TCS Daily


Level With Me

By Willie Soon - November 1, 2002 12:00 AM

"We're talking of about the submergence of islands, submergence of Shanghai, the submergence of Bombay, the submergence of New York City... Manhattan would be under water."
- Greenpeace climate policy director Steve Sawyer.
"Scientists estimate that by the year 2040 sea level might rise from two inches to one foot higher than today. If it rises one foot, a major storm surge would push the Potomac River over its banks, flooding the park along the river and the Reflecting Pool. The Jefferson Memorial would become an island. By the year 2075, sea level might rise from four inches to two feet higher than today. If it rises two feet, a major storm surge would nearly encircle the Washington Monument and completely surround the Internal Revenue Service, the National Museum of Natural History, the National Gallery of Art and neighboring structures. Muddy waters would even reach the grounds of the U.S. Capitol."
- Dr. Janine Bloomfield, Environmental Defense Fund
The implications of these comments are obvious. If we don't stop emitting lots of greenhouse gases, the planet will heat up. If the planet heats up, sea levels will rise. And if sea levels rise, say goodbye to New York, Washington, Shanghai, Bombay, and other major global cities. So let's get to work on reducing greenhouse gas emissions.

Such claims are common enough these days. Recently a very distinguished physicist warned of a rise in the level of Lake Michigan by 100 meters over two years, so that most of Illinois would be covered with saltwater while only tenants above 30th story of the Sears Tower could be spared. The physicist went on to suggest that "[m]aybe the worriers about global warming have a point."

But do they? Just because claims are commonly made - or alarming - doesn't necessarily mean they're true. So let's see what the science tells us.

Perspective

In order to assess these claims, it's useful to remember that our current understanding of global warming and sea-level change is still full of scientific uncertainties and unknowns. As such, even if we are able to arrive at some firm conclusions - say, that there have been detectable changes in temperature or sea level - knowing precisely what caused those changes may be difficult to apprehend.

The current best-available records show that the sea level may be rising a rate of 1-3 mm per year. That would yield a grand maximum increase of 300 mm per century.

Now, let's put that in perspective. Such a rate of sea-level increase is small when compared to the rapid rise of 990 mm per century known to occur between 15,000 and 6,000 years ago. At that time, the ice sheets from the last ice age melted due to natural causes and reactions.

It is important to note that the large sea-level rebound from the last ice age is still being played out in the seacoasts around the world today. Continental and marine ice sheets, the land and earth's crust, terrestrial water catchment reservoirs (both natural and anthropogenic), oceans and climate are all readjusting to distribute the spread of water on Earth.

Despite the enormous complexity of this process, and the limits of our scientific understanding of many of the factors that contribute to the accounting of sea-level changes all over the world, some scientists and politicians continue to alarm the public to the most extreme scenarios - however improbable they may be.

Alarmism

One example of this alarmism comes from the United Nations Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report's (TAR) Technical Summary (TS), published in 2001. It warns of a probable tragic global sea level rise 1000 years from now (Figure 1).



This figure [from p. 77] outlines the consequences due to a warming scenario of 3, 5.5, and 8 degrees Celsius. According to the IPCC, these warming scenarios would shrink the Greenland ice sheet and prompt a rise in sea level.

For example, a warming of 8 Celsius would occur under an (improbably high) concentration of CO2 of 8 times the present level, or about a 1.5% per year increase. Such an increase - and the resultant warming in the IPCC models - will lead to an almost complete melting of the Greenland ice sheet. According to this scenario, Greenland would melt away three-quarters of its ice sheet volume and shrink its ice area to 30% of the present-day value. And the melting would cause an increase of the current global sea level by almost 600 cm (or 6 meters) by the year 3000.

Such a rise would, indeed, be troubling. Unfortunately for the alarmists, there are several important natural changes of sea level unaccounted for in this scenario. Indeed, these background natural changes are not considered by any of the UN IPCC's global warming model future scenarios.

How large are some of these natural modes of sea level change? Around the Baltic Sea, for instance, the sea level is actually falling at a rate as rapid as 10 mm per year - 1000 mm per century. Places like Alaska and Scandinavia are still experiencing land uplifts due to an ongoing rebound from the last ice age. Areas around Japan, Papua New Guinea and New Zealand are facing non-glacial uplifts - or subductions - related to movement in the Earth's crust. Experts on the Indian Ocean suggested the observed inter-decadal variability of sea level along the Indian coast can be linked more directly to a major climatic aspect of the region - variability of monsoon - than simple warming and expansion of the upper ocean waters in climate models.

A Growing Antarctica



Now look at the figure above, Figure 2, which shows the response of the Antarctic ice sheet to global warming and its contribution to global sea level variation over the same period of time as the IPCC report. Scenarios labeled 'low' (2XCO2), 'mid' (4XCO2) and 'high' (8XCO2) represent the same cases in Figure 1 where the added carbon dioxide caused a warming of 3, 5.5 and 8 Celsius by the year 2130. Negative values mean a drop in the global sea level. The case labeled 'ant_con' is a background case with no CO2 forcing. [From Huybrechts and Wolfe, Journal of Climate, 1999.] Now Figure 2 offers an interesting illustration that was left out in the 2001 IPCC report. Figure 2 shows the simultaneous contribution of the Antarctic ice sheet to the global sea level rise results in Figure 1. In the case of the Antarctic ice sheet, Figure 2 demonstrates that some warming scenarios can lead to a relatively large net accumulation of ice on the Antarctic continent and hence contributing to a drop in the global sea level.

Now turn your attention to Table 1 below. This is the predicted range of the Greenland and Antarctic contributions to global sea level change by the year 2100 for the same three carbon dioxide-global warming scenarios as in Figures 1 and 2 [From van der Veen , Global and Planetary Change, 2002]. Negative values mean sea-level fall while positives meant sea-level rise.

Future Scenario Greenland Antarctica Combined
Low (2XCO2) 2.7 to 4.9 cm -5.6 to -3.0 cm -2.2 to 1.2 cm
Mid (4XCO2) 7.3 to 13.5 cm -10.4 to -5.6 cm -1.6 to 6.3 cm
High (8XCO2) 14.5 to 27.0 cm -14.8 to -8.0 cm 2.2 to 16.4 cm


The author of this recent scientific analysis noted that if the highly unlikely scenario of 8 Celsius global warming (by the year 2130) can be ruled out, then a net sea level lowering by the year 2100 is as likely a mathematical possibility as a sea level rise.

In other words, no scientific case can even be made to predict a global sea level rise due to CO2-induced changes in the Greenland and Antarctic ice sheets. That's what explains the IPCC extending its climate model 50 generations into the future, instead of the more typical five generation future projection. The IPCC's interest was not in informing the public of the relevant available science. Rather it was in generating a scare scenario of a melting Greenland ice sheet, despite the well-known geological evidence demonstrating that the Greenland ice sheets have been stable for at least the last few interglacial periods - about a few hundred thousand years.
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