Nearly 40 years ago, Congress passed legislation to control air pollution and clean up our skies. The Clean Air Act and its subsequent revisions have been widely successful at cleaning up the atmosphere and improving the quality of the air we breathe. After nearly a half-century of new scientific inquiry and discovery, we have a better understanding of the natural world. We need to update our laws to recognize and regulate anthropogenic carbon dioxide and other greenhouse gases for what they truly are: pollutants.

Labeling carbon dioxide and other greenhouse gases as air pollutants might seem strange, but these gases have all of the characteristics associated with traditional air pollutants, such as sulfur dioxide or lead. These anthropogenic gases are emitted as a byproduct of human activity. They accumulate in the atmosphere and cause harm to humans, animals and plant life.

The latest Intergovernmental Panel on Climate Change assessment report clearly lays out the case. The world emitted 49 gigatonnes of carbon dioxide anthropogenic greenhouse gases in 2004. Carbon dioxide concentrations in the atmosphere reached 379 parts per million (ppm) in 2005 and showed no signs of slowing. Climate change is already causing problems, such as ecosystem disruption and glacial melting.

Classifying all greenhouse gases as pollutants similar to carbon monoxide may seem unreasonable to some. Carbon dioxide is a naturally occurring molecule that is a necessary component of plant life on this planet. How can it be a pollutant?

Other life sustaining compounds can become deadly. Vitamin A is a necessary component of our diets. Ingest too much Vitamin A, and it will become toxic. In the same way that the excessive intake of certain vitamins and minerals will hurt rather than help the body, excessive emission of greenhouse gases damages the planet.

It would also seem contradictory to single out anthropogenic emissions as pollutants when so many greenhouse gases have natural origins. Since carbon dioxide is released during respiration, it would appear to criminalize the very act of breathing. However, only greenhouse gases emitted above the amount the planet can handle fall under the definition of a pollutant.

The situational nature of an air pollutant is not unprecedented. The ozone is a necessity high above our heads in the stratosphere, where it blocks dangerous UV light from reaching the Earth’s surface. Move that ozone down to the ground, and it causes damage to human health and property.

This classification is also supported by a U.S. Supreme Court decision. On April 2, 2007, the Supreme Court ruled that carbon dioxide and other greenhouse gases fit the description of an “air pollutant” as defined in the Clean Air Act. While not requiring the U.S. Environmental Protection Agency (EPA) to implement any particular program, it did settle the legal debate on whether the government had statutory authority to regulate these emissions as air pollutants.

Evidence collected over the past half-century overwhelmingly supports the idea that anthropogenic greenhouse gases are air pollutants and that government has the right to restrict their emissions. The U.S. EPA is already starting the rule-making process to regulate these gases, regardless of congressional action. This process has greatly reduced the concentration of many traditional air pollutants across the nation. However, newer programs such as “Cap and Trade” are better suited to reducing greenhouse gas pollution cheaper and more quickly than EPA command and control regulation. It would be a shame if Congress prevented this from happening due to political expedience and ignorance.

As the second anniversary of the Supreme Court decision recognizing the U.S. EPA’s authority to regulate greenhouse gases approaches this week, we need to update our vocabulary. Carbon dioxide, methane, nitrous oxide and other compounds related to climate change are not just greenhouse gases anymore. They are air pollutants, and we need to start treating them as what they truly are.

Reach columnist Mike Noon at opinion@dailyuw.com.