Q: How do human activities affect the carbon cycle?

Flexi Says: Humans have changed the natural balance of the carbon cycle because we use coal, oil, and natural gas to supply our energy demands. Fossil fuels are a sink for CO₂ when they form, but they are a source for CO₂ when they are burned. So when a car burns a tank of gas, the amount of CO₂ in the atmosphere increases just a little. Added over millions of tanks of gas and coal burned for electricity in power plants and all of the other sources of CO₂, the result is the increase in atmospheric CO₂. The second largest source of atmospheric CO₂ is deforestation. Trees naturally absorb CO₂ while they are alive. Trees that are cut down lose their ability to absorb CO₂. If the tree is burned or decomposes, it becomes a source of CO₂. A forest can go from being a carbon sink to being a carbon source if trees are not growing back faster than they are dying off or cut.