evidence: For the endnotes, please download the PDF version of this issue brief. Editors: Daniel Bresette, Carol Werner, and Anna McGinn Note: This issue brief was published in October 2019, but was updated in Spring 2022 to include more up-to-date information about the overall climate impact of aviation as well as the impact of the COVID-19 pandemic on commercial aviation recovery and growth. Previously, commercial aviation was thought to be responsible for approximately 5 percent of the world’s climate-warming problem. Newer research, using the metric "effective radiative forcing," concludes aviation accounted for 3.5 percent of total anthropogenic climate warming in 2011, and likely in 2018 as well. According to the Intergovernmental Panel on Climate Change (IPCC), effective radiative forcing is a more accurate metric than radiative forcing as it is "a better indicator of global mean temperature response." Scientists continue to acknowledge uncertainty in determining the influence of non-CO2 factors in aviation’s overall climate impact. The revision also reflects the United States’ adoption of ICAO’s carbon standard for commercial aviation aircraft in January 2021.