What is climate change?

Geological evidence shows that in the whole natural history of the earth, at least nine tenths of the time is dominated by warm climate, such as early Paleozoic, from Cambrian, through Ordovician, Silurian to Devonian, which is 250 million years long; During the whole Neogene period of about 200 million years from Mesozoic to Cenozoic, the climate was mainly warm, and of course it also included several short cold periods (ice ages).

It is difficult to confirm the duration and influence scope of the ice age interruption period, but only from the study of stratigraphic sediments, it seems that there were great ice ages in Precambrian (600 million years ago), Carboniferous and Permian (350 million to 225 million years ago).

In the last one million years, the cold climate dominated, that is, the Quaternary Great Ice Age. The arctic ice sheet has greatly extended to the mid-latitude area, reaching 57 degrees north latitude at the strongest time, and the thickness of the ice sheet in some places has reached 2 kilometers.

There was a warm interglacial period in the middle of the Great Ice Age, and the change of cold and warm climate led to the rise and fall of glaciers. The study of glacial landforms in the European Alps shows that the Quaternary glacial period is divided into four glacial periods, separated by three relatively warm interglacial periods. Compared with the interglacial period, the snow line in the mid-latitude area can rise and fall by more than 1200m.

Among the fossils unearthed from Quaternary sediments in northern China, there are creatures representing cold climate and warm climate. The former is rhinoceros hair, mammoth, saxifrage and shade fern, while the latter is rhinoceros, buffalo, elm and willow, which proves the climate change in China in Quaternary.

Another example is loess deposition and its underlying red soil layer, which is widely distributed in northwest and north China, showing a change from warm climate to cold and dry climate. In Quaternary, glaciers were distributed not only in the western mountainous areas of China, but also in Taibai Mountain in Qinling Mountains in the middle and east and Yushan Mountain in Taiwan Province Province.

About 1 10,000 years ago, the climate warmed, glaciers retreated, and the earth once again entered a warm interglacial period.

Climate change in human history;

After the Great Ice Age, the climate in most parts of the earth was the warmest before 5000~ 3000 BC, which was considered as the best period after the Ice Age. At that time, the sea level was 2~3 meters higher than it is now, and the ice in the Arctic Ocean may melt completely in summer. Now the Sahara desert in Africa and the desert in the Middle East, the climate at that time was much wetter.

From 900 to 450 BC, before the so-called early Iron Age, the climate in Europe entered a cold and humid period, and the glaciers in the Alps expanded significantly. Many peat profiles from Ireland to Germany show that swamps were distributed in this vast area 2500 years ago; Most of the modern glacial remains found south of 50 degrees north latitude in the North American Rocky Mountains were formed during this period.

From 1000 to 1200, the climate in the northern and southern hemispheres has been in a suitable warm state, which is also called the "second climate optimum period". At that time, the temperature in southern Greenland should be about 4 degrees Celsius higher than it is now. Due to the suitable climate, the vikings immigrated to Greenland in 982 AD.

From 1430 to 1850, the climate in the northern hemisphere turned cold, especially from 1650 to 1750, which was called the "Little Ice Age". With the cold climate, the humid mid-latitude zone and the increase of rainfall, the water level in the Caspian Sea is more than 5 meters higher than that in previous and later centuries. After 1850, the climate showed a warming trend again.

With the improvement of modern scientific observation, the study of climate change has a reliable data base, and its scientific principles are gradually revealed.