October 10, 2005

Sea Level Rise: How High?

Filed under: Climate Models, Sea Level Rise

Global sea level rise figures prominently in most climate doom and gloom stories. And, not surprisingly, good news is either ignored or mis-reported.

First, a little history. The Intergovernmental Panel on Climate Change estimated, in its Third Assessment Report (2001), that between 1990 and 2100, the global average sea level will rise somewhere between 3.5 and 34.6 inches, with a central value of 18.9 inches. Of course, the values falling near the low end of the range are usually left out of global warming scare stories, while the values near the high end are prominently featured (e.g. see here and here).

A couple of recent modeling studies demonstrate that those who have said that estimates near the low end of the UN’s huge range (i.e., us) are probably right. Using the high resolution version of the climate model developed at the Center for Climate System Research at the University of Tokyo run with two different IPCC emissions scenarios (resulting in atmospheric carbon dioxide concentrations of 550 and 720ppm by 2100), a research team led by Tatsuo Suzuki found that global average sea levels by 2100 were projected to rise by somewhere around 12 inches (in the 550ppm scenario) and 15 inches (in the 720ppm scenario). The warming projected to accompany the 15-in. sea level rise in the 720 ppm scenario (SRES A1B) was about 4.0ºC.

sea level rise

Figure 1. Components of sea level rise as projected by the Japanese climate model run under two different IPCC emissions scenarios. Add up the contributions from expansion (steric rise) and from Greenland and Antarctica, and you get between 12 and 15 inches (30 and 38 cm) by the end of this century.

Another modeling study found about the same thing. Although the details are a bit sketchy, a press release from the Max Planck Institute for Meteorology, touts that scientists using the latest-greatest version of the Max Planck climate model project a global average sea level rise of about 12 inches (30 cm) in association with a temperature rise of 4ºC by 2100. From what we can gather from the press release, this occurs when the climate model is input one of the IPCC high CO2 emissions scenarios. The Max Planck modelers also used more moderate emissions scenarios, but these results were not reported in the press release for reasons that should be obvious (no problem=no funding).

Since the upward trend in global averaged temperatures that has been well-established for about the past 30 years is about 0.18C per decade (and there is a new paper suggesting that solar variability has been responsible for about 10-30% of that, see here), a rise of 4ºC in the next 100 years as a result of anthropogenic alterations to the earth’s atmospheric composition is just too much.

The central tendency of the consensus of climate models is that, once warming starts as a result of human influence, it takes place at a constant (not an increasing) rate. So, 1.8°C/century, at the max, is what we can expect (i.e. ten times 0.18°). Since the sea level rise is closely tied to the temperature rise, even the modest 12-15 inch projections from the most-current climate models, are also on the high side.

Thus it appears that the demand for policy actions to reduce greenhouse gas emissions has lost another of piece of its foundation—the threat from a rapidly rising ocean. After all, a future sea level rise on the order of a foot or so by the end of this century hardly seems bad enough to jolt people into lifestyle-altering action, especially considering that over the last century, the sea level rose by about one-half to two-thirds that amount, and coastal development boomed.


Max Planck Society press release, Climate Change More Rapid Than Ever, September 30, 2005.

Suzuki, T., et al., 2005. Projection of future sea level and its variability in a high-resolution climate model: Ocean processes and Greenland and Antarctic ice-melt contributions. Geophysical Research Letters, 32, doi:10.1029/2005GL023677.

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