THE SCIENCE

“Now that most scientists agree human activity is causing Earth to warm, the central debate has shifted to whether climate change is progressing so rapidly that, within decades, humans may be helpless to slow or reverse the trend.”
Juliet Alperin, The Washington Post, January 29, 2006

When approaching this project, we wanted to address the potential reality of global warming hitting home. We mapped the route of the walk based on looking at areas of Seattle's downtown that are less than 20 feet above sea level. Estimates of potential sea level rise due to global climate change range from just a few inches to 80 feet or more. We based this project on a twenty-foot sea level rise, which is most famously documented in the movie 'An Inconvenient Truth.' The twenty foot sea level rise is the amount of sea level rise that would occur if either of the world’s major ice sheets – the Antarctic Ice Shelf and the Greenland Ice Shelf – were to melt.

Dramatic sea level rise is one of the tipping points related to climate change that most concerns scientists. Such a sea level rise would take place in a relatively short period of time (a century or two), tens of thousands of years to reverse, and adaptation would be difficult, in particular for the estimated 634 million people who live near coastlines (McGranahan et al, Environment and Urbanization, 2007). Together, these ice sheets also hold nearly 20 percent of the world’s fresh water.

When we might reach this point is unclear. Current measurements have shown much higher rates of ice sheet melting than models have predicted, and once the reflective surface of the ice is replaced by the heat-absorbent surface of water or earth, melting will only accelerate.

The dramatic changes in sea level that would be caused by the melting of the ice sheets has been a benchmark in climate change science since 1978, in an article in the journal Nature. These findings were extensively reviewed in the 1983 National Research Council study, Changing Climate, the first comprehensive assessment of science and policy pertinent to the global warming problem.

James Hansen is director of the Goddard Institute for Space Studies at NASA, and has been repeatedly harassed by the Bush Administration for his outspoken views on climate change. A shorter article by Hansen (citation below) puts the sea level rise at 80 feet with a temperature rise of 2-3 degrees Fahrenheit, which would melt ice on Greenland, the West Antarctic Ice Shelf, and the East Antarctic Ice Shelf.

The International Panel on Climate Change (IPCC), a group of hundreds of climate scientists from around the world, have estimated a 7-23 inch sea level rise by the end of the century. However, those estimates have been widely acknowledged to be conservative, both because the IPCC functions by consensus, because their conclusions are the basis for policy and are thus politically charged, and also because the IPCC scientists themselves are appointed by their countries’ respective political leadership. Further, the IPCC’s estimates do not take into account any of the positive feedback loops, such as ice sheet melt, that would mean rates of climate change and sea level rise that go far beyond current projections.

A group of scientists and the University of Washington’s Climate Impacts group attempted to estimate the potential for sea level rise in Northwest Washington, from Puget Sound to the Olympic Peninsula. These estimates accounted for sea level rise from thermal expansion (water expands as it warms) and ice sheet melt, local variation in wind (which affects sea level), and local changes in land levels (uplift at the western edge of the continental plates as one plate slides under the other). Although less conservative than the IPCC estimates in that they attempted to predict ice sheet melt, these estimates are based on current science, and therefore did not attempt to take into account the potential for positive feedback loops discussed above. The report concludes that in Puget Sound local sea level rise will closely match global sea level rise. Estimates of sea level rise in 2100 range from 6 to 50 inches.

Other resources:
Oppenheimer, Michael (2005). “Ice Sheets, Global Warming, and Article 2 of the UNFCCC,” (with R.B. Alley), Climatic Change 68, 257-267.
Oppenheimer, Michael (2004). “The West Antarctic Ice Sheet and Long Term Climate Policy,” (with R.B. Alley), Climatic Change 64, 1-10.
Hansen, James: 2004, ‘Defusing the Global Warming Time Bomb’, Scientific American 290, 68–77.
Hansen, James: 2005, ‘Slippery Slope: How Much Global Warming Constitutes “Dangerous Anthropogenic Interference”?’, Climate Change 68, 269–279.
Hansen, James (2006). ‘Can We Still Avoid Dangerous Human-Made Climate Change?’ Social Research: An International Quarterly of Social Sciences Vol 73, No 3, 949 – 974.