World Meteorological Organization Secretary General Talas once said that extreme weather events have become the norm. This means that more severe extreme high temperature, rainstorm, flood and other disasters will occur more frequently, affecting and even threatening all life on the earth.

The data shows that the 50 years since 1970 are the warmest since 2000; In 2021, the global carbon dioxide concentration will be 415.7 ppm (one millionth), and it is still increasing, reaching the highest level since 2 million years; In the last 10 years, the average annual sea ice area in the Arctic has shrunk to the lowest level since 1850; Since 1900, the global average sea level has risen faster than any century in the past 3000 years.

The warming of the climate system will last at least until the middle of this century. In the next 20 years, the global temperature rise (compared with the level before industrialization) will reach or exceed 1.5 ℃.

In the context of climate change, the water cycle will also be strengthened. The increase of land precipitation is higher than that of ocean or global average, and the monsoon precipitation is expected to increase globally, especially in South Asia and Southeast Asia, East Asia and West Africa except the western end of the Sahel. In areas dominated by snowmelt runoff, snowmelt will be earlier in the future spring, and the peak runoff will also increase. In the Pacific islands, as well as in many parts of North America and Europe, heavy rainfall and resulting floods will become stronger and more frequent. In some regions of Africa, South America and Europe, the frequency and severity of agricultural and ecological drought will also increase.

In addition, mountain and polar glaciers will continue to melt for decades or hundreds of years in the future, and the Arctic may be ice free at least once in September before 2050. Due to the continuous warming of the deep sea and the melting of the ice sheet, the sea level will also continue to rise for hundreds to thousands of years, and the sea level change will lead to the erosion of most sandy coasts.

At the same time, the probability of concurrent extreme weather and climate events and complex events in many regions of the world will increase, such as the concurrent occurrence of high temperature, heat wave and drought, and the superposition of extreme sea level and heavy precipitation will lead to the intensification of complex flood events.

At present, climate change has caused a wide range of adverse effects, involving water, ecosystem, health, economy and other aspects of natural and social systems. Since the 1950s, about 10% of the global population has been affected by the increase of heavy rainfall or drought events. About 4 billion people in the world experience severe water shortage for at least one month every year. About half of the more than 4000 species in the world have migrated due to climate change, and two-thirds of the spring phenology occurs ahead of schedule. The threat of climate change to climate sensitive diseases, malnutrition and mental health is increasing. In addition, heat waves, floods and droughts have reduced grain production, thereby endangering food security.

In the future, a variety of climate change related risks faced by natural and social systems will further intensify. It is estimated that when the global temperature rises to 1.5 ℃, the proportion of species facing high risk of extinction in the terrestrial ecosystem will reach 14% at most, and will further rise to 18% and 29% at 2 ℃ and 3 ℃. There may also be some irreversible risks in water resources and ecosystems, such as the melting of low altitude glaciers, the loss of biodiversity and ecosystem services caused by exceeding the tolerance threshold of organisms, etc. (The author is Han Zhenyu, deputy director and researcher of the Climate Change Impact Adaptation Office of the National Climate Center)