Question

Carbon dioxide enters the atmosphere by animal and human

Answer 1

Emission. Remember that we humans breathe in oxygen, and we breathe out carbon dioxide.

Answer 2

Carbon dioxide (CO2) is released from various sources such as living beings, industries, automobiles, burning of fossil fuels, etc.
Respiration from plants and animals.
Decay of plant and animal matter. This converts to carbon dioxide in the presence of oxygen, or into methane if there is no oxygen.
Burning of any organic material oxidizes the carbon to produce carbon dioxide.
Burning fossil fuels releases CO2 that has been stored for millions of years.
Burning biofuels releases CO2 that has been stored for only a few years, or less.
Production of cement. When limestone is heated to produce lime, CO2 is released.
As the oceans become warmer, CO2 is released from the surface.
Volcanoes emit water vapor, CO2 and sulfur dioxide. Silicate weathering is a process that removes CO2 and the two processes, the chemical reverse of each other, cancel each other out.