How has the earth's climate changed in the past?

Answer 1

For the past twenty million years the climate changed in response to orbital variations known as "Milankovitch Cycles." This entailed a series of ice ages. These ice ages may have been precipitated by what is known as the "Azolla Event," which began about 15 million years after the end of the Cretaceous.

Azolla is a freshwater fern which sank into the icy depths of the Arctic ocean. Over a fairly short period of a few hundred thousand years billions of tons of atmospheric carbon was sequestered onto the sea floor by the growth and death of this fern. The climate cooled, and thus began the last series of ice ages.

Answer 2

The Earth's climate has changed naturally over millions of years due to factors like changes in the Earth's orbit and volcanic activity. In recent history, human activities such as burning fossil fuels have led to significant changes in the climate, resulting in global warming and climate change. This is evidenced by rising global temperatures, melting ice caps, and more frequent extreme weather events.