1. Global climate change. In the past century, the average global surface temperature rose by .3 to .6 degrees Celsius, and the sea level rose by 1 to 25 centimeters. At present, the concentration of carbon dioxide in the earth's atmosphere has increased from 28ppm before the industrial revolution (175) to nearly 36ppm.
2. Ozone layer destruction and depletion. Since the ozone hole appeared over Antarctica in 1985, the phenomenon of ozone layer depletion over the earth has been increasing. By 1994, the ozone layer over Antarctica had destroyed 24 million square kilometers. Now, the ozone layer is thinning over the United States, Canada, Western Europe, the former Soviet Union, China and Japan.
Because ODS is quite stable and can exist for 5-1 years, most of the discharged ODS is still in the atmosphere. As they rise to the stratosphere, they will react with the ozone layer there and decompose ozone molecules. Therefore, even if the world completely stops emitting ODS, it will be another 2 years before mankind can see the signs of ozone layer recovery.
3. Acid rain pollution. Now the word "acid rain" has been used to refer to the transfer of acidic substances from the atmosphere to the ground in the form of wet deposition (rain, snow) or dry deposition (acidic particles). Most of the acid rain is sulfuric acid and nitric acid, which mainly comes from the extensive use of fossil fuels by human beings, and a large amount of sulfur dioxide and nitrogen oxides are discharged into the atmosphere. Europe is a big acid rain area in the world, and so are the United States and eastern Canada.
in northern Europe, due to the high natural acidity of soil, acidification of water and soil is particularly serious, and acidification of some lakes leads to the extinction of fish. According to the national surface water survey data of the United States, acid rain caused 75% of lakes and about half of rivers to be acidified. The Canadian government estimates that 43% of Canada's land (mainly in the east) is highly sensitive to acid rain, and 14, lakes are acidic. Water acidification will change aquatic ecology, while soil acidification will impoverish soil and lead to the degradation of terrestrial ecosystem.
4. Land desertification is the most serious environmental and socio-economic problem in the world today. In 1991, the United Nations Environment Programme assessed the global desertification situation as follows: the global desertification area has reached nearly 3.6 billion hectares, accounting for about a quarter of the global land area, which has affected 1/6 of the world's population (about 9 million people) and more than 1 countries and regions. Moreover, the speed of desertification expansion is that 6 million hectares of land in the world become desert every year, of which 3.2 million hectares are pasture, 2.5 million hectares are dry land, 125, hectares are irrigated land, and another 21 million hectares are degraded and unable to grow grains.
5. Water crisis, many areas in the world are facing serious water crisis. According to international experience, 1 cubic meters of reusable freshwater resources per person per year is a basic indicator, and countries below this indicator may suffer from long-term water shortage that hinders development and harms health. However, at present, about 2 countries in the world have fallen below this index, mainly in West Asia and Africa, with a total population of over 1 million. On the other hand, water pollution caused by domestic wastewater, industrial wastewater, agricultural sewage, solid waste leakage, air pollutants, etc., has greatly reduced the amount of freshwater resources available in the world.
6. Destruction of forest vegetation. Due to the difficulty of speculation, there is no accurate value of forest area in the world. However, it is estimated that the forest area on the earth is about 3-6 billion hectares, accounting for 2%-4% of the land area, of which about half are tropical forests (including tropical rainforests and tropical monsoon forest), and the other half are mainly coniferous forests in the sub-frigid zone. According to the measured dry weight of forest plants, tropical forest is twice as large as coniferous forest in sub-frigid zone, so tropical forest accounts for a large part of the total biomass on land.
7. Biodiversity has dropped sharply. Scientists estimate that there are about 14 million species on the earth, but the rate of biodiversity loss on the earth is faster than at any time in history. For example, the extinction rate of birds and mammals may be 1 to 1, times that of their undisturbed nature.
8. Destruction and pollution of marine resources. It is estimated that 95 million people all over the world regard fish as the main source of protein. However, in recent decades, the over-utilization of marine living resources and the increasingly serious pollution of the ocean by human beings may cause obvious degradation of marine productivity and marine environmental quality on a global scale. In 1993, 77.7% of the 11 million tons of fish caught in the world came from the ocean. At that time, FAO estimated that more than 2/3 of marine fish had been overfished, especially 25% of the fish with data were extinct or endangered due to overfishing, and another 44% of the fish had reached the biological limit.
on the other hand, most of the wastes and pollutants produced by human activities eventually enter the ocean. Every year, billions of tons of sludge, sewage, industrial waste and chemical waste are directly discharged into the ocean, and nearly billions of tons of sludge, wastewater and waste are brought into coastal waters by rivers every year, causing changes in coastal habitats and destroying animal habitats and breeding grounds.