Why isn't the weather getting warmer?

According to meteorological weather, there are four seasons: when the average temperature of the day is above 10℃ for five consecutive days, it means the arrival of spring. In the history of Beijing, this standard was generally reached in early April of the Gregorian calendar. An agricultural proverb in Beijing says, "Don't shoot in September, walk on the ice in March and April, look at the green willows by the river in May and June, open the river in July and September, geese come in August and September, catkins fall in September and cows walk everywhere." Historically, the spring climate in Beijing was in the late March of Gregorian calendar (starting on March 23rd and 4th), and the temperature was basically stable above 10 degrees in the early April of Gregorian calendar. In other words, it basically takes nearly two months.