For decades, Bill Gates has warned of climate disaster — but his tone meaningfully shifted as he cautioned against taking a "doomsday view" on the planet's future.

Bill Gates is calling for a change in the fight against climate change by shifting the focus away from reducing carbon emissions to fighting poverty and preventing disease and hunger.

“There is no reason to pit poverty reduction versus climate transformation,” Columbia University Center for Sustainable Development director Jeffrey Sachs told CNN, calling the memo “pointless, vague,...