Atmospheric carbon dioxide (CO₂) is the raw material for plant photosynthesis to synthesize carbohydrates. Its increase can increase photosynthetic products, which is undoubtedly beneficial to agricultural production. At the same time, it is a gas with a greenhouse effect and has an important impact on the earth's heat balance. Therefore, its increase affects agriculture by affecting climate change. In addition, there are trace gases with greenhouse effect in the atmosphere such as methane, chlorofluorocarbons, carbon monoxide, ozone, etc. The role of carbon dioxide in the total greenhouse effect accounts for about half, and the rest are the effects of the above various trace gases.
The concentration of carbon dioxide tends to increase year by year. In the 1950s, the annual average mass score was about 315×10 (-6), and in the early 1970s, it had increased to 325×10 (-6), which exceeded 345×10 (-6). An annual increase of 1.0-1.2×10 (-6), or an annual growth rate of about 0.3%. Based on most measurement results, the mass fraction of carbon dioxide before the industrial revolution was 275×10 (-6).
The main reason for the increase in the concentration of carbon dioxide in the atmosphere is the large-scale exploitation and use of fossil fuels after industrialization. Since 1860, the average annual growth rate of carbon dioxide emitted by burning mineral fuels has been 4.22%, and the total emissions of various fuels have reached about 5 billion tons per year in the past 30 years.
Another major reason for the increase in carbon dioxide in the atmosphere is the cutting of trees for fuel. Forests were originally a major "reservoir" in the atmospheric carbon cycle. Each square meter of forest can assimilate 1-2 kg of carbon dioxide. Deforestation turns the original "pool" of carbon dioxide into another "source" of carbon dioxide emissions into the atmosphere. According to estimates by the World Food and Agriculture Organization (FAO, 1982), about 2.4 billion cubic meters of wood were harvested every year in the late 1970s, of which about half was burned as fuelwood, and the resulting increase in the mass fraction of carbon dioxide could reach 0.4×10 (- 6) Around.
According to the above comprehensive analysis, if the current increase in the concentration of carbon dioxide and other greenhouse gases is used, by the 2030s, the total effect of the increase in carbon dioxide and other greenhouse gases will be equivalent to the doubling of the carbon dioxide concentration before industrialization, which can cause global temperature rise by 1.5- 4.5°C exceeds the rate of warming that has occurred in human history. As the temperature rises, the ice caps at the poles may shrink, and the melting snow can raise the sea level by 20-140cm, which will have a serious direct impact on coastal cities.