In many places, it has exceeded 30°C! As soon as spring comes, it is already summer? Is spring really getting shorter?

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CCTV News (Reporter/Yang Yifei): Recently, the temperature in many places has risen significantly, and the maximum temperature in some parts of South China and Southwest China has exceeded 30 °C. Many places in Yunnan Province have ushered in hot weather, and according to the local meteorological department, the maximum temperature will be close to 41°C in the next ten days.

On April 12, among the northern cities, the maximum temperature in Harbin and Changchun exceeded 20 °C, and the maximum temperature in Beijing, Tianjin and Shijiazhuang reached 26-29 °C, which was much higher than that of the same period in normal years.

Some netizens said, "I have the impression that the weather should be hot in May, but now it has begun to heat up early" "I feel that spring is getting shorter and shorter, and I only wear two sets of spring clothes and wear short sleeves"......

Is spring really getting shorter?

According to data released by the Shanghai Meteorological Service Center, the average number of days in spring was 72 days from 1900 to 1999, and from 2014 to 2018, the average number of days in spring was shortened to 70 days.

Spring in Beijing also tends to get shorter. Relevant data show that from 1951 to 1960, the average number of spring days in Beijing was 61 days, but from 2011 to 2017, the average number of spring days was only 50 days, and the rate of spring in Beijing decreased by about 1 day every 10 years.

Zhu Congwen, a researcher at the State Key Laboratory of Severe Weather at the Chinese Academy of Meteorological Sciences, said studies have shown that as global warming intensifies, spring is indeed getting shorter. "It was observed that the number of days of spring in the Northern Hemisphere in 1952 was 124. By 2011, the number of spring days in the Northern Hemisphere had been reduced to 115. 2023 is the warmest year since global warming, with record-breaking average temperatures around the world, which means that there will be significantly less time in the spring."

News+: What are the criteria for spring?

Zhu Congwen: There is more than one criterion for judging whether spring has arrived.

The earliest definition of spring was based on solar activity. The time of the spring equinox, autumn equinox, summer solstice, and winter solstice is defined according to the seasonal change of the sun's position, that is, the time of reaching the equator or the position of the Tropic of Capricorn. For example, the vernal equinox is generally around March 21, and from this day, we think that spring has arrived.

However, in different places, the temperature and season are different, so we often use the Gregorian calendar time in meteorology, defining spring as March to May, summer as June to August, autumn as September to November, and December to February as winter.

In addition, there is a definition, which we call phenology in academic terms, which refers to the time of year, the time of flowering, the time of growth, or the time of germination of crops. Perceive the changes of the four seasons according to the laws of farming.

In recent years, especially in the context of global warming, we have found that the four seasons have behaved differently than in the past, so the "Meteorological Industry Standards of the People's Republic of China" promulgated in 2012 set out meteorological standards for the division of climate seasons. It stipulates that the seasons are defined in terms of temperature changes. Spring starts at 10°C and ends at about 22°C, thus defining the whole spring. However, because the changes vary from day to day and year to year, in order to avoid the impact of temperature fluctuations on a certain day on a year, in the calculation process, the sliding daily average temperature definition is used, that is, spring is defined according to the 5-day moving average.

When the 5-day moving average is greater than 10°C, it is relatively stable, which is defined as the time when spring begins, and the time after 22°C is the end of spring and the beginning of summer.

News+: Is spring really getting shorter?

Zhu Congwen: The length of spring varies from place to place. In the south, such as southern China, spring lasts the longest, and relatively speaking, the further north you go, the shorter spring is. Standing in different places to understand the length and shortness of spring, the feeling is different.

According to the records of the past few decades, in China, the most significant places for global warming are in the subtropics, in the middle and high latitudes. In the north, especially in Inner Mongolia, as well as in Beijing, Tianjin, and Hebei, it is very obvious that the temperature rise is much greater than that in the south, which is a characteristic.

Second, in terms of the rate of warming, the rate of warming has accelerated significantly since 1985, and the rate of warming in China is 1.5-2 times that of the global average temperature.

So the seasonal changes in our area are very noticeable, and this change is something that everyone can feel, and it is also the reason why many people have the feeling that "spring is getting shorter", and this feeling is not inaccurate.

A study by Guan Yuping's team at the South China Sea Institute of Oceanology of the Chinese Academy of Sciences answers the question of changes in the length of spring. He divided the temperature into four equal parts, and defined the time of the beginning and duration of spring, summer, autumn, and winter according to the thresholds corresponding to the four equal parts.

Across the Northern Hemisphere, the observed duration of spring in 1952 was 124 days, 78 days in summer, 87 days in autumn and 76 days in winter. By 2011, there were 115 days in spring, 95 days in summer, 82 days in autumn and 73 days in winter.

This reflects the fact that spring is shorter, summer is longer, and autumn and winter are also getting shorter.

2023 is the warmest year since global warming, with global average temperatures breaking historical records, which means that there will be significantly fewer springs (regional variations).

In the future, at this rate, under the strongest emission scenario, spring will become 108 days by 2100, summer will be longer to 166 days (up to nearly six months), autumn will become 60 days, and winter will become 31 days.

Shorter spring doesn't mean it's the shortest of the four seasons. Historical records show that spring is the longest of the four seasons (in the case of the entire northern hemisphere subtropics) and that winter is the shortest, but with global warming, spring is the most sensitive and significant change relative to past standards.

News+: What are the effects of a shorter spring?

Zhu Congwen: Spring becomes shorter and summer becomes longer, which does not mean that the temperature is warm as spring every day. Through observations over the years, there have been many extreme weather, such as a strong cooling and cold wave on a certain day in winter. In the past, there were few days in which the temperature dropped to 10 degrees or 8 degrees in 24 hours, but in the last 10 or 20 years, the temperature has dropped to 18 degrees or 20 degrees in 24 hours, and the temperature fluctuations have increased, which means that this extremity is increasing.

We can also see this seasonal change from a dynamic perspective. In the future, the previous seasonal classification standard is no longer applicable in the context of climate change, and the distribution characteristics of the seasons in the context of climate change can be re-understood by changing the standard.