The system of the atmosphere and the earth's surface is like a huge "glass greenhouse", which keeps the earth's surface at a certain temperature all the time and creates an environment suitable for human beings and other living things. In this system, the atmosphere can not only let the solar radiation penetrate to the ground, but also prevent the ground radiation loss. We call this protective effect of the atmosphere on the ground the greenhouse effect of the atmosphere. The gas that causes the greenhouse effect is called "greenhouse gas", which allows the short-wave radiation of the sun to pass freely and absorbs the long-wave radiation emitted by the surface. These gases include carbon dioxide, methane, chlorofluorocarbons, ozone, nitrogen oxides and water vapor, of which carbon dioxide is the most important. In the past century, the global climate has gradually warmed, and the content of greenhouse gases in the atmosphere has also increased sharply. Many scientists believe that the massive emission of greenhouse gases leads to the intensification of the greenhouse effect, which may be the root cause of global warming.
Human activities that emit greenhouse gases include: all fossil energy combustion activities emit carbon dioxide. Among fossil energy sources, coal has the highest carbon content, followed by oil and natural gas. Gas and natural gas leak during the exploitation of fossil energy, releasing carbon dioxide and methane; Industrial production processes such as cement, lime and chemical industry emit carbon dioxide; Methane is emitted by ruminants such as rice fields, cattle and sheep during digestion; Land use change reduces the absorption of carbon dioxide; Garbage releases methane and nitrous oxide.
Humans burn coal, oil, natural gas and trees, and a large amount of carbon dioxide and methane enter the atmosphere, which warms the earth, makes the carbon cycle unbalanced and changes the energy conversion form of the earth's biosphere. Since the industrial revolution, the content of carbon dioxide in the atmosphere has increased by 25%, far exceeding all the historical records of the past 654.38+600,000 years that scientists may have investigated, and there is no sign of slowing down at present.
The main reason for global warming is that human beings have used a lot of fossil fuels (such as coal and oil) and released a lot of greenhouse gases such as carbon dioxide in the past century. These greenhouse gases have high permeability to short-wave radiation from the sun and high absorption to long-wave radiation reflected from the earth, which is often called "greenhouse effect" and leads to global warming.
Forests in the world are mainly divided into three categories: frigid (northern) forests, temperate forests and tropical forests. According to experts, today's forest ecosystem is gradually formed after 8000 years of evolution of nature.
Nowadays, all virgin forests have become the targets of large-scale development and utilization of logging industry. In the tropics, many forests that have disappeared now have been cut down in the past 50 years. From 1960 to 1990 alone, more than 450 million hectares of tropical forests were swallowed, accounting for 20% of the total tropical forest area in the world; Millions of hectares of tropical forests have been degraded by logging, farmland reclamation and mineral exploitation.
In addition, illegal logging and illegal trade in wood products continue to intensify all over the world, especially in developing countries with tropical forests and countries with poor government enforcement, such as Russia. This situation is further aggravated by the demand for cheap wood products in the international market.
According to the climate model, the Intergovernmental Panel on Climate Change predicts that by 2 100, the global temperature will rise by about 1.4-5.8 degrees Celsius (2.5- 10.4 degrees Fahrenheit). According to this forecast, in the past 65,438+00,000 years, the global temperature will change dramatically, which will have a potentially significant impact on the global environment.
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There are about 40 small island developing countries and territories in the world. They face many unfavorable conditions, including lack of resources, economic isolation, degradation of land and marine environment and sea level rise that may be caused by climate change. At the request of the Earth Summit, the United Nations held the "Global Conference on the Sustainable Development of Small Island Developing States" in Barbados in 1994. The meeting emphasized the economic and ecological vulnerabilities faced by small island developing States and adopted an agenda (namely, the Barbados Agenda for the Sustainable Development of Small Island Developing States). The agenda puts forward various policies, actions and measures that governments and the international community need to take to support the sustainable development of these small island developing States.
