Combined with the movie The Day After Tomorrow, this paper discusses what global warming is and its causes.

One is man-made reasons, human beings burn a lot of fossil fuels in production and life, releasing a lot of greenhouse gases, and then destroying the ecological environment.

Second, it is natural reasons. The climate on the earth is cold, warm, dry and wet, and we are now in the rising stage of temperature fluctuation. So the global climate is also warming.

Now it is generally believed that what causes the excessive emission of carbon dioxide in the atmosphere? The emission of automobile exhaust and the extensive use of chemical fuels. A series of environmental and resource problems brought about by population growth. This is what we usually call the "greenhouse effect", and carbon dioxide is also called greenhouse gas. The harm of greenhouse effect is obvious, which will lead to climate warming and further sea level rise. For those low-lying coastal areas, this will mean disaster.

Now climate warming has attracted the attention of the whole world.

In recent decades, greenhouse gases such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide and ozone released by human activities have been increasing, resulting in changes in atmospheric composition. Many scientists assert that if this situation continues, the accumulation of greenhouse gases is likely to trigger global warming. In fact, due to the influence of human beings, local warming has already appeared.

According to statistics and calculations, the carbon emitted into the atmosphere by global combustion has been increasing slowly for six consecutive years, reaching 5.925 billion tons in 1994. At the same time, due to deforestation, the increased carbon in the atmosphere is also between1.1-360 million tons. For a long time, there is a close and obvious correlation between global temperature and the content of carbon dioxide in the atmosphere. Although there is no evidence that the change of carbon dioxide level directly causes the change of temperature, since the middle of18th century, carbon dioxide and other greenhouse gases in water have reached an unprecedented concentration in the past160,000 years.

Although chlorofluorocarbons, methane and nitrogen oxides also accumulate in the atmosphere. But the impact of carbon dioxide on global temperature is at least 60% higher than the sum of these gases. The increase of carbon dioxide concentration is the main cause of global greenhouse effect.

Global carbon emissions are constantly changing with economic growth. In 1860, the number of people living in the world was 93 million tons, which rose sharply to 525 million tons in 1900, and reached16.2 million tons in 1950. But it is still less than 1/3 of Sweden's emissions. Since 1970s, the growth rate of emissions has slowed down, with an average increase of 4.6% from 1950- 1973, while the average increase from 1973- 1988 is only 1.6%. In recent years, carbon emissions have been relatively stable, which is due to the economic recession of western industrialized countries and the economic contraction of the former Soviet bloc. But it will maintain steady growth in the future.

Although the growth of carbon emissions in recent years has mainly occurred in Asian and Latin American countries in the process of industrialization. However, according to the per capita emissions, the developing countries only have 0.5 tons, and the emissions of 100 industrialized countries have reached more than 3 tons. From the total, developing countries only account for 1/3 of the global total, and developed countries account for more than 2/3. It is of concern that the contribution rate of carbon emissions in developing countries is increasing, and the number of chickens doubles every 14 years.

Before the year 2000, global carbon emissions are expected to increase at an annual rate of 65,438+0%-2%. However, even if carbon emissions remain at the current stable level, it still exceeds the absorption capacity of the global oceans and forests, resulting in more and more carbon dioxide trapped in the atmosphere. At the end of 1994, the carbon in the atmosphere exceeded 4 billion tons, and the concentration of carbon dioxide rose from 357/0ppm at the end of last year to 358.9ppm, which was the fastest growth in six years. Since 1980, 350 billion tons of carbon have been added to the atmosphere, of which about150 billion tons are still stuck in the atmosphere.

Scientists estimate that in order to stabilize the total amount of carbon in the atmosphere, global carbon emissions should be reduced by at least 60%. The Framework Convention on Climate Change signed at the global summit in 1992 requires industrialized countries to formulate policies corresponding to the emission reduction targets in the future 10 and take practical steps.

According to the calculation, the average temperature of the lower atmosphere in 1994 is 15.32℃, which is the hottest year since 19 1 year in the Philippines and the hottest five years since 1987. Just like the daily temperature change anywhere, the annual average temperature of the lower atmosphere is changeable and difficult to explain. In the last century, the trend of rising temperature has been obvious. Now the global temperature is 0.3-0.6℃ higher than that in 1880. Starting from 1980, there are 10 hottest years.

The eruption of Mount Pilatupo is the biggest volcanic eruption in this century, which has discharged millions of tons of dust into the upper atmosphere and spread all over the world. These dust blocks the sunlight, which is enough to reduce the temperature of the lower atmosphere by half a degree Celsius. However, these dust particles settled to the earth's surface at a slow speed in the next two years. By the beginning of 1994, the influence of Mount Pilatupu had ended, so the global temperature began to return to the high temperature level before the eruption of Mount Pilatupu.

Now, meteorologists have monitored a series of data from temperature monitoring stations around the world. Most meteorologists believe that with the continuous accumulation of greenhouse gases in the atmosphere, especially carbon dioxide, the trend of global warming will eventually recover. It is unclear when the warming trend will resume. How big is it?

