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Some gases in the atmosphere allow visible light to pass through but they block much of the heat which is reflected from Earth's surface– in the same way as the glass windows in a greenhouse. Without this greenhouse effect, temperatures in the world would be lower by 35 degrees Celsius, most of the oceans would freeze, and life would cease or be totally changed. According to the theory of global warming, an increase in greenhouse gases in the atmosphere will produce too high temperature increases.

Aside from water vapour, the main greenhouse gases are carbon dioxide, methane, nitrous oxide. Of these, carbon dioxide is the most important.

The most dramatic consequence of the warming would be a rise in sea level from the melting of polar ice and glaciers, a rise that the Environmental Protection Agency projects to be 20 feet in the year 2300. Arid then large parts of territories along sea and ocean coasts will be under water.

Scientists don't think that mankind alone is responsible for the melting of glaciers and the rise of sea levels up to 25 centimetres this century. But we have created conditions that accelerate the process.

A majority of climatologists feel that a risk of global warming exists, although there is much disagreement about the extent and timing. At the 1992 United Nations Conference on Environment and Development, more than 150 countries signed the Convention on Climate Change for the control of emissions of greenhouse gases.

In the early 1990s, the United States produced 23 per cent of global emission, Western Europe 14 per cent, Japan 5 per cent and China 12 per cent. Although emissions have grown much during the past 40 years, they began levelling off in the late 1980s and early 1990s.

In December 1997 about 160 nations took part in the conference in Japan which was to limit emission of carbon dioxide and other greenhouse gases in the future.


Date: 2015-12-17; view: 1974

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