Warming Likely to Have Modest Effect on Sea Level, If Any

Published January 1, 2006

One of the great fears generated by global warming is that the oceans are about to rise and swallow our coasts. These concerns have been heightened by the substantial uptick in Atlantic hurricane activity that began in 1995.

The frequency of really strong storms striking the United States now resembles what it was in the 1940s and ’50s, however, which few people (aging climatologists excepted) remember.

Little Recent Change

Those who argue global warming is an overblown issue have been claiming for years that “consensus” forecasts of sea level are equally overwrought. The United Nations’ Intergovernmental Panel on Climate Change predicts a global average rise of from 3.5 to 34 inches by 2100, with a central estimate of 19 inches. Depending upon how you slice or dice the data, the last century saw a rise of maybe six inches.

Critics of this position have long argued that the predicted changes would require a substantial net melting of some combination of the world’s two largest masses of land-based ice–Antarctica and Greenland. In addition, they note that observed global warming is right near the low end of the UN’s projections, which means the realized sea level rise should be similarly modest.

Antarctica Not Melting

Over 15 years ago, John Sansom, who was with the New Zealand Meteorological Service at Wellington, New Zealand at the time, published a paper in the Journal of Climate that examined the prior 30 years of Antarctic temperature data and showed no net warming of Antarctica during that time period. While it was widely cited by critics of global warming doom talk, no one else seemed to take notice. After all, it relied on only a handful of stations. Then, in 2002, University of Illinois at Chicago researcher Peter Doran published a more comprehensive analysis in Nature and found a cooling trend.

At the same time, a deluge of stories appeared, paradoxically, about Antarctic warming. These studies concentrated on the tip of the Antarctic Peninsula, the narrow strip of land that juts out toward South America. That region, which comprises less than one-half of one percent of Antarctica, is warming because the surrounding ocean has warmed.

Warmer water, however, evaporates more moisture, and the colder the land surface over which that moisture passes, the more it snows. So, Antarctica as a whole should gain snow and ice.

That has been confirmed. Last year, C.H. Davis published a paper in Science about how this accumulating snowfall over eastern Antarctica was reducing sea level rise. This year, Duncan Wingham, at the 2005 Earth Observations summit in Brussels, demonstrated the phenomenon is being observed all over Antarctica.

Greenland Signals Mixed

The situation in Greenland is more complex. In 2000, William Krabill estimated the contribution of Greenland to sea level rise at 0.13 mm per year, or a half an inch per century. That’s not very different from zero. In October, using satellite altimetry, O.M. Johannessen published a remarkable finding in Science that the current trend in Greenland ice is a gain of 5.4 cm (two inches) per year.

Almost all of the gain in Greenland has been in areas greater than 5,000 feet in elevation (which is most of the place). Below that, there has been glacial recession. It shouldn’t be lost on anyone that because no one ventures into the hostile interior of Greenland, all we see are pictures of the receding glaciers near the coast!

The temperature situation in Greenland is more mixed than in Antarctica. Over the last 75 years, there has been cooling in the southern portion (where the recession has been greatest) and some warming in the North.

Other Glaciers Not Significant

The only other masses of ice on the planet that can contribute to sea level rise are the non-polar glaciers, but they are very few and far between. The biggest is the Himalayan ice cap, but it’s so high that a substantial portion will always remain. Most of the rest are teeny objects tucked away in high-elevation nooks and crannies, like our Glacier National Park.

If all these glaciers–including the Himalayan ice cap– melted completely, sea level could rise no more than five to seven inches, because there’s just not that much mass of ice.

Science Rebuts Media Scares

It is simply impossible for the scientific community to ignore what is going on, even as prone to exaggeration of threats as it has grown to be.

The planet is warming at the low end of projections. Antarctica is undoubtedly gaining ice, not losing it. Greenland may be losing a little ice or, as shown in the recent Johannessen study, gaining ice dramatically. Clearly, it is going to take quite some time before melting ice can make the oceans rise much, if at all.

Computer models, while still shaky, are now taking account of this reality. Every one of them now says Antarctica will contribute negatively to sea level rise in the next century, while almost every model now has Greenland’s contribution as a few inches, at best.

It is inevitable that one of tomorrow’s headlines will be that scientists have dramatically scaled back their projections of sea level rise associated with global warming. Had they paid attention to data (and snow) that began accumulating as long as 15 years ago, they would never have made such outlandish forecasts to begin with.

Patrick Michaels ([email protected]) is former president of the American Association of State Climatologists and is a senior fellow for environmental studies at the Cato Institute. This article appeared earlier on the Cato Institute Web site, http://www.cato.org.