She cited the International Energy Agency’s findings that no new gas or oil fields should be developed to reach net-zero emissions by the middle of the century and stay within relatively safe levels of global warming. Shell last year put forward a net-zero strategy but still plans to explore new fossil fuel projects until 2025, and recently started campaigning for the U.K. government to let the company develop a new North Sea gas field.

“It pains me to end this working relationship which I have greatly valued, but I can no longer work for a company that ignores all the alarms and dismisses the risks of climate change and ecological collapse,” Dennett wrote.