All the energy of climate system basically comes from the sun, so the change of solar radiation is considered as the external cause of climate system change. In the late 1970s, the application of satellite observation made it possible for human beings to accurately measure the changes of solar radiation output outside the atmosphere, and only then did they know that the solar radiation amount was not completely constant, especially during the abnormal activity of sunspots. Many scientists believe that when there are more sunspots, the earth will get warmer, and when there are fewer sunspots, the earth will get colder. However, the mechanism of solar radiation changes affecting climate is still unclear, and there is no strict theoretical or observational support. However, through research, scientists still find that the change of solar radiation and the change of the earth's orbit are not the main causes of modern global warming, which basically excludes the possibility that another natural factor affecting climate change-volcanic eruption is the main cause of global warming in the past century.
Scientists believe that in the natural changes of the climate system, the most important aspect is the change or pulsation of the atmospheric and ocean circulation. This circulation change is the main reason for the change of climate elements at regional scale. Changes in atmospheric and ocean circulation can sometimes be accompanied by changes in landing surface. On the interannual time scale, El Nino, Southern Oscillation (ENSO) and NAO are important examples of atmospheric and ocean circulation changes, and their changes affect weather and climate changes in a large range, even hemispheric or global, and are the basis and basis for making seasonal and interannual climate forecasts at present. For a long time, many meteorologists in the world have devoted themselves to this research, aiming at improving the global and regional climate prediction level. For a longer ten-year time scale, the Pacific interdecadal oscillation (PDO) and related interdecadal Pacific oscillation (IPO) can explain about half of the average change of global surface temperature, which is obviously related to regional temperature and precipitation changes.
With regard to the impact of human activities on climate change, more and more studies show that in the past century, human activities have intensified the process of climate system change. The latest authoritative report-the summary of Working Group I of the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC) points out that the correlation between human activities and climate change has reached 90% in the past 50 years.
The study of climate change caused by the increase of greenhouse gas concentration in the atmosphere by human activities can be traced back to the end of 19 at the earliest. From 65438 to 0896, Svante algie, a Swedish scientist, studied this problem one after another. 1957, Rivera and others published a paper in the United States on the possible climate change caused by the increase of greenhouse gas concentration in the atmosphere. In the same year, the Hawaii Observatory began to observe the concentration of carbon dioxide, which officially opened the prelude to human research on climate change.
What are the human activities that emit greenhouse gases? What greenhouse gases will be produced? How do these greenhouse gases affect climate change?
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.
There are six kinds of greenhouse gases produced by the above-mentioned human activities: in addition to carbon dioxide, greenhouse gases emitted by human activities include methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. The biggest influence on climate change is carbon dioxide, which has a long life. Once discharged into the atmosphere, it can live for up to 200 years, so it is the most concerned.
These greenhouse gases mainly affect climate change through the greenhouse effect. What is the greenhouse effect? Gases such as carbon dioxide in the atmosphere can penetrate the short-wave radiation of the sun (meaning less absorption), warming the earth's surface; However, it prevents the earth's surface from emitting long-wave radiation into space, thus warming the atmosphere. Because this effect of gases such as carbon dioxide is similar to the "greenhouse effect", it is called the "greenhouse effect".
Before the industrial revolution, the "greenhouse effect" caused by gases such as carbon dioxide in the atmosphere made the average temperature of the earth's surface rise from-18℃ to 15℃ that today's natural ecosystems and human beings have adapted to. Once the concentration of greenhouse gases in the atmosphere continues to increase, it further blocks the long-wave radiation emitted by the earth into space. In order to maintain radiation balance, the ground temperature will increase to increase the amount of long-wave radiation. When the ground temperature rises, water vapor will increase (increasing the absorption of long-wave radiation on the ground by the atmosphere), and ice and snow will melt (reducing the reflection of short-wave radiation on the ground), which will further warm the ground, that is, form positive feedback and make global warming more significant. Reasons for Climate Change china.com.cn Time: 2007- 12-06 Comments >> Climate change refers to the climate change directly or indirectly caused by human activities that change the global atmospheric composition. After a long period of observation, this change belongs to natural climate change. Overview of the United Nations Framework Convention on Climate Change: Greenhouse gases in the atmosphere, like natural protective blankets, have a thermal insulation effect on the earth. It makes the earth have a livable temperature-that is, the current comfortable 15℃. Man-made greenhouse gas emissions make this protective blanket thicker, and heat is trapped inside, leading to global warming. Fossil fuel is one of the biggest sources of man-made greenhouse gases. The average temperature of the earth seems to have been very stable in the past 1000 years, and the fluctuation is less than 1℃, which enables human civilization to flourish at the current comfortable temperature of 15℃. But the success of human civilization itself poses a devastating threat to the climate that has taken care of us so far. The natural greenhouse gas "protective blanket" in the troposphere (less than 1% in the whole atmosphere) plays an important role in regulating the earth's climate. When solar energy reaches the earth in the form of visible light, it will warm the surface. The earth, which is much colder than the sun, reflects this energy back into space in the form of infrared radiation or thermal radiation. Greenhouse gases can prevent infrared radiation from entering space directly. The resulting "natural greenhouse effect" makes the earth's temperature 30℃ higher than that without this effect, which is very important for the living conditions of life as we know it. The problem we are facing now is that since the industrial revolution began 250 years ago, our greenhouse gas emissions have been making this protective blanket thicker and thicker at an unprecedented speed. This has brought the most dramatic changes to the composition of the atmosphere in at least 650 thousand years. Unless we make great efforts to reduce greenhouse gas emissions, the global climate will continue to warm rapidly in the next few decades or even longer. Enhancement of greenhouse effect In the long run, "man-made" emissions have become a big problem, because the earth must release energy at the speed of receiving energy from the sun. Because the thick layer of greenhouse gases helps to reduce the energy loss into space, the climate system must make some adjustments to restore the balance between inward and outward energy. The result is the so-called "enhanced greenhouse effect". The climate mainly adjusts the thick greenhouse gas protective blanket through a "global warming" process on the earth's surface and the lower atmosphere. Temperature rise is accompanied by other changes, such as changes in cloud cover and wind pattern. Some of these changes will further strengthen the heating process (positive feedback), while others will hinder this process (negative feedback). These various interactions complicate scientists' efforts to accurately determine the trend of climate change in the coming decades. Greenhouse gas emissions Fossil fuels are formed by long-dead animals and plants, and are the largest source of man-made greenhouse gas emissions. Burning coal, oil and natural gas every year releases a lot of methane and nitrous oxide, releasing billions of tons of carbon, which could have been sealed in the earth's crust. Only deforestation, without afforestation, will also cause a greater amount of carbon dioxide release. At the same time, large-scale livestock raising, rice fields and garbage dumps also emit methane. Nitrous oxide will be produced by using chemical fertilizer. Gases with long service life and used for air conditioning refrigeration, such as chlorofluorocarbons, hydrofluorocarbons and perfluorocarbons, are finally discharged into the atmosphere after industrial treatment. Many of these greenhouse gas emission activities are vital to the global economy and have become a basic part of modern life. In fact, the causes of climate change in developed countries are the same as those in developing countries. Developed countries used to be countries with serious pollution, because due to the development of science and technology, the pollution produced by their production gradually decreased; Developing countries are backward in science and technology, so they are seriously polluted countries. The countermeasures are as follows: First, the energy consumption per unit of GDP has made new progress year by year, with a decrease of 1.79%, 4.04% and 4.59% respectively in 2006-2008. It is estimated that the energy consumption per unit of GDP will decrease by about 20% in 200510. Second, in 2006-2008, small thermal power units were shut down by 342 1 10,000 kilowatts, and backward ironmaking capacity of 60.59 million tons, steelmaking capacity of 43.47 million tons and cement capacity of10.40 million tons were eliminated, which significantly reduced pollution. Third, from 2000 to 2008, the installed capacity of wind power increased from 340,000 kilowatts to100000 kilowatts, the installed capacity of hydropower increased from 79.35 million kilowatts to1630,000 kilowatts, and the installed capacity of nuclear power increased from 2 10/0000 kilowatts to 9 10/00000 kilowatts. China has also made efforts to reduce greenhouse gas emissions in agriculture and rural areas. By the end of 2007, domestic biogas reached more than 26.5 million, equivalent to reducing carbon dioxide emissions by 44 million tons. The fourth is to promote afforestation and enhance carbon sink capacity. The forest coverage rate has increased from 12% in the early 1980s to 18.438+0% at present.