MacCracken 1983).

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The nonlinearity of the ice sheet problem makes it impossible to accurately predict the sea level change on a specific date. However, as a physicist, I find it almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale. The threat of a large sea level change is a principal element in our argument (Hansen et al 2006a, 2006b, 2007) that the global community must aim to keep additional global warming less than 1 °C above the 2000 temperature, and even 1 °C may be too great. In turn, this implies a CO2 limit of about 450 ppm, or less. Such scenarios are dramatically different than BAU, requiring almost immediate changes to get on a fundamentally different energy and greenhouse gas emissions path.

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Almost four decades ago Eipper (1970), in a section of his paper titled `The Scientist's Role', provided cogent advice and wisdom about the responsibility of scientists to warn the public about the potential consequences of human activities. Eipper recognized sources of scientific reticence, but he concluded that scientists should not shrink from exercising their rights as citizens and responsibilities as scientists. Climate change adds additional imperative to Eipper's thesis, which was developed with reference to traditional air and water pollution. Positive climate feedbacks and global warming already `in the pipeline' due to climate system inertia together yield the possibility of climate `tipping points' (Hansen et al 2006b, 2007), such that large additional climate change and climate impacts are possible with little additional human-made forcing. Such a system demands early warnings and forces the concerned scientist to abandon the comfort of waiting for incontrovertible confirmations.

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