This unprecedented assault on the planet's life-support system could have horrendous long term effects on human health, animal life, the plants that support the food chain -- every strand that makes up the delicate web of nature. Any effort to prevent the damage may prove to be futile but the best the world can hope for is to stabilize the ozone loss.

Soon after the ozone hole over Antarctica was confirmed in 1985, many of the world's governments reached a rapid consensus that action had to be taken. In 1987 they crafted the landmark Montreal Protocol, which called for a 50 percent reduction in CFC production by 1999. Three years later as signs of ozone loss mounted, international delegates met again and called for a total phase out of CFCs by the year 2000. But the schedule was not adhered to by the affluent industrial nations and now the grim news spurred new public warnings and call for faster action.

The vital gas ozone being destroyed is a form of oxygen in which the molecules have three atoms instead of the normal two. That simple structure enables ozone to absorb UV radiation -- a process that is crucial to human health. UV rays can make the lens of the eye cloud up with cataracts, which bring on blindness if untreated. The radiations can cause mutations in DNA, leading to skin cancers. Excess UV radiation may also affect the body's general ability to fight off disease.

Just as worrisome is the threat to the world's food supply. High doses of UV radiation can reduce the yield of basic crops. UV- B, the most dangerous variety of ultraviolet, penetrates scores of metres below the surface of the oceans. There the radiation can kill phytoplankton (one celled plants) and krill (tiny shrimplike animals), which are at the bottom of the ocean food chain. Since these organisms, found in greatest concentrations in Antarctic waters, nourish larger fish, the ultimate consumers -- humans -- may face a maritime food shortage. Scientists believe the lower plants and animals can adapt to rising UV levels by developing UV- absorbing cell pigments. But that works only up to a certain point, and no one knows what that point is.

Alarming reports are coming from many parts of the world. In Australia, scientists believe that crops of wheat, sorghum and peas have been affected and health officials report a threefold rise in skin cancers. Scientists are also concerned about the potential effect of ozone depletion on the earth's climate systems. When stratospheric ozone intercepts UV light, heat is generated. That heat helps create stratospheric winds, the driving force behind weather patterns. Weather patterns have already begun to change over Antarctica. Each sunless winter, steady winds blow in a circular pattern over the ocean that surrounds the continent, trapping a huge air mass inside for months at a time. As the sun rises in the spring, this mass, known as polar vortex, warms and breaks up. But the lack of ozone causes the stratosphere to warm more slowly and the vortex takes longer to dissipate. This leads to even more ozone destruction. The polar vortex acts as a pressure cooker to intensify chlorine's assault on ozone depletion.

As early as in 1974, scientists Rowland and his colleague Mario Molina predicted that CFCs would not disintegrate quickly in the lower regions of the atmosphere. Instead the hardy chemicals would rise into the stratosphere before dissociating to form chlorine monoxide and other compounds. The highly reactive chlorine would then capture and break apart ozone molecules. Each atom of chlorine, it was later determined, could destroy up to 100,000 molecules of ozone -- at a far faster rate than the gas is replenished naturally. With worldwide ozone levels declining somewhat, there was an enormous deficit in Antarctica every year. Determined to understand whether CFCs were the culprit, NASA mounted a series of flights over Antarctica that revealed unusually high concentrations -- up to 1 part per billion -- of chlorine monoxide. They had the smoking gun Rowland and Molina had predicted.

According to Rowland and others it was a combination of factors that made the ozone over Antarctica particularly vulnerable. First, the polar vortex collects CFCs that waft in from the industrialised world. Second, the superfrigid air of the Antarctic night causes clouds of tiny ice crystals to form high up in the stratosphere. When the CFCs break down, the resulting chemicals cling to the crystals, where they can decompose further into chlorine monoxide among other substances. And finally when the sun rises after the long winter night, its light triggers a wholesale demolition of ozone by chlorine monoxide. .

What is alarming, as scientists say is the fact that CFCs remain in the atmosphere for decades after they are emitted. Rowland and Molina estimated that CFCs can last 100 years or more. Even if CFC production stopped today, researchers believe that stratospheric levels of chlorine would continue to rise, peaking during the first decade of this millennium century and not returning to anything like natural levels for at least a century. And that is actually happening these days. By now, scientists believe as many as 40 million metric tons of these potent chemicals have been pumped into the atmosphere.

