Carbon dioxide (CO2) is a natural component of the Earth's atmosphere and plays a crucial role in the planet's carbon cycle, which is the process by which carbon circulates among the atmosphere, oceans, soil, and living organisms. Nature contributes to atmospheric CO2 in several ways:

1. Respiration: All animals and plants respire, releasing CO2 into the atmosphere. In the process of cellular respiration, oxygen is used to break down food substances to produce energy, water, and CO2.
2. Decomposition: When plants and animals die, their bodies, wastes, and remains are broken down by microorganisms, a process called decomposition. This process releases CO2 back into the atmosphere.
3. Natural fires: Natural events such as wildfires or volcanic eruptions release large amounts of CO2 into the atmosphere. While wildfires burn plant material and release CO2, volcanic eruptions release CO2 trapped in the Earth's crust.
4. Ocean release: The world's oceans contain a vast amount of CO2, dissolved in the form of bicarbonate and carbonate ions. When sea surface temperatures rise, the ocean releases CO2 into the atmosphere. This is because the solubility of CO2 decreases as the temperature increases.
5. Soil respiration: Soil organisms, including bacteria, fungi, and earthworms, break down organic material in the soil and release CO2 as a byproduct.

These natural processes have been occurring for hundreds of millions of years and have shaped Earth's climate. For most of this time, the carbon cycle has been in balance, with roughly the same amount of CO2 being absorbed by plants and the oceans as is released by respiration, decomposition, and other processes.

However, human activities, particularly the burning of fossil fuels (coal, oil, and natural gas) and deforestation, have significantly increased the amount of CO2 in the atmosphere, disrupting this balance and leading to a rise in global temperatures, a phenomenon known as global warming. This is because CO2 is a greenhouse gas, meaning it traps heat from the sun and prevents it from escaping back into space.

While nature contributes CO2 to the atmosphere, it also plays a critical role in removing it. Through a process called photosynthesis, plants and algae take in CO2 from the atmosphere and convert it into oxygen and sugars. The world's oceans also absorb a significant amount of atmospheric CO2. Therefore, protecting and restoring natural habitats like forests, wetlands, and coral reefs is an important part of mitigating climate change.