From the Executive Summary: "Human activities, particularly CO2 emissions from fossil fuel combustion, have driven atmospheric greenhouse gas (GHG) concentration levels higher than at any time in at least 800,000 years (IPCC 2013). As a result, the Earth has warmed at an alarming rate over the past century, with average temperatures increasing by more than 0.8°C (1.5°F). The consequences are already severe. Heat waves and droughts are more common, wildfire seasons are longer and fires larger and more costly, and extreme weather is becoming more intense and unpredictable. Left unchecked, from 2000 to 2100, global average temperature increases of 2 to 5°C (3.6 to 9°F) and sea level rise of two to four feet are likely, and much larger increases are possible. Climate change will reduce long-run economic growth and jeopardize national security. With the adoption of the Paris Agreement in December 2015, the world took a decisive step toward avoiding the most dangerous impacts of climate change. The Paris Agreement aims to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels. Consistent with this objective, Parties aim to balance GHG emissions sources and sinks in the second half of this century or, in effect, achieve net-zero global GHG emissions. Countries have submitted near-term targets to address GHG emissions, called 'nationally determined contributions' or NDCs, and will review and extend these targets every five years. The Paris Agreement further invited countries to develop by 2020 'mid-century, long-term low greenhouse gas emission development strategies.' This document answers that call, laying out a strategy to deeply decarbonize the U.S. economy by 2050."
United States White House: https://www.whitehouse.gov/