Shulou(Shulou.com)11/24 Report--

On July 27, at the United Nations headquarters in New York, Secretary-General Guterres warned of climate change: "the era of global warming is over and the era of global boiling has come." On the same day, the World Meteorological Organization and the European Commission Copernicus Climate change Service said July witnessed the hottest three weeks on record and the hottest three days on record. Has global warming reached such a critical point?

01. Rising temperatures at the beginning of 2023, the global average temperature was 0.73 ℃ higher than the historical average. However, until May, the global average temperature in 2023 was still on a par with that in 2022, and experts from different agencies still agreed on whether the temperature could reach a new high in 2023. But the situation changed in May. According to the University of Maine Climate reanalysis system, temperatures in 2023 exceeded the same period in 2022 from May 10, 2023. By early June, the average temperature in 2023 had reached an all-time high. On July 3, the global average temperature of 2 meters above the earth's surface reached 17.01 ℃, the hottest day on record, which lasted until July 6, setting a record of 17.23 ℃ and + 1.02 ℃ above average temperature. If calculated from the beginning of June, this "highest temperature" has been achieved on and off for more than a month.

Figure 1 the orange line shows the temperature in 2022, and the black line shows the temperature on July 7, 2023, and the global temperature began to drop, but in the high temperature northern hemisphere, this trend did not abate, and on July 25, the northern hemisphere warmed up for nearly a month with a record of 22.62 ℃ higher than the average temperature of 1.23 ℃. In China, the highest temperature in an area of millions of square kilometers reached 37 degrees or above on July 10, and this area will expand a lot considering the addition of the urban heat island effect. In Europe, temperatures in Spain and France have been more than 10 ℃ higher than in previous years due to the heat wave in North Africa since June.

Fig. 2 the mean temperature in the northern hemisphere corresponds to the air temperature. Compared with the air, the warming efficiency of sea water is lower and the range of temperature change is small, but most of the heat from climate warming is stored in the ocean. In the 1980s and 1990s, the climate warming theory was questioned because of the slowdown of climate change, and later studies found that the ocean acted as a buffer. However, in 2023, the ocean could not contain its own warming trend, breaking the SST record with a record of 21.1℃ and staying above 20.9 ℃ for a long time, far exceeding the average temperature of 20.6 ℃ and 20.2 ℃ in 2022.

02. Is climate warming natural or man-made? However, the human climate record has not been more than 200 years, and it is a bit beyond our control to talk about global warming only with a 200-year record. Therefore, climatologists try to look for evidence from history. In 1972, Chinese scientist Zhu Kezhen published "the preliminary study of Climate change in China in the past 5,000 years". This paper restores the climate change in Chinese history by means of archaeology, phenology and documentary recording. it is also pointed out that the temperature in history is higher than that of today, which has become the most familiar article on climate change among the Chinese public in the past 50 years.

Fig. 3 Zhu Kezhen curve Zhu Kezhen's article is only one part of many paleoclimate studies. Scientists represented by Milankovich have discovered a series of climate cycle theories, among which the Milankovich cycle has a complex doll cycle ranging from 400,000 to 23,000 years. Under such large-scale periodic changes, the role of human beings does not seem to be worth mentioning. Therefore, in recent years, with the deepening of paleoclimate research and the popularization of research results, climate warming is a natural process rather than a man-made result.

On the one hand, paleoclimate studies have found that compared with the long-term climate evolution of the earth, the global climate change since the Industrial Revolution is small; on the other hand, scientists have also found that compared with the subject matter of climate change in the historical period, today these subjects are changing much faster than in the historical period. Obviously, with the increase of human greenhouse gas emissions, the impact of human activities on climate change will increase day by day.

03, global warming and extreme weather, whether global warming is a natural phenomenon or man-made cause, warming has become an indisputable fact. People are more likely to feel climate change-extreme weather-from an intuitive experience than digital alienation.

Last year and this year, North China experienced temperatures rarely seen in history; in late July and early August, under the influence of typhoons "du Suri" and "Kanu", heavy rain fell in North China, breaking historical records in many places; and in July 2021, under the influence of Typhoon "fireworks", heavy rain fell in central and northern Henan, causing extremely tragic disasters. Looking around the world, wildfires, floods, droughts and heat waves occur frequently. Is this the result of the spread of social media? Or is it a normal phenomenon of normal climate fluctuations? Or is it the result of climate change? To find these answers, we also need to look for answers from the mechanisms that cause these climate anomalies.

Fig. 5 extreme precipitation in Beijing, Tianjin and Hebei take the high temperature in North China as an example, the main reason is that the continental warm high pressure ridge, affected by the warm high pressure ridge, the air current sinks, the weather is clear, and the temperature is further heated to form a high temperature. Figuratively speaking, it is a thermal dome, like a cover covering North China. In essence, the formation of this thermal dome comes from the bending of the westerly belt.

The power of the westerly belt comes from the temperature difference between high and low latitudes. The greater the temperature difference, the stronger the westerly wind. It is like a belt that separates the polar regions from the equator. With global warming, there is less sea ice in the Arctic, and dark sea water further absorbs solar heat to increase temperature, which reduces the temperature difference on both sides of the westerly belt, resulting in a weakening of the westerly jet and an increase in the frequency of cold and warm air flow. The westerly belt is more likely to form large troughs or ridges, causing a variety of extreme weather events. Therefore, there will be more rather than less hot weather like North China in the future.

Fig. 6 the westerly jet (NASA) at the same time, the weakening of the westerly belt will also make the cold air more likely to invade south, which increases the possibility of the cold wave breaking out; at the same time, the warm air is more likely to invade the polar regions, thus further increasing the intensity of the cold wave. Coupled with the rise in average temperatures caused by global warming, the damage caused by this cold wave will be even greater.

Recently, an article published in Nature Communications suggested that the Atlantic Meridional reversal Circulation (AMOC), including the Gulf Stream, could turn towards full collapse between 2025 and 2095 because of global climate change. AMOC plays an important role in maintaining global temperature balance, and its collapse will further aggravate the occurrence of extreme weather. Although there are still many uncertainties in the study of this article, it still provides us with a warning worthy of attention.

Fig. 7 A simplified animation of the global AMOC "conveyor belt". The surface currents are shown in red, and the deep-sea currents show Guterres's "global boiling" in blue. Although it is an exaggeration, if climate change continues at the current rate, the earth will not boil, but human society may be "boiling".

reference

Tierney J,Poulsen C,Montanez I et al. Past climates inform our Future.Science, 2020, 30 (6517).

Ditlevsen, P., Ditlevsen, S. Warning of a forthcoming collapse of the Atlantic meridional overturning circulation. Nat Commun 14, 4254 (2023).

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Xing Si

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