In 2007, a divided Supreme Court ruled that the Environmental Protection Agency must treat carbon dioxide and other greenhouse gases as “pollutants,” and must therefore analyze whether the increasing concentrations in atmospheric carbon might reasonably be anticipated to endanger human health and welfare. The court may be on the verge of facing this issue once again.

To be clear, the court did not mandate regulation in 2007; rather, it mandated that the EPA go through what is known as an “Endangerment Finding” process. The EPA did so and on Dec. 15, 2009, issued its ruling that carbon dioxide and other greenhouse gases must be regulated. This EPA finding and associated rulings were immediately challenged in the federal D.C. Circuit Court, which initially ruled in favor of the EPA.