Global warming: Beyond a reasonable doubt

  1. Roast, or idle boast?

2. Ultimate cooker

3. See rising sea level

4. Know for sure?

5. What to do?


Soggy predictions
Curiously, a major prediction about global warming concerned the ocean, not the atmosphere: Melting glaciers and warming water would raise sea levels, threatening coastlines that are home to huge numbers of people.

Looking soggy, dirty and half-collapsed, the glacier towers over the camera.
The front of a melting glacier. Courtesy Giuseppe Zibordi, Michael Van Woert, NOAA NESDIS, ORA.

Measurements show that sea level has risen about 15 centimeters over the past century.

Climatologist Kevin Trenberth notes that while predictions for sea level have changed over the years, rising seas remain "a major problem on long-time scales.... Even if you stabilize temperature and greenhouse gases, sea level will continue to rise."

Watery and grave
Low-lying atolls in the Pacific and Indian Oceans are already threatened. The first environmental refugees of the greenhouse century could come from a place like the Carteret (or Tulun) islands of Papua New Guinea.

The island's 1,400 residents say the rising sea has polluted their gardens with salt water, and they may starve even before the sea inundates their homes. The residents have applied for relocation money, but the government says it lacks the cash.

map of south pacific, highlighting Papua New Guinea and Tuvalu

Rising seas also endanger the Pacific nation of Tuvalu, which may sue the developed world that creates most greenhouse gas pollution. The David-and-Goliath lawsuit would be hard to win, but it could raise the profile of island flooding.

Even small sea rises could have enormous effects, Trenberth points out, since a storm surge at high tide can produce severe damage. The 1998 El Nino in California, he says, cause "a tremendous amount of erosion, houses toppling into ocean. It was a real indicator of the type of thing you would expect to see with rising sea level."

In general, Trenberth says, sea level rise "is not a gradual process. It's not that you wait and gradually the sea trickles up and covers your toes. ... it happens in episodic fashion, for the most part you may be fine, but in a tropical storm, a whole island can be inundated. ...Some of these nations could disappear overnight."

The unfrozen continent
Because so much water is stored in Antarctica, concern over rising sea levels inevitably causes a glance to the south, and the news has been ominous. Last March, a section of ice as big as Rhode Island broke away and disintegrated, stunning glaciologists.

All the estimates rise, more or less steeply. By 2100, the rise could equal 0.2 meters to 0.8 or so.
Estimates for sea-level rise show the effects of various scenarios for economic and technological development. IPCC Climate Change 2001, Technical Summary, Working Group I, 2001, p. 74.

By itself, this breakup will not raise sea level, since floating ice does not raise sea level when it melts. However, ice surrounding the continent helps restrain ice in the interior, which may flow more quickly toward the ocean.

A big melting in Antarctica could cause a huge rise in sea level, but since other parts of the continent are cooling, the overall message is confusing.

Slowly and steadily, sea level is rising. It's more evidence of global warming. Greenland's white cap
We've just gotten disturbing evidence from Greenland. About 10 percent of Earth's fresh water is locked in a giant icecap there. This June, NASA scientists reported that the icecap is rapidly melting.

Because ice conducts little heat, experts had expected the icecap to respond slowly to warming. But meltwater from the surface is seeping through cracks and lubricating the rock below.

"Previous models suggested that it might take hundreds, even thousands of years for changes in an ice sheet's surface to be felt at the base," NASA glaciologist H. Jay Zwally told the Atlanta Journal and Constitution. "This shows that summer melting can accelerate the ice flow in a matter of weeks" (see "Glacial Melt ..." in the bibliography).

Rising seas. Hot temperatures. Is this global warming?

It looks like hot duck. It smells like hot duck. Is it roast duck?




  The Why Files  

There are 1 2 3 4 5 pages in this feature.
Bibliography | Credits | Feedback | Search

©2002, University of Wisconsin, Board of Regents.