The perils of global warming

Melting iceberg -- rising sea level

The wanton exploitation of the Earth has continued despite the fact that scientists for more than two decades have warned that cars and factories are spewing enough gases into the atmosphere to heat the Earth in a greenhouse effect that could eventually produce disastrous climatic changes.

Carbon dioxide is released in large quantities when wood and such fossil fuels as coal, oil, and natural gas are burned. As society industrialized in the 1800s, coal-burning factories began releasing carbon dioxide faster than plants and oceans could absorb the gas.

In the early 1800s, people began burning oil and gas at a prodigious rate. Increasing population led to widespread cutting of trees in less developed countries These trees are no longer available to soak up excess carbon dioxide and whether they are burned or left to rot, they instead release the gas.

Estimates by scientists convincingly suggest that by the late 1800s, atmospheric carbon dioxide had risen to between 280 and 290 parts per million. In 1989 it stood at 350 ppm and by 2050 it could reach 500 to700 ppm, higher than it has been in millions of years.

But carbon dioxide, once thought to be exclusively responsible for the greenhouse problem, is now known to cause only half the problem. The rest comes from other gases. Chlorofluoro carbons or CFCs are not only destroyers of the stratosphere's ozone layer, but powerful greenhouse gases as well. So are nitrogen oxides, which are pollutants spewed out of automobile exhausts and power plant smokestacks.

Another greenhouse gas is methane, the primary component of natural gas. Methane is also generated by bacteria living in the guts of cattle and termites, the muck of rice paddies, and the rotting garbage in landfills Each of these sources is fostered by human activities -- even the termites, which on the clearings left after the tropical rain forests are cut down. Human contribution to the greenhouse effect comes from so many basic activities that man cannot realistically stop the process, only slow it down.

The world now knows that the danger is shining through the sky. The evidence is now overwhelming that the Earth's stratospheric ozone layer, our shield against the sun's hazardous ultraviolet rays, is being eaten away by man-made chemicals far faster than any scientist had predicted. No longer is the threat just to our future, the threat is here and now.

The 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 and just about every other strand that makes up the delicate web of nature.

In 1992 NASA's orbiting satellite discovered record high concentration of chlorine monoxide (ClO), a chemical by-product of a group of man-made chemicals called chlorofluorocarbons (CFCs), were chief agents of ozone destruction.

Mounting evidence has demonstrated that under certain conditions these compounds set off chemical reactions that rapidly destroy ozone. Humans are altering the Earth's surface and changing the atmosphere at such a rate that we have become a competitor with natural forces that maintain our climate.

Indeed if the ozone layer diminishes over populated areas -- and there is ample evidence that it has begun to do so, although nowhere as dramatically as in the Antarctic -- the consequences could be dire. Ultraviolet radiation, a form of light invisible to the human eye causes sunburn and skin cancer. In addition it has been linked to cataracts and weakening of the immune system.

Potentially more damaging than ozone depletion and far harder to control is the greenhouse effect caused in large part by carbon dioxide. The effect of carbon dioxide in the atmosphere is comparable to the glass of a greenhouse: it lets the warming rays of the sun in, but keeps excess heat from radiating back into space. Indeed, man-made contributions to the greenhouse effect, mainly carbon dioxide that is generated by the burning of fossil fuels, it is now widely believed, may be hastening a global warming trend that could raise average temperature between 2 degrees and 8 degrees by the year 2050

Even if it is a fact that region by region effects of rapid atmospheric warming are far from clear, scientists are still confident of the overall trend. In the next half century they fear dramatically altered weather patterns, major shifts of deserts and fertile regions, intensification of tropical storms, and a rise in sea level, caused mainly by the expansion of sea water as it warms up.

The arena in which such projected climatic warming will be first played out is the atmosphere, the ocean of gases that blankets the Earth. It is a remarkably thin membrane: if the Earth were the size of an orange, the atmosphere would be only as thick as its peel The bottom layer of the peel, the troposphere, is essentially where all global weather takes place; it extends from the Earth's surface to a height of ten miles. Because air warmed by the Earth's surface rises and colder air rushes down to replace it, the troposphere is constantly churning. A permanent air flow streams from the poles to the equator at low altitudes, and from the equator to the poles at higher levels. These swirling air masses distorted by the rotation of the Earth generate prevailing winds that drive weather across the hemispheres. Above this turmoil, the stratosphere extends up to about 30 miles. In the lower stratosphere, however, rising air that has been growing colder at gradually higher altitudes begins to turn warmer The reason can be attributed to ozone.

