What will happen to the climate in the future?

At present, the earth is in the relatively warm interglacial period of the Quaternary Great Ice Age. There are two diametrically opposed views on the prediction of future climate change in the world. Some scholars think it will be cold in the future, while others think it will be warm. So, what are the observed facts so far?

What changes have taken place in the climate of the world and China?

The observation facts of global and China climate change mainly include the following points:

Temperature change

The observation records and research results show that the average temperature of global land and ocean surfaces has been on the rise since 186 1, and it rose by about 0.6℃ in the 20th century.

Globally, the 1990s was the warmest year since 186 1, and 1998 was the warmest year since 186 1. In recent 100 years, the measurement records of global temperature instruments have also shown obvious interdecadal changes. The most important warming in the 20th century occurred in 19 10~ 1945 and 1976~2000. Based on a large number of proxy data, the study on the climate change in the northern hemisphere in recent 1 0,000 years shows that the warming in the 20th century may be the largest in recent 1 0,000 years, and in the 1990s it may be the warmest decade in recent 1 0,000 years, and in 1998 it was near/kloc-0. The observation data show that the annual average temperature in China is rising at the rate of 0.04℃ per 195 1~ 1989, showing an obvious upward trend. Since 1987, 14 has been unusually warm, and the warmest 1998 is 1.4℃. This warming trend is consistent with the global warming trend. The climate in China also shows obvious interdecadal characteristics, with a weak downward trend in the 1960s, a slow warming trend in the 1970s and early 1980s, and a significant warming trend in the late 1980s. Regionally, the warming in Northeast China, North China and the west of Northwest China is the most significant, especially in winter and in the evening than in the daytime.

Precipitation change

The precipitation in most land areas at high latitudes increases by 0.5% ~1.0% every ten years; North latitude 10 ~ 30, the rainfall in most land areas decreases by 0.3% every ten years; 10 N ~ 10 S the rainfall in the tropical continental area increases by 0.2% ~ 0.3% every ten years. Contrary to the northern hemisphere, similar systematic precipitation changes have not been detected in different latitudes in the southern hemisphere, which is related to the lack of sufficient data to determine the trend of precipitation changes.

The observation data show that in recent 50 years, the change trend of annual average precipitation in China is not significant, which is mainly manifested as obvious interannual change. The existing research shows that the annual average precipitation in China has a weak decreasing trend from 195 1 to 1989, but the regional differences are obvious, with the precipitation decreasing most seriously in North China, followed by the middle and lower reaches of the Yangtze River, East China and Southwest China. Precipitation increased obviously in the 1990s, but mainly concentrated in the middle and lower reaches of the Yangtze River, parts of South China and Northeast China.

Changes of climate extreme events

When the weather and climate in a certain place is abnormal, or the weather and climate in a certain place seriously deviates from its average state, it means "extreme events". According to the World Meteorological Organization, if the hourly, daily, monthly and annual values of a climate element reach more than 25 years, or the "difference" of the corresponding 30-year average exceeds twice the mean square deviation, the climate element is an "abnormal" climate value. Events with "abnormal" climate values are "extreme climate events". Events such as drought, flood, high-temperature heat wave and low-temperature chilling injury can all be regarded as extreme weather events.

After global warming, not only the average climate will change, but also the frequency of weather and climate extreme events will change. Although it is impossible to determine whether there is a consistent trend of extreme climate events on a global scale in the 20th century due to the serious shortage of observation data, some important "trends" have been found on a regional scale.

The observation records show that since 1950, the frequency of extreme minimum temperature has decreased, so the "frost day" and "freezing day" marking cold events have decreased; However, the frequency of extreme maximum temperature has increased. The observation records also show that there is an increasing trend of heavy rain and extreme precipitation events in areas with increasing precipitation in the middle and high latitudes in the northern hemisphere. In the second half of the 20th century, the frequency of heavy rainfall events in mid-high latitudes in the northern hemisphere may have increased by 2% ~ 4%. However, in the areas where precipitation decreases in the middle and high latitudes in the northern hemisphere, heavy rain and extreme precipitation events have a downward trend. In some parts of Asia and Africa, the frequency and intensity of droughts and floods have increased in recent decades. Analysis shows that some parts of the continent may become drier in summer, and the threat of drought may increase accordingly. In East Asia, although precipitation tends to decrease or change little, heavy rain and extreme precipitation events have increased in some places. The changes of storm intensity and frequency in tropical and subtropical regions of the world are still largely influenced by interdecadal changes, and there is no obvious trend of increase or decrease.

