Dr. James Hansen
In 2005, I argued that ice sheets may be more vulnerable than the Intergovernmental Panel on Climate Change (IPCC) estimated, mainly because of effects of a warming ocean in speeding ice melt. In 2007, I wrote “Scientific Reticence and Sea Level Rise,” describing and documenting a phenomenon that pressures scientists to minimize the danger of imminent sea level rise.
About then I became acquainted with remarkable studies of geologist Paul Hearty. Hearty found strong evidence for sea level rise late in the Eemian to +6-9 m (20-30 feet) relative to today. The Eemian is the prior interglacial period (~120,000 years ago), which was slightly warmer than the present interglacial period (the Holocene) in which civilization developed. Hearty also found evidence for powerful storms in the North Atlantic near the end of the Eemian period.
It seemed that an understanding of the late Eemian climate events might be helpful in assessing the climate effects of human-made global warming, as Earth is now approaching the warmth that existed then. Thus several colleagues and I initiated global climate simulations aimed at trying to understand what happened at the end of the Eemian and its relevance to climate change today.
More than eight years later, we are publishing a paper describing these studies. We are publishing the paper in an open-access “Discussion” journal, which allows the paper to become public while undergoing peer-review (a pdf of the paper with figures imbedded in the text for easier reading is available here). I will get to the reasons for that in a moment, but first let me mention some curious numerology to get you thinking about scientific reticence.
Did you read any of the recent papers that concluded ice sheets may be disintegrating and might cause large sea level rise in 200-900 years? The time needed for ice sheets to respond to climate change is uncertain, and there are proponents for time scales covering a huge range. However, 200-900 years should cause a scientist to scratch his head. If it is uncertain by an order of magnitude or more, why not 100-1000? Where does the 200-900 precision come from?
Why the peculiar 900 years instead of the logical 1000? Probably because nobody cares about matters 1000 years in the future (they may not care about 900, but 200-900 does not seem like infinity). A scientist knowing that sea level is a problem does not want the reader to dismiss it.
Why 200 years? For one thing, 100 years would require taking on the formidable IPCC, which estimates that even the huge climate forcing for a hypothetical 936 ppm CO2 in 2100 would yield less than one meter sea level rise. For another thing, incentives for scientists strongly favor conservative statements and militate against any “alarmist” conclusion; this is the “reticence” phenomenon that infects the sea level rise issue2. “Scientific Reticence and Sea Level Rise” will be the subject of a session at the American Geophysical Union meeting this year.