"Paris and Pittsburgh share the same environment after all," said NASA astronaut Scott Kelly.
French President Emmanuel Macron was also highly critical of Trump's decision. "Climate change is one of the major issues of our time," he said. "It is already changing our daily lives but it is global. Everyone is impacted."
"Wherever we live, whoever we are, we all share the same responsibility: make our planet great again," he said, echoing Trump's campaign slogan.
David Mack is a deputy director of breaking news for BuzzFeed News and is based in New York.