Our changing climate

This chapter summarizes how climate is changing, why it is changing, and what is projected for the future. While the focus is on changes in the United States, the need to provide context requires a broader geographical perspective in some parts of the discussion. Additional geographic detail is presented in the regional chapters of this report. Since the previous national climate assessment was published in 2009, the climate has continued to change, with resulting effects on the U.S. The trends described in the 2009 report have continued, and our understanding of the data and ability to model the many facets of the climate system have increased substantially. Several noteworthy advances are mentioned in the chapter.