ioxide in the atmosphere has been increasing by 0. 4 per cent a year because of the use of fossil fuels such as oil, gas, and coal. The cutting of tropical forests has also been a contributing factor in the carbon cycle. Other gases that contribute to the greenhouse effect, such as methane and halocarbons, are increasing even faster. The net ef - fect of these increases could be a worldwide rise in temperature, estimated at 2 to 6 G (4 to 11 F) over the next 100 years. Warming of this magni - tude would alter climates throughout the world, affect crop production, and cause sea levels to rise significantly. If this happened, millions of peo - ple would be badly affected by flooding.
GLOBAL WARMING
Global warming is an increase in the earths temperature due to the use of fossil fuels and other industrial processes leading to a build-up of "greenhouse gases" (carbon dioxide, methane, nitrous oxide) in the at - mosphere. It has been known since 1896 that carbon dioxide helps stop the suns infrared radiation from escaping into space and thus functions to maintain the Earths relatively warm temperature (this is called the green - house effect). The question is whether the increasing levels of carbon di - oxide in the atmosphere will lead to elevated global temperatures, which could result major climatic changes, and have serious problems for agri - cultural productivity.
Since 1850 there has been a mean rise in global temperature of ap - proximately 1 С (1. 8 F), but this rise could just be part of a natural fluctu - ation. Such fluctuations have been recorded for tens of thousands of years.
The potential consequences of global warming are so great that many of the worlds top scientists have urged immediate action, and have called for interna
Страницы: << < 9 | 10 | 11 | 12 | 13 > >>