Bill Gates is as optimistic about the world’s future as ever, despite the fact that we’re living through “an era with so many challenges and so much polarization,” the billionaire philanthropist and Microsoft co-founder wrote in a blog post on Friday.

The world faces plenty of causes for concern over issues like climate change, global health and poverty, and disruptions caused by artificial intelligence, Gates wrote. However, “we are far better off than when I was born 70 years ago,” wrote Gates, due particularly to innovations in technology and global health.

Gates also believes that conditions will keep improving over the next two decades, especially as AI spurs new advances, he wrote: “I am still an optimist because I see what innovation accelerated by artificial intelligence will bring.”

But there are a few caveats. “These days, my optimism comes with footnotes,” wrote Gates.

Specifically, Gates is concerned about three questions that could determine “the trajectory of [the world’s] progress,” he wrote: