Global warming potential

Global warming potential

At present, the concentration of CO2 in the atmosphere is increasing at an annual rate of 0.4% to 0.5%. According to meteorological data and scientists’ speculations, the concentration of CO2 in the atmosphere remained basically around 275×10-6 from 10,000 years ago to the early stages of the Industrial Revolution. After the Industrial Revolution, the concentration of CO2 increased sharply, 280×10-6 in 1750, 300×10-6 in 1900, 315×10-6 in 1958, 340×10-6 in 1980, and 354×10-6 in 1989 , it was 360×10-6 in 1998 and reached 380×10-6 at the end of the 20th century, which is very close to the acceptable upper limit of 390×10-6.

Although there is still a lack of effective quantitative models to describe the direct relationship between CO2 emissions and global warming, if you carefully compare and analyze the temperature of the earth 4000~8000 years ago and the ecological environment at that time and the current earth temperature and ecology The environment, then, the decisive impact of temperature changes on the global ecosystem is by no means sensational.

Some climatologists predict that the global average surface temperature will rise by 1°C by 2025, and will rise by 1.5 to 4.5°C by the middle of the 21st century. The World Meteorological Organization has calculated that by 2030, the earth’s average temperature may increase by 4.5°C.

Global warming will cause the seawater to expand slightly, and the ice on the earth will melt and flow into the ocean, which will increase the volume of the seawater. The global sea level is indeed slowly rising, and the rate of increase is 1~2mm per year. In the past 100 years, the world’s sea level has risen by 10~15cm. For the benefit of future generations, people must pay attention to the cumulative effect of this slow rise. The sea may flood many coastal areas, many islands will disappear, and natural disasters such as dry weather, floods, and storms will occur more frequently.

CH4 etc. are also important sources of greenhouse gases. Coal often coexists with methane gas, so when coal is mined, methane gas is always released. Every 1t of coal mined will release an average of 13kg of CH4. The greenhouse effect of CH4 gas on climate is 23 times that of CO2.

Recent studies believe that in addition to the main contribution of increasing the concentration of CO2 in the enhancement of atmospheric greenhouse effect caused by human activities, atmospheric particulate matter such as carbon black also has the effect of greenhouse effect, which is an important cause of global climate change. Character.

In recent years, international survey studies conducted over the Indian Ocean show that the indirect effect of carbon black particles on the greenhouse effect is that it can absorb part of the solar radiation, thereby reducing cloud cover and causing the warming and evaporation of water droplets in the cloud. That is, the atmosphere is warmed by the change of clouds.

Certain gases in the atmosphere (CO2, CH4, N2O, etc.) can enhance the greenhouse effect of the atmosphere because they can absorb part of the infrared radiation emitted by the earth into space. The intensity of this absorption and the wavelength involved depend on the nature and concentration of the gas and other greenhouse gases that are present at the same time. In order to evaluate the relative ability of various greenhouse gases to affect the greenhouse effect, a parameter called “Global Warming Potential” (GWP) has been proposed. This is a very useful parameter, with which people can compare the climatic effects of various gases. The method of evaluation is to calculate the global warming potential of a certain amount of a certain gas within an agreed period. Generally, such periods are 20 years, 100 years, and 500 years. This comparison value will change as the period increases. The time limit of 100 years is taken below to illustrate this definition.

GWP is based on CO2 gas as an evaluation reference, that is, GWP(CO2)=1. For CH4, GWP(CH4)=23, which means that if 1kg of CH4 is emitted into the atmosphere, it will end in the next 100 years. , It will have the same impact on the climate as 23kg of CO2. Therefore, CH4 is a gas with a stronger climate warming effect. In the same way, the GWP value of N2O is 296, and the GWP value of CFCs is 5700~11900. The most harmful gas that has the greatest effect on the greenhouse effect is SF6, which has a GWP value of 22,200. If you compare the GWP value in different periods (20 years, 100 years, and 500 years), you will find CH, The GWP value corresponds to 62, 23 and 7 or CH in 20 years, 100 years and 500 years, respectively, and the GWP values ​​show a decreasing trend. The GWP value of SF (corresponding to 15100, 22200 and 32400 for 20 years, 100 years and 500 years respectively) has shown an increasing trend over time. This is related to the atmospheric lifetime of this greenhouse gas. If the atmospheric lifetime of a certain gas is shorter than that of CO2, its GWP value will increase over time. The ability of a certain gas to be eliminated depends on its chemical activity. The weaker the chemical activity, the longer it will exist in the atmosphere.

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