THE GREENHOUSE EFFECT
The Greenhouse Effect



a cartoon Two things are incontrovertible. Over the past century the world has been getting warmer; the past decade has been much the warmest since records began. And scientists predict that it will continue to heat up.


BY FRED PEARCE, ENVIRONMENT CORRESPONDENT, NEW SCIENTIST

Two things are uncertain. First, it is not yet clear what has caused global warming so far. Has it occurred because human activities have added to the "greenhouse gases" in the atmosphere? Or has it resulted from natural temperature fluctuations? Second, nobody knows precisely how much the world will warm for a given amount of added greenhouse gases. Much hinges on socalled "feedbacks" how the planet itself responds to being warmed up.

The greenhouse effect is no myth. It is a natural feature of the atmosphere. Certain gases, such as water vapour, carbon dioxide (CO2), and methane, are called "greenhouse gases" because they trap solar heat in the lower atmosphere. Without them, Earth would be frozen.

But humans are adding to these gases, producing pollutants that cause a gas buildup in the atmosphere. Most important of these human contributions is CO2, which is given off whenever we burn carboncontaining materials, such as coal, oil, or wood. CO2 remains in the atmosphere on average for more than a century. Over the past 200 years, its concentration in the air has risen by a third, largely because growing populations have burnt more trees and failed to replace them and because they have begun to burn massive quantities of fossil fuels.

If we carry on as we are, there will be twice as much CO2 in the atmosphere by late next century. And the heating power of the sun at the earth's surface will rise by about 4 watts per square metre to 240 watts. Not a lot, you might think. But it will raise temperatures directly by an average 1°C.

What is uncertain is how much the changes in the planet caused by warming will themselves amplify that warming. Most solar heat reaching polar regions is reflected from the white ice right back into space. If we melt some of the ice caps, less heat will be reflected. Likely result: a warmer Earth. Global warming will also evaporate more water from the oceans into the air. Water vapour is the most important greenhouse gas of all. So again, extra warming is likely.


The Climate Convention

Developing Countries

Looking For Loopholes



POLAR WARNINGS


Scientists have warned for some time that the polar regions may be the first to show signs of global warming just as they were for the thinning ozone layer. Some of the most persuasive evidence that warming is already occurring here comes from the British research bases in Antarctica that first spotted the Antarctic ozone hole a decade ago.

In mid 1994, the British Antarctic Survey (BAS) reported that, over the past 40 years, average temperatures in the peninsular region of West Antarctica had risen by.5°C 10 times the global average. BAS scientists believe the drastic warming may be a consequence of the breakup of ice sheets in the region, a classic example of the positive feedbacks to global warming predicted by climate modelers. The Wardie ice shelf near the peninsula has shrunk by more than 1,000km2 in the past 25 years.

The warming is most intense in West Antarctica. Here, researchers warn, the ice sheet is precariously perched on top of submerged islands and could suddenly disintegrate. The disappearance of the West Antarctic ice sheet would raise sea levels worldwide by an estimated 6m.




Published by WWF - World Wide Fund For Nature (known in the USA and Canada as World Wildlife Fund), CH 1196 Gland, Switzerland. Any reproduction in full or in part of this publication must mention the title and credit the above mentioned publisher as the copyright owner.

Copyright 1996, The World Wide Fund For Nature