Janet Yellen planted a flag during her confirmation hearing in January 2021. Climate change, she declared, was an ¡°existential threat,¡± and as U.S. Treasury secretary, she would make it a focus of her work.

Since taking office, she¡¯s warned of the danger to the economy and financial system. She¡¯s urged Congress and foreign governments in the rich world to do more to help poorer countries adapt to global warming, and thrown the Treasury behind implementing U.S. President Joe Biden¡¯s signature climate bill, seeking to squeeze the most from the sprawling new law.

Yellen is the ¡°best ally of climate action in the entire Biden administration,¡± according to Democratic Sen. Sheldon Whitehouse of Rhode Island, an outspoken climate hawk.