Our reporter hits the treadmill to understand how scientists study extreme heat.

© Christopher Capozziello for The New York Times

A Trump appointee has proposed rewriting a measure that requires companies to clean up “forever chemicals,” documents show. The new version would shift costs from polluters.

Hidden River Cave was once filled with heavy metals and sewage that made the surrounding town smell awful. After a cleanup, it became a tourist draw.

© Jason Gulley for The New York Times

Countries failed to bridge wide gaps on whether the world should limit plastic manufacturing and restrict the use of harmful plastic chemicals.

© Ariana Drehsler for The New York Times