In recent 40 ~ 50 years, the extreme minimum temperature and average minimum temperature in China are on the rise, especially in northern winter. At the same time, the frequency of cold wave tends to decrease, the number of low temperature days tends to decrease, and the number of rainy days decreases obviously.

What will the climate be like in the future?

What will be the future scenario of global and China climate change? As mentioned above, there are many factors affecting climate and the mechanism is complex. Considering the influence of various factors, the current scientific level can not give the future climate prediction. We can only take the changes of greenhouse gases and aerosol concentrations in the atmosphere caused by human activities in the future as conditions and input them into the climate model to calculate the possible changes in the future climate. Climate change scenario is the difference between the possible future climate state and the current climate state. Next, let's talk about how the future climate will be different from the present climate.

Temperature change

According to the second assessment report completed by the Intergovernmental Panel on Climate Change in 1990 ~ 2 100, it is predicted that the global average surface temperature will be higher than that in 1990/0 ~ 3 in 2 100. This is equivalent to the global average temperature rising by 0. 10 ~ 0.35℃ every ten years.

According to the third assessment report completed by the Intergovernmental Panel on Climate Change in 20001,and 35 concepts of greenhouse gas and aerosol emission during the period of 1.000, it is predicted that the global average surface temperature will increase by about1.000 compared with that in 1.990. This is higher than the estimated value in the second assessment report, mainly because the estimated value of future increment of sulfur dioxide is far lower than that of 1995. In other words, the cooling effect caused by aerosols such as sulfur dioxide in the future is not as great as estimated in 1995. The warming rate of 0. 14 ~ 0.58℃ per decade is much higher than that actually observed in the 20th century, which may be unprecedented in recent 1000 years and will be a severe challenge to the adaptability of the ecosystem.

The degree of warming in almost all land areas may be higher than the global average, especially in winter in high latitudes in the northern hemisphere. The simulated warming values in Alaska, Canada, Greenland, northern Asia and Qinghai-Tibet Plateau are 40% higher than the global average. However, in summer in South Asia and Southeast Asia, and in winter in southern South America, the simulated warming value is lower than the global average.

It should be pointed out that in the future, the temperature changes in different parts of the world will be different, and the impact on the land surface will be faster than that of the ocean, and the sea surface temperature around the North Atlantic and Antarctica will rise less than the global average. Because the regional climate model is not perfect, the current regional climate change scenarios mainly use the prediction results of the global model.

Scientists in China used different global climate models to study the climate change scenarios in China after the increase of carbon dioxide, and the results were slightly different. Based on the five models in the Third Assessment Report of the Intergovernmental Panel on Climate Change, it is predicted that the annual average temperature in East Asia and China will increase by about 2 1, 966,5438+0 ~1,990℃ compared with the 30-year average. Assuming that carbon dioxide and aerosols increase at the same rate of 65,438+0% every year, it is predicted that the annual average temperature in East Asia and China will increase by about 3.9℃ by 265,438+09,665,438+0 ~ 65,438+0990.

Precipitation change

The third assessment report of the Intergovernmental Panel on Climate Change pointed out that after global warming, the global average precipitation tends to increase in 2 1 century, the average precipitation in most tropical areas will increase, the average precipitation in most subtropical areas will decrease and the precipitation in high latitudes will also increase. In terms of seasons, the precipitation in tropical Africa will increase in the northern hemisphere in winter, but it will not change much in Southeast Asia, and it will decrease in Central America. In summer in the northern hemisphere, there is little change in precipitation in South Asia. Summer precipitation in the Mediterranean and winter precipitation in Australia will decrease. In high latitudes, precipitation tends to increase in winter and summer. After climate warming, heavy rainfall events will increase. Because the increase of precipitation is not enough to balance the rise of temperature and possible evaporation, the central part of the continent will generally dry up in summer. In addition, the interannual variation of summer monsoon precipitation in the northern hemisphere may increase after climate warming.

