October 19, 2000

A World on Thin Ice?

Global Meltdown  

Scientists traveling near the North Pole on a Russian icebreaker in August were shocked when the ship reached a mile-wide stretch of open water—the first ever confirmed sighting of liquid ocean at the North Pole. What's happening to the Arctic ice cap, and what are the consequences?

Scientists say that water last covered the North Pole more than 50 million years ago. When one Harvard University oceanographer visited the North Pole 6 years ago, the ice cap—the ice above the water's surface—was 1.8 to 2.7 meters (6 to 9 feet) thick. He was shocked to see liquid water there this summer.

The Arctic ice cap covers an area roughly the size of the United States, but it is shrinking dramatically. Each year since 1978, the ice cap has lost an average of 33,800 square kilometers (13,000 square miles)—an area the size of Massachusetts and Connecticut combined. Measurements made by submarines show that the average thickness of the cap decreased from 3 meters (10 feet) thick during the 1960s to 1.8 meters (6 feet) in the 1990s.

  • How many square kilometers (or square miles) has the ice cap lost in the 22 years since 1978?

  • By what percentage has the thickness of the ice decreased from the 1960s?

Data collected on the thickness of the ice below the surface—known as "sea ice draft"—paints a similar picture. Recently, researchers compared data collected in the mid-1990s with data gathered from the 1950s to 1970s. They were startled to find that Arctic sea ice draft had decreased by 1 meter (3 1/2 feet) since the earlier time period.

The graph below compares the sea ice draft at various Arctic locations. The reduction of thickness at all the measured points shows that the melting ice in the Arctic is widespread.

  • Estimate the percentage decline of sea ice draft from 1958-1976 (blue bars) to 1993-1997 (red bars) in each of these Arctic regions: Chukchi Cap, Beaufort Sea, Canada Basin, North Pole, and Eastern Arctic.

  • Which region had the greatest percentage loss?

  • What was the percentage decline for all regions?

Antarctica, which contains about 90% of Earth's ice, is melting too. So far, most of the melting has been at the continent's edges. Icebergs as large as Delaware have broken off Antarctica in recent years, threatening ships in the open water. In September, an iceberg 48 kilometers (30 miles) long and 18 kilometers (11 miles) wide separated from the Antarctic continent.

The Warming Earth  

The planet's melting ice and snow is one symptom of global warming. Over the past century, Earth's surface warmed by an average of about 1° F. It doesn't sound like much. But this relatively modest warming has brought havoc to the world's cryosphere, its snow and ice environments.

The evidence for global warming grows with each passing month. A recent study of ice-core samples taken high in the Himalayas reveals that both the last decade and the last 50 years were the warmest in 1,000 years. In fact, the twentieth century's 10 warmest years all occurred since 1985, and 1998 was the warmest year on record.

Some computer models predict an additional rise of 5 to 10 degrees F over the next century. To put that number in perspective, the Earth is now an estimated 5 to 9 degrees warmer than it was in the last ice age about 18,000 to 20,000 years ago. At that rate, scientists worry that the biosphere will change faster than thousands of threatened species can adapt or migrate. Large scale extinction of plants and animals would be the sad result.

  • Look at the graph of average global temperature change from 1861 to 1996. The y-axis shows the amount that temperature was greater or less than a baseline value.

  • Calculate how much average global temperature has increased since: a. 1901 b. 1921 c. 1941 d. 1961 e. 1981

  • Which twentieth century decade was the warmest?

  • How does the rate of temperature change in the nineteenth (from 1861 onward) and twentieth centuries compare?

Global sea level rose by 10 to 25 centimeters (4 to 10 inches) over the last century. Melting ice caps and glaciers accounted for about one-fifth of the increase. But as global ice melting speeds up in coming decades, the sea level rise is predicted to grow significantly.

Some climate models predict global sea level to rise by .9 meters (3 feet during) this century. And if the massive ice sheet covering Greenland, the huge country in the north Atlantic, were to melt completely, the sea level worldwide would increase by a staggering 7 meters (23 feet). Scientists emphasize that such a development is not not likely the coming century or two, but it's one scenario looming in the distant future.

But some signs of change already are visible in low-lying coastal environments around the globe, even locations distant from the Earth's poles. In coastal areas such as southern Florida, Louisiana, and North Carolina, symptoms of rising sea level already appear: severe coastal erosion, elevated groundwater tables, and increased flooding.


Looking to the Future  

One solution to the problem may be reversing global warming by reducing the amount of "greenhouse gases" entering Earth's atmosphere. These gases consist mainly of carbon dioxide produced from the burning of fossil fuels such as coal, oil, and gas. Many scientists believe that greenhouse gases trap the Sun's heat and prevent it from escaping into space, much the way a greenhouse for plants keeps heat inside.

In 1997, 39 industrial nations signed the Kyoto Protocol. The agreement calls for a 5.2% reduction in greenhouse gas emissions below 1990 levels by the year 2112. But there's a catch. The agreement won't kick in until it's ratified by 55% of the countries emitting at least 55% of the gases. A global environmental summit meeting will be held in the Netherlands in November.

Not everyone agrees that greenhouse gases are to blame for rising global temperatures. Some scientists point out that Earth's temperature has warmed for more than 300 years, before coal and oil were burned as fuels. Instead, they suggest the planet may be in the middle of a long-term climate shift that would be happening with or without the rise of greenhouse gases. Some even say that the warming trend could eventually reverse itself.

With more time and research, the debate will ultimately be settled. Until then, scientists will keep gathering data—and listening for the sound of ice cracking.


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