The Intergovernmental Panel on Climate Change (IPCC), funded by some United Nations agencies, pointed out that if the use of fossil fuels continues to increase steadily for a long time, the global average temperature will reach 16- 19℃ by 2050, which is faster than the previous warming and accelerates global warming.

Global warming predicted by the Intergovernmental Panel on Climate Change will have various impacts on the world. Although it is difficult to predict the extent to which every region in the world will be affected by it, higher temperatures will lead to rising sea levels and melting polar ice. The sea level will rise by 6 cm every 10, and some coastal areas will be submerged. Global warming may also change climate changes, including rainfall, soil temperature and seasonal length, which may lead to defects and destruction of many ecosystems and threaten the safety of thousands of biological species. Climate change will have some significant impacts on human beings, which may change the main grain producing areas within several decades.

Second, the depletion and destruction of the ozone layer.

The atmosphere with high ozone concentration is about 10-50 kilometers away from the earth's surface, and the maximum concentration is 25 kilometers, forming an ozone layer with an average thickness of 3 mm. It can absorb solar ultraviolet radiation, provide the earth with a barrier against ultraviolet radiation, and store energy in the upper atmosphere to regulate the climate. The destruction of the ozone layer will make excessive ultraviolet radiation reach the ground, causing health hazards; The change of stratospheric temperature leads to the abnormal climate of the earth, which affects plant growth and ecological balance.

Over the past half century, with the rapid development of industry and agriculture, a large number of nitrogen oxides have been discharged into the atmosphere by human activities, and a large number of nitrogen oxides and other gases have been discharged into the ozone layer by supersonic aircraft flying at a high altitude and constantly launching aerospace vehicles. In addition, people also produce a large number of chlorofluorocarbons (CFCs), such as CFCL3 (Freon-1 1), CF2CL2 (Freon-12), CCI2FCCIF2 (Freon-13), CCIF2 (Freon). According to statistics, during the period of 1973, the global * * * produced about 4.8 million tons of these two fluoride ions, most of which were released into the lower atmosphere and then entered the ozone layer. Freon is very stable in the troposphere. It can stay in the atmosphere for a long time without change, and gradually spread to the ozone layer, where it reacts with ozone to reduce the concentration of the ozone layer. The elimination of ozone is mainly due to the reaction of active chlorine free radicals and chlorine oxygen free radicals produced by the photolysis of nitric oxide and chlorofluorocarbons with odor, which gradually reduces the ozone concentration in the ozone layer.

Since the discovery of a huge "ozone hole" over Antarctica in the late 1970s, people have paid great attention to the problem of ozone consumption. It is estimated that a decrease in ozone concentration in the ozone layer 1% will increase ultraviolet radiation on the ground by 2%, leading to an increase in the incidence of skin cancer by 2%-5% (300,000-400,000 new patients in the United States each year). Recently, the United States and other countries have banned the use of chlorofluorocarbon sprays and strictly controlled the production and use of other chlorofluorocarbons. Recently, it is estimated that ozone will be reduced by 5%-9% if CFC is continuously used at the level of 1977. According to the latest statistics of the United Nations Environment Programme, the trend of ozone reduction is still developing, and the stinking hole over the Antarctic is still expanding, and similar stinking holes have appeared over the Arctic, but the scope is smaller.

At present, an important measure to prevent the ozone layer from being destroyed in the global environmental field is to reduce the output of chemicals that consume stratospheric ozone. According to statistics and estimates, the global CFC production further decreased in 1994, and maintained a downward trend for six consecutive years. The peak value of total output ratio 1988 decreased by 77%.

Thanks to diplomatic efforts, the Montreal Protocol signed in 1987 was further strengthened in 1990 and 1992. Industrialized countries agreed to stop CFC production before 1995 12 3 1, while developing countries that have signed up have a grace period of 10. By the end of 1994, 146 countries in the world had signed the protocol.

Although the production of CFCs in developing countries is much lower than that in industrialized countries, the demand for these chemicals has greatly increased. In the early 1990s, the consumption of CFCs in India, China and some other developing countries was less than half that in the United States, but the consumption of CFCs in some of these countries increased at almost double-digit rates.

In order to help developing countries reduce and eliminate CFCs, industrialized countries should establish funds to develop technologies to replace CFCs. However, the donors to the Fund have not fulfilled their commitments. During the period of 199 1- 1994, the amount donated by donor countries was only 2/3 of its initial commitment of $393 million. Lack of funds and technology is still the main difficulty for developing countries to reduce HCFCs.

Another reason that hinders CFC production reduction is the growing "international CFC black market". 1994, the EU imported about 2,500 tons of CFC from Russia and Estonia, equivalent to 10% of the EU's total legal imports. In the United States, the high license tax on chlorofluorocarbons has further stimulated speculators. 1994 CFCs illegally imported by the United States were estimated to be around 1 10,000 tons, accounting for 10% of the total output of the United States.

It is now clear that the destruction of the ozone layer will enhance the ultraviolet radiation on the earth's surface and increase the harm to living things. Experimental and epidemiological studies show that the increase of ultraviolet-β may have different effects on human beings and organisms, including the increase of skin incidence of non-melanoma and the decrease of crop yield.