Is there any conclusive evidence that human activities have caused global warming?

First of all, let's sum up that the global climate is constantly changing. From now on, the climate is many times colder than in the past! Unlike the highest vote answer, I try to talk about this issue from the perspective of history and literature.

1) Since 3500 years ago, China has been divided into Kyushu in Xia, Shang and Zhou dynasties. Among them, there is a "Henan" state, which is now the Henan area. The original meaning of the word metaphor is that a person pulls an elephant. Elephants lived in Xia, Shang and Zhou Dynasties in Henan, with a humid and warm climate. At that time, the temperature in Henan was similar to that in Yunnan now, and the climate was still relatively warm.

2) Push 1,000 years ago back to the Spring and Autumn Period and the Warring States Period more than 2,000 years ago. There is a sentence in the Book of Songs that says, "What's in the South?" There is a plum. "Zhongnan is Zhongnanshan, located in Shaanxi Province. Plum trees are warm, and there are plum trees in Zhong Nanshan near Xi 'an, which shows that the Qinling Mountains in Shaanxi are quite warm during the Spring and Autumn Period and the Warring States Period. As for Shaanxi now, why not try wearing down jackets in winter?

3) Push forward for more than 1000 years to the Tang Dynasty. In the Tang Dynasty, Du Fu once wrote a poem "Poetry of Sick Oranges", in which there is a saying, "A group of orange merchants, though many, are also ridiculous." This is a story about Li Longji, the emperor of the Tang Dynasty, growing oranges in Chang 'an. Although oranges don't grow well and the fruit is diseased, at least oranges can grow in the open air. It shows that the temperature in Chang 'an in Tang Dynasty was still higher than now. Now Xi 'an, let alone sick oranges, half-dead oranges are hard to survive. Du Fu also wrote, "Frost and snow accumulate in dark winter, and the situation is that the air blows back." It shows that although oranges can still survive at this time, the climate has begun to have frost and snow. At this time, the temperature in Chang 'an area is not as warm as before.

4) In the Song Dynasty, Kaifeng, the capital, never snowed all the year round. Prime Minister Sima Guang (yes, the one who smashed the jar) once wrote an article "Pray for Snow in the Temple", in which it was written that "there is no snow in winter and the heating is like spring". Even so, the temperature in the Song Dynasty was a little colder than before the Tang Dynasty. Because, Su Shi wrote a poem praising apricot: "Flowers send residual cold, fruit is new fire, but there is no plum in Guanzhong, and you are strong and full of harmony." Guanzhong area is Shaanxi area. At this time, there are no plums in Guanzhong area, which shows that although the climate in Song Dynasty is warmer than today, it has turned cold compared with that in Warring States. From these records in history, we can see that the climate is colder now than at some time before! As for the greenhouse effect and global warming, the best way is not to worry about what warming will lead to (after all, the ancients basically survived at higher temperatures), nor to worry about conspiracy theories, but to do scientific research in a down-to-earth manner and seriously come up with solutions to possible problems.