Which of the following is NOT true of greenhouse gases?

The statement regarding greenhouse gases that is not true is that they are produced solely by human activities. Greenhouse gases, which include carbon dioxide, methane, water vapor, and nitrous oxide, have both natural and anthropogenic (human-caused) sources.

Natural processes such as volcanic eruptions, respiration from living organisms, ocean-atmosphere exchanges, and decomposition also contribute significantly to the presence of these gases in the atmosphere. For example, water vapor is the most abundant greenhouse gas and is primarily produced by natural processes like evaporation. Therefore, the idea that greenhouse gases are produced only by human activities does not accurately reflect the complexity of their sources.

The other statements about greenhouse gases are true. They absorb Earth's radiation, helping to regulate the planet's temperature. They are also transparent to incoming solar radiation, allowing sunlight to enter the atmosphere while trapping some of the heat that radiates back from the Earth’s surface. Finally, they indeed include substances like carbon dioxide and water vapor, which play crucial roles in the greenhouse effect and climate regulation.