The consequence is horrendous global warming exposing humans around the globe to catastrophic situations. Heaving seas, scorching summers, dying forests and watery end to the coastal towns and villages are some of the penalties people around the globe have to pay, scientists now believe, for failing to do something about global warming. However Kyoto Climate Change Conference held in December,1997 in Japan reached a consensus that the key culprit to this trend is carbon dioxide. The Kyoto summit set national and regional limits to the release of carbon dioxide, the chief suspect in any global warming, but little was adhered to because of the intransigence of the US, the wealthiest nation having a big role in warming the planet Earth.

This much is virtually certain: gases such as water vapour and carbon dioxide trap infrared radiation warming the world. Water vapour accounts for some 98 per cent of the warming without which the Earth would be 61 degrees Fahrenheit colder. Carbon dioxide accounts for most of the other 2 per cent and the vast majority of that comes from burning fossil fuels (coal, oil, and natural gas). But fiddling with that 2 per cent is like pushing on a long lever: a tiny push can bring huge changes. And the frightening consequences we now see in our part of the world is the rise of global temperatures with several manifestations.

Global temperatures are like bank rates. A small change can make a big difference. A one per cent rise in surface temperature could cause major disruptions in weather patterns that could produce flash floods and unexpected droughts. It could melt the ice shelves in the Antarctica, Arctic and the Himalayas. Much of the warming as experts like Professor Rajendra Pachauri, now head of the UN's Intergovernmental Panel on Climate Change ( IPCC ), says is caused by a doubling of carbon dioxide levels in the atmosphere, which in turn is the result of excessive consumption of fossil fuels. Such layers of gas act like a globe of glass around the planet and reflect back radiated heat from the sun, raising the earth's temperature to debilitating levels.

A rise in temperature like this is expected to cause major disruptions in weather patterns. Ominously, one tenth of the world's known species of high altitude plants and animals that are found in the Himalayas will be under threat. Apart from wreaking havoc on life and property, global warming is likely to have major impact on foodgrain production. Rice and wheat production is expected to fall by 15 per cent over the next decade because of unfavourable climatic conditions.

Global warming would also melt giant ice shelves in the Arctic and Antarctica as already mentioned, pushing sea levels up by over a metre or two. That would swallow up the coastline of many countries like Maldives, New York, Miami in the US and Bangladesh in our region. The rising sea is expected to increase salinity all across India and Bangladesh's coastline causing a Kutch-like barrenness. As if to remind that global warming is for real, two massive shelves in the Antarctica collapsed in the recent past and formed giant floating icebergs in the Indian Ocean.

The concentration of carbon dioxide in the atmosphere has risen from about 280 parts per million (ppm) before the industrial revolution to about 560 in this century. The world has already warmed more than 1 degree Fahrenheit over the last century. Because sea water expands when heated, oceans have risen about a feet. Moreover the IPCC confirmed through their research findings that there was strong evidence to prove that global surface temperature would go up by 1.4 to 5.8 degrees Celsius in this century. Scientists wonder if this could reflect natural climate swings. Over the past 10,000 years, though, century-to-century variability has seldom been this high.

The most powerful argument for trying to mitigate climate change now is based on chemistry : carbon dioxide stays in the atmosphere for a century, on average. As a result, the world would warm even if we stopped burning coal, oil and natural gas today. But if we wait to act until the greenhouse gas is upon us, it will take decades to turn it around. Even stabilising emissions doesn't stabilise climate: as long as the gases keep rising, even at current rates.

Despite the advance warning of the consequences of global warming, most countries exhibit a strange reluctance to combat the phenomenon. Even after the failure of the efforts made under UN framework that adopted policies and measures aimed at reducing greenhouse gas emissions to 1990 levels, another effort was made under the banner of Kyoto Protocol in 1997 that worked out precise commitments for various nations to meet by 2012. But with the U.S. backing out of the protocol on the ground that its implementation would seriously affect its economy, it ended up as a non-starter. If the international efforts do not get off the ground immediately, the world especially poorer countries like Bangladesh, Maldives and even India seem doomed to plenty more misery and disasters than what is being experienced now.

Md Asadullah Khan is a former teacher of physics and controller of examinations, BUET.