activists are able to use the CAA as a means to combat GHG emissions in order to fight the acceleration of climate change. In 2009 the state of California was able to use the CAA to create stronger vehicle emission standards than the national standard, which quickly led to the Obama administration adopting these stricter emission standards on a national level. These standards were called the Corporate Average Fuel Efficiency (CAFE) standards and included regulations of GHGs. Massachusetts v. EPA One of the first landmark climate change litigation cases was Massachusetts v. Environmental Protection Agency, decided by the Supreme Court of the United States in 2007. The suit was brought by several American states against the Environmental Protection Agency (EPA) after the EPA declined to regulate carbon dioxide and other greenhouse gas emissions as part of their duty under the Clean Air Act (CAA) in 2003. The EPA had argued that their authority under the Clean Air Act were to regulate "air pollutants", which they claimed carbon dioxide and other greenhouse gases did not fall under, so could not apply regulations. States, like Massachusetts, argued that these emissions could lead to climate change-related damages to their states, such as through rising ocean levels, and thus these emissions should be seen as harmful under the CAA and within the EPA's ability to regulate. While EPA initially won at the Court of Appeals, the Supreme Court, on a 5–4 decision, agreed with the states that carbon dioxide and other greenhouse gases had been shown to be harmful, and required the EPA to regulate them. Juliana v. United States In 2015, a number of American youth, represented by Our Children's Trust, filed a lawsuit against the United States government in 2015, contending that their future lives would be harmed due to the government's inactivity towards mitigating climate change. While similar suits had been filed and dismissed by the courts for numerous reasons, Juliana v. United States gained traction when a District Judge Ann Aiken ruled that the case had merit to continue, and that "a climate system capable of sustaining human life" was a fundamental right under the United States Constitution. The United States government has since attempted to dismiss the case through various challenges to Aiken's findings, but it remains pending in court actions. European Court of Human Rights In September 2019, a group of six children and young adults from Portugal