Earth's climate history alternates between ice and fire. The current ice age that humans are in (with ice caps at both poles) is rare in the 4.5 billion-year history of the earth. Most of the time, the earth is an ice-free warm world.
During the Cretaceous Period 66 million years ago, the global average temperature reached 36°C and the polar sea temperature reached 27°C. Dinosaurs thrived in a warm environment. However, not all warm periods are so hospitable - at the end of the Permian 270 million years ago, super volcanic eruptions caused global temperatures to rise by 10°C, triggering the most severe mass extinction event in the history of the earth, with 95% of marine life and 70% of terrestrial life disappearing.
Earth's temperature regulation relies on the "carbon cycle": carbon dioxide is absorbed into rocks through chemical weathering and re-released through volcanic activity. This mechanism has allowed the earth to maintain a relatively stable climate for a long time, but it has also gone out of control many times. 2.4-2.1 billion years ago, the Earth experienced a "Snowball Earth" event, with ice sheets covering the entire planet and temperatures as low as -50°C. Scientists speculate that this may be due to photosynthetic microorganisms consuming methane (the main greenhouse gas at the time), causing runaway global cooling. At the end of the Permian period 252 million years ago, Siberian volcanoes erupted for one million years. Carbon dioxide caused the temperature to rise sharply by 10°C, leading to the extinction of 95% of marine species - the Smithsonian Institution called this the "worst mass extinction."
Since the industrial revolution, human activities have rapidly changed the earth's climate. Atmospheric carbon dioxide concentration has increased from 280ppm to 426ppm, and the global average temperature has increased by 1.47°C. . If emissions continue, they may reach 600-1000ppm in 2100, raising temperatures by 4°C. A similar situation occurred during the Paleocene-Eocene Thermal Maximum (PETM) 55 million years ago, when global temperatures were 5-8°C higher than today and ecosystems were drastically reorganized.
In the future, the Earth’s “carbon thermostat” will eventually fail. In about 500 million years, carbon dioxide concentration may fall below the survival threshold of plants; in 1 billion years, as the sun becomes brighter, the earth will enter an irreversible period of extreme high temperatures, and life will face severe challenges.
Humans are pushing the Earth into unknown territory, but history shows that the Earth will eventually recover—but it may not leave traces of human civilization.