U.S. climate envoy John Kerry is leaving, the Biden administration announced over the weekend, which leaves climate policy up in the air.

What we're watching: U.S. climate relations with China. Kerry's longtime Chinese counterpart, Xie Zhenhua, just retired. So there's big change on both sides.

Why it matters: China and the U.S. are the world's two largest emitters of carbon dioxide.

One big question: Whether the two nations do — or don't — breathe life into a November 2023 agreement to bolster joint work on methane curbs and other areas.

What they're saying: "As John Kerry moves on, the biggest champion for cooperation with China on climate leaves government. The future of U.S.-China climate diplomacy will look very different," Joseph Majkut of the Center for Strategic and International Studies posted on X.

The U.S. succession plan isn't clear. The White House and State Department did not provide comment on who will replace Kerry.

State of play: President Biden could seek another high-profile name for the role. But Kerry also has seasoned lieutenants in Sue Biniaz and Rick Duke.

• Bloomberg reports potential successors include Washington State Gov. Jay Inslee, and John Podesta, a top White House energy aide who has climate diplomacy experience.
• The intrigue: A new law since Kerry got the job requires Senate confirmation for many special envoys — a huge hurdle for any Biden pick. That could apply to a new climate diplomat, depending on how the job is structured.

The bottom line: Kerry wants to help Biden politically. Keep an eye on how the former Massachusetts senator may be deployed in the 2024 campaign to sell the president's climate policies.