Final answer:
Carbon sequestration is not a way carbon can return to the atmosphere; it is a process of capturing and storing atmospheric carbon dioxide. The other options listed, deforestation, fossil fuel combustion, and volcanic eruptions, all contribute to the release of carbon into the atmosphere.
Step-by-step explanation:
The option that is not a way carbon can return to the atmosphere is d) Carbon sequestration. Carbon sequestration refers to the process of capturing and storing atmospheric carbon dioxide. It is the opposite of releasing carbon into the atmosphere. The other options listed, such as a) Deforestation, b) Fossil fuel combustion, and c) Volcanic eruptions, all involve releasing carbon back into the atmosphere. Deforestation leads to fewer trees that can take up carbon dioxide, thereby increasing atmospheric carbon when the trees are burned or decompose. The combustion of fossil fuels releases stored carbon as carbon dioxide, which is a significant contributor to the atmospheric carbon dioxide levels. Volcanic eruptions release carbon gases trapped beneath the Earth's surface.
Carbon sequestration includes natural processes like the absorption of CO2 by forests (reforestation) and oceans or by artificially injecting CO2 underground where it won't immediately re-enter the carbon cycle. Examples of this include technologies that capture carbon at the source of emission and store it, instead of releasing it into the atmosphere. These efforts are made to reduce the impact of greenhouse gases on global warming.