It is predicted that the average precipitation will increase in most areas, and the precipitation may change greatly from year to year. Small changes in precipitation will cause great changes in water resources. This means that the possibility of drought increases, and more frequent droughts and floods may occur in some places. Summer precipitation in Central America and southern Europe is expected to decrease by 65,438+00% ~ 20%, which may be due to the constant number of precipitation days and the decrease of each precipitation, and more likely to be due to the significant reduction of the number of rainy days and the significant extension of the no-rain period. The model study on the influence of climate warming on precipitation in Australia shows that the total precipitation has not changed much, but the number of light rain days has decreased, the number of heavy rain days has doubled, and the probability of flooding has at least doubled.

The simulation research results of scientists in China show that only considering the annual growth rate of carbon dioxide 1%, it is predicted that the annual average precipitation in East Asia and China will increase by 0.1~1.74 mm/day in 1990. If carbon dioxide and aerosols increase at the same rate of 1% every year, it is predicted that by 2 100, the average annual precipitation in East Asia and China will decrease by 0.013mm/day compared with 30 years, from19,61~/kloc-0.

Climate extreme event change

In recent years, with the deepening of people's understanding of global climate change, scientists have begun to pay attention to whether the nature and frequency of climate extreme events are changing while paying attention to climate warming. The focus of attention is whether climate extreme events are more frequent, whether they are beyond the scope of natural climate change, whether they are related to climate change caused by human activities, and so on.

The ability to answer these questions is still limited. In its third assessment report, the Intergovernmental Panel on Climate Change only pointed out that the highest temperature in almost all land areas will increase and the number of high temperature days will increase. At the same time, the minimum temperature increases, and the number of cold days and frost days decreases accordingly.

The analysis shows that the extreme precipitation intensity in Europe, North America, South Asia, Sahara, South Africa, Australia and the South Pacific may increase. The threat of drought in Europe, North America, Australia and other regions has increased.

In some areas, the maximum wind speed of tropical cyclones may increase by 5% ~ 10%, and the average and maximum precipitation intensity brought by tropical cyclones may increase by 20% ~ 30%. However, there is no direct evidence that the frequency and generation area of tropical cyclones will change.

Uncertainty of climate change

Will the climate change in the direction predicted by scientists? Our answer now can only be three words "not necessarily". Because there are still many uncertainties about climate change. Now let's talk about these uncertainties. There is considerable uncertainty in the above climate change scenarios. The uncertainty of precipitation change scenario is greater than that of temperature change scenario. There are many reasons for uncertainty, mainly including:

(1) Uncertainty of greenhouse gas and aerosol emission data. Including the limited understanding of the source and flow direction of greenhouse gases, and the emission of greenhouse gases and aerosols is restricted by many factors such as population, economic and social development in various countries, which makes it quite difficult to accurately predict the concentration of greenhouse gases in the future.

(2) Due to the limited understanding of the physical and chemical processes of carbon cycle, greenhouse gases and aerosols, there is great uncertainty in transforming the concentration of carbon dioxide in the atmosphere into "radiation forcing" on the climate system.

(3) The defects of the climate model itself have a great influence on the study of future climate change scenarios. Predicting global and regional climate change in the next 50 ~ 100 years must rely on complex global air-sea coupling model and high-resolution regional climate model. However, the current climate model is far from perfect in describing clouds, oceans, polar ice sheets, etc., and the model cannot handle the influence of cloud and ocean circulation and regional precipitation changes.

(4) Extreme climate events rarely occur, and they are only marginally distributed statistically, which is easy to be confused with wrong data. At present, there is a lack of high-precision, high-resolution and long-term global observation data to identify the changes of climate extreme events. The current climate model can not be used to study the characteristics of small-scale climate extreme events. At present, it is impossible to distinguish the effects of natural factors and human activities on climate extreme events.

(5) As far as forecasting the future climate change scenario in China is concerned, the climate model suitable for China is still developing, and the foreign model used so far can not accurately construct the future climate change scenario in China, which is a great constraint for further studying the impact of climate change on China and the countermeasures that China should take.