Ozone is a form of oxygen that rarely occurs naturally in the cool reaches of the troposphere. It is created when ordinary oxygen molecules are bombarded with solar ultraviolet rays, usually in the stratosphere. This radiation shatters the oxygen molecules, and some of the free oxygen atoms recombine with oxygen molecules to form O3 or ozone. This configuration gives it a property that two-atom oxygen does not have: it can efficiently absorb ultraviolet light. In doing so, ozone protects oxygen at lower altitudes from being broken up and keeps most of these harmful rays from penetrating to the Earth's surface.

The first effort to combat the greenhouse effect is to ban the use of CFCs which are used in refrigeration and air conditioning as coolants, as cleaning solvents in factories as blowing agents to create certain kinds of plastic foam, seat cushions, furniture stuffing and carpet padding. Some estimates say that there are about several billions of refrigerators and air conditioners now in use in the world. So ridding the world of the millions of tons of ozone-depleting chemicals is not just a big job, it may be the biggest job the nations of the world have ever taken on.

In the 60 years since Du Pont began marketing the miracle refrigerant it called freon, chlorofluorocarbons have worked their way deep into the machinery of what much of the world thinks of as modern life -- air conditioned homes and offices, climate-controlled shopping malls, refrigerated grocery stores and squeaky-clean computer chips.

Extricating the planet from the chemical burden of that high-tech life style -- for both those who enjoy it and those who aspire to it -- will require not just technical ingenuity but extraordinary diplomatic skill. The goal is to find substances and processes that can replace CFC-based systems without doing further harm to the stratosphere -- an endeavour that is well under way. Except for medical aerosols, some fire-fighting equipment, and certain metal cleaning applications, there are now effective substitutes for every ozone-depleting chemical.

Another strategy is to burn as much methane as possible. This adds carbon dioxide to the air, but getting rid of methane is well worth it. Both gases trap heat, but as a greenhouse gas, methane traps 20 times as much heat as carbon dioxide. Methane from cattle feedlots will be difficult to collect, but the gas in garbage landfills is already being tapped and burned at many sites around the US.

In a certain landfill in New York City's Staten Island, for example, methane that could have escaped into the air is being collected by a gas company and used to heat thousands of homes. The technique involves driving a pipe into the depths of the garbage, and then trapping the gas that rushes out. This could be done at landfills in our country too The next most important step to counteract global warming is to slow, and more precisely, stop deforestation.

That being a daunting task, the most effective strategy should be to plant trees and plenty of them, to absorb carbon dioxide from the air. The planting can be encouraged at all levels of the society, from individuals putting an extra tree or two in the backyards to local communities and private organizations like NGOs and business houses planting an acre at a time and governments reforesting on a more widespread basis.

Unhappily, the country's forest resources are disappearing at an alarming rate. The official figures published in the recent past indicate that Bangladesh at the moment retains only 6 percent of its forest cover. In a survey concluded in the late 2000s, experts have predicted that at present rates, Bangladesh will lose all its forest resources in the next five years. The vast region of unbroken green that surrounds the Sunderbans and Chittagong hill-tracts has been under assault by several groups that include loggers, shrimp cultivators and environmental refugees.

Tree planting will have negligible impact, however, if people continue to pump carbon dioxide into the atmosphere at current rates. Realistically, wood and fossil fuel burning can never be eliminated, but they can be cut down significantly. This goal can be achieved through conservation. It is worth mentioning here that in the United States tax on CFCs helped to encourage the development of non-ozone depleting substitutes. Imposition of tax in Sweden on sulphurous diesel fuel helped the development of new and less polluting fuels. The carbon dioxide tax would be a powerful incentive for consumers to switch from high carbon dioxide fuels, such as coal and oil to power sources that produce less carbon dioxide, notably natural gas

To ward off the increasing catastrophic scenario, the world, and most importantly Bangladesh, must move away from fossil fuels for most of its energy needs. Of all the known non-fossil energy sources, only two have hit world attention. These are solar and nuclear, neither of which generates any greenhouse gases at all. Solar power is especially attractive. It produces no waste and it is inexhaustible. Not all solar power comes directly from the sun: both wind and hydro-electric power are solar, since wind is created by the sun's uneven warming of the atmosphere, and since the water that collects behind the dams was originally rain, which in turn was water vapour evaporated by solar heating.

Since wind and hydro-electric power can be generated at only a few sites, governments in all countries, including Bangladesh, have to increase financing for research to develop efficient, low-cost photovoltaic power. Photovoltaic cells which produce electric current when bathed in sun-light were in vogue during the energy crisis of the 70s.

Some time early in this century, solar enthusiasts hope to see vast tracts of photovoltaic collectors producing cheap electricity that can be transmitted over long distances. At the same time, this electricity could be used to produce hydrogen from water. That could open up vast possibilities. Cars, for example, could be redesigned to run on hydrogen that would produce dramatic reduction in carbon dioxide emission.

Md. Asadullah Khan is a former teacher of physics and Controller of Examinations, BUET.