I wonder if you have the illusion that spring seems to be getting shorter and shorter over the years? Many times the winter is just over, and the summer is ushered in, and it feels like the length of the two seasons of spring and autumn is not as long as the length of winter and summer!
Now you don't have to doubt yourself, scientists have confirmed that spring is indeed getting shorter, and in recent years spring has become shorter and faster, so what is going on?
Spring becomes shorter
In fact, there are two definitions of spring, one is based on the definition of the 24 solar terms, which stipulates that the period from spring to summer is called spring. However, meteorology usually uses the "weather average temperature method", that is, the average temperature for 5 consecutive days is greater than 10 °C and below 22 °C, and at the same time, it is recognized as spring at the end of winter. Nowadays, the temperature in many parts of the mainland has reached the standard of spring, and many places in the south have officially entered spring.
The study found that whether it is the definition of spring by the 24 solar terms or the "average weather method", spring is slowly shortening.
The first is the definition of spring by the 24 solar terms, which the study found that spring in the Northern Hemisphere becomes shorter by 30 seconds each year, while summer becomes longer and longer. What's going on?
It turns out that this matter is related to the orbit of the earth, and the orbit of the earth around the sun is not round, but elliptical, and there are perihelion and aphelion points.
Among them, in early January of each year, the Earth is closest to the Sun, which is the perihelion, and in early July every year, the region is the farthest from the Sun, which is the farthest point. January is the winter and spring season in the Northern Hemisphere, while July is the summer season in the Northern Hemisphere.
When the Earth moves to perihelion, the rotation speed is relatively fast, so the spring in the northern hemisphere will be shortened; at the far point, the Earth's rotation speed is slower, and the summer in the northern hemisphere will be extended.
According to the researchers, in 2015, the number of spring days in the northern hemisphere was 92.76 days, and by 3000 it would become 91.97 days; in 2015, the number of summer days was 93.65 days, and by 3000 it would become 93.92 days.
It is just that the means of delineating spring by 24 solar terms are too simple and crude, the continent is vast, the climatic conditions are different, and the time of spring and the end of spring is different in different places, so in meteorology, we usually use the "average temperature method" to determine spring.
However, according to the "average weather method", people have also found that spring is slowly shortening, especially in recent years, and the rate of spring shortening has accelerated.
Short spring neck
There is an old Chinese saying that "spring neck is short", which means that spring is relatively short, and it will pass in the blink of an eye.
The China Weather Network once made a statistic on the number of spring days in the Beijing area, and from the record statistics since the meteorological period in 1951, it was found that spring was indeed getting shorter and shorter, of which there were 61 days in the spring of Beijing from 1951 to 1960, but the average number of days in the spring of 2011-2017 was only 50 days. Spring in Beijing is decreasing at a rate of about 1 day every 10 years.
Of course, even in the period from 1951 to 1960, the number of days that lasted in spring was only 61 days, and it is reasonable to say that the spring in Beijing with four distinct seasons should be 90 days, so why is there so many fewer days?
This is actually because, in different regions, the four seasons are not evenly distributed, with almost no winter in the tropics, and very few days in the polar regions, and the number of days that last in spring, summer, autumn and winter is different at different latitudes.
But in the same region, it is reasonable to say that the number of days that lasts in the spring is almost the same, but why is spring gradually shortening in these years?
Researchers at the National Climate Center of the China Meteorological Administration once introduced that because of global warming, most parts of the mainland have a trend of spring in advance, and from the overall trend, the spring will continue to advance in the future. At the same time, the duration of spring has been shortened a lot.
The first is that global warming will cause glaciers in the polar regions to melt, the area of sea ice to shrink, so that the rate of warming in the polar regions will increase, and the polar warming will reduce the pressure gradient forces of the polar regions and the equator, making it easier for cold air to move south and become colder in winter.
Secondly, global warming leads to a significant warming over the East Asian continent in the spring, and the difference in sea and land heat in East Asia is large, resulting in an early transition from winter wind to summer wind, which is easier to heat up and easier to enter summer.
It is precisely because of this that the spring sandwiched between winter and summer is getting shorter and shorter, and the spring time is earlier.
If global warming continues, spring may become shorter in the future, extreme weather will become more extreme, and even threaten the survival of human beings.