Jeff Bezos, the world's richest man, will spend $10 billion to combat climate change. He announced the news in an Instagram post on Monday.

"Climate change is the biggest threat to our planet," Bezos writes. "I want to work alongside others both to amplify known ways and to explore new ways of fighting the devastating impact of climate change on this planet we all share."

Bezos says that his new Bezos Earth Fund will fund "scientists, activists, NGOs—any effort that offers a real possibility to help preserve and protect the natural world." He says he'll begin issuing grants in the summer.

"We can save Earth," Bezos wrote. But "it’s going to take collective action from big companies, small companies, nation-states, global organizations, and individuals."

Bezos' Instagram post is light on details. He doesn't specify any time frame for his $10 billion pledge, so we don't know if he's planning to give that much in a year or over decades. And we don't know what kind of projects Bezos is looking to fund—though with $10 billion, Bezos could fund many different kinds of projects.

The new announcement follows growing pressure from some of Bezos's own Amazon employees. For months, some employees have been organizing inside Amazon to push the company toward more climate-friendly policies. That pressure may have contributed to Amazon's September decision to order 100,000 electric trucks and aim for net-zero carbon emissions by 2040.

Last month, activist employees defied an Amazon policy prohibiting employees from commenting on Amazon's business practices without permission from Amazon management. Hundreds of rebellious employees called on Amazon to do more to fight climate change, including cutting off business with oil and gas companies that use Amazon's cloud-computing services.