We have created this problem by burning fossil fuels.
These are fuels produced in the earth from plants and animals.
People have always used natural products as fuels.
In previous eras, people used wood and coal, largely for cooking and heating, and this created carbon dioxide.
But with the coming of industry and the discovery of oil under the ground, the amount of carbon dioxide began to increase at a significant rate.
Today, as more and more countries develop, this increase is speeding up.