Since the 1980s, the United States has faced a myriad of environmental challenges that have sparked debates over policies and legislation aimed at addressing these concerns. One significant movement has been the push for stricter regulations on emissions, highlighting a growing awareness of climate change. While the 1990 Clean Air Act Amendments aimed to mitigate air pollution, the mid-2000s saw renewed calls for policies that balance economic growth with sustainable practices. Which of the following pieces of legislation is considered a milestone in federal efforts to limit greenhouse gas emissions beginning in the early 21st century?