Zhang Piyuan, a researcher at the Institute of Geographical Sciences and Resources, Chinese Academy of Sciences: "Global warming" has caused changes in the entire ecological environment. First of all, "global warming" leads to sea level rise and rainfall redistribution, which changes the current world climate pattern; Secondly, "global warming" destroys and affects the biological chain and food chain, bringing more serious natural consequences. For example, there is a migratory bird that flies from Australia to northeast China for the summer every year. Due to global warming, the temperature in the northeast of China is rising and the summer is prolonged, so the time for this bird to leave and return to the northeast is delayed accordingly. As a result, a pest eaten by this migratory bird flooded and destroyed a large area of forest. In addition, extreme events related to the environment have increased, such as drought and flood.
Political restrictions on carbon dioxide emissions are equivalent to restrictions on energy consumption, which will certainly have a restrictive impact on all countries in the world. Whether developing countries reduce emissions or developed countries reduce emissions has become the focus of discussion. Developing countries, like a growing child, need to consume energy to promote growth. The greenhouse gas emissions in developing countries are increasing, and the problem of "emission reduction" after 20 13 will inevitably focus on developing countries. The scientific problem of preventing global warming will inevitably lead to the problem of "North-South relations", and the climate problem has actually become an international political issue.
The distribution of climate and precipitation has also changed. Precipitation in the mainland, especially in the middle and high latitudes, has increased, while precipitation in some areas such as Africa has decreased. In some areas, the frequency and intensity of extreme weather and climate events (El Nino, drought, flood, thunderstorm, hail, storm, high temperature weather and sandstorm, etc.). ) have increased.
Ocean: With the rise of global temperature, the amount of water vapor evaporated in the ocean has greatly increased, which has aggravated the warming phenomenon. The reduction of the total heat capacity of the ocean can restrain global warming. In addition, because the ocean releases excessive CO2 into the atmosphere, the real culprit is the plankton community in the ocean.
The impact of global warming on crop growth has both advantages and disadvantages. First, global temperature changes directly affect the global water cycle, causing droughts or floods in some areas, resulting in reduced crop production. Excessive temperature is not conducive to seed growth. Second, the increase of rainfall will actively promote crop growth, especially in drought-prone areas. The increase of CO2 content with global warming will also promote crop photosynthesis and increase yield.
Global warming clouds will increase the water content of clouds and absorb more infrared radiation. However, scientists have also observed that tropical storm clouds will rise to high altitudes at higher temperatures, producing a lot of rainfall, reducing the humidity in the troposphere and slowing down the warming trend.
Generally speaking, the rising of sea ice temperature will accelerate the melting of ice and snow, increase the absorption of solar energy by seawater and aggravate global warming, but at the same time, the melting of sea ice will strengthen the heat flow between air and sea and reduce the temperature.
Human Health (1) Global warming directly leads to excessive temperatures in some areas in summer, because heart disease and various respiratory diseases kill many people every year, among which newborns and the elderly are the most dangerous. (2) Global warming leads to the increase of ozone concentration. Ozone in the lower air is a very dangerous pollutant, which can destroy lung tissue and lead to asthma or other lung diseases. (3) Global warming leads to the spread of some infectious diseases. When a mosquito bites a person with an infectious virus, the virus will follow the blood into the mosquito to start reproduction, and then enter a healthy person through the next bite to complete the spread of the virus. In a certain temperature range, with the increase of temperature, the reproduction rate and bite rate of mosquitoes are greatly improved, and the reproduction and maturity rate of viruses in their bodies will also increase. The rising temperature at night and in winter greatly prolongs the life span and active area of mosquitoes, and increases the incidence of malignant infectious diseases such as malaria, scarlet fever, jaundice and encephalitis. (4) Global warming will cause different natural disasters in different regions, which will directly lead to the reduction of grain production, threaten the hunger and malnutrition of local residents, and accelerate the spread of some water-borne viruses, such as encephalitis, dysentery and high fever.
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