The same day President Trump pulled out of the Paris Agreement, New York, California, and Washington announced the formation of the Alliance.
It aims to uphold United States commitments under the Paris Agreement, and to try and meet or exceed the Clean Power Plan, an Obama-era rule on power plant emissions.
As of last month, the Alliance had 15 members including Puerto Rico and now American Samoa has become a member.
The governor's executive order says that as a remote island territory American Samoa strongly believes in the power of alliances and partnerships to address complex issues such as climate change and so has joined the Climate Alliance.
The Governor's executive order also documents the territory's commitment to combat climate change by systematically reducing greenhouse gas emissions and improving resiliency to weather changes.
Photo: RNZI / Monica Miller Lolo Matalasi Moliga at his State of the Territory address.