The Supreme Court’s climate decision, explained

It worked. America’s air got much cleaner and, while there are still emissions of small particles and ozone, things improved. The law was effective.

In recent decades, though, a new form of emission emerged as a risk to public health: greenhouse gases. For years, heavy industry produced air pollution that made individuals sick directly. Now the attention of the scientific community turned to emissions that helped blanket the planet with heat-trapping gas, endangering humanity broadly.

We don’t usually think of carbon dioxide — the most common greenhouse gas — as a pollutant. We exhale carbon dioxide; we don’t exhale smog. But then, not everything we emit from our bodies is something we think should simply be allowed to constantly surround us. This is why we have sewer systems. So attention turned to this different form of pollutant.

Sign up for How To Read This Chart, a weekly data newsletter from Philip Bump

When climate change first became a subject of public attention about 15 years ago, there was a push for congressional legislation that would establish a mechanism for limiting carbon dioxide in particular. The primary source of carbon dioxide emissions is the generation of electricity; specifically, burning coal. So Congress debated various ways to limit coal-burning, including a system in which carbon dioxide emissions would become part of a marketplace, letting emitters — polluters, if you will — trade the ability to produce carbon dioxide the way someone might trade stock.

But the emergence of climate change as a political priority soon faced a backlash. Barack Obama’s election sparked a strong oppositional force from the right that included rejection of new legislative efforts on greenhouse gases. This response was in part a function of fervent advocacy by fossil fuel interests, but it soon blossomed into a central part of the conservative worldview. Addressing climate change was presented as an intrusion on capitalism that was trying to fix something that wasn’t an issue … or, later, that wasn’t an issue the United States alone could fix.

Activists had already been agitating for another way to curtail greenhouse gas emissions: having the EPA use its power to regulate pollutants to create rules that would limit the release of carbon dioxide. The EPA declined to do so in 1999, pushing the fight to the courts. After years of back-and-forth, the case got to the Supreme Court. In its 2007 ruling in Massachusetts v. EPA, the court (led by its liberal faction) determined that the EPA could use its Clean Air Act authority to regulate carbon dioxide and other…