Carbon dioxide (CO2) is a gas essential for life—animals exhale it, plants sequester it. It exists in Earth’s atmosphere in comparably small concentrations, but is vital for sustaining life. CO2 is also known as a greenhouse gas (GHG)—a gas that absorbs and emits thermal radiation, creating the ‘greenhouse effect’. Along with other greenhouse gases, such as nitrous oxide and methane, CO2 is important in sustaining a habitable temperature for the planet: if there were absolutely no GHGs, our planet would simply be too cold. It has been estimated that without these gases, the average surface temperature of the Earth would be about -18 degrees celsius.1
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