State Department diplomat Tom Shannon, long slated to take the helm of the U.S. delegation at the United Nations climate summit in Bonn, won’t be coming due to a family emergency, the State Department said Nov. 14, adding a new complication to talks intended to begin implementing the Paris climate pact.

Ordinarily, that job of top U.S. negotiator at the U.N. summit would fall to Trigg Talley, a longtime State Department climate negotiator tasked with leading U.S. climate diplomats until Shannon’s arrival to take the reins in Bonn for the final three days of the Nov. 6–17 summit. But Talley departed the German city early Nov. 14 for his own family emergency, according to several members of the U.S. delegation.

Shannon will be replaced by Judith Garber, the acting assistant secretary of state for oceans, environment, and science, the State Department said. Garber is a longtime career diplomat and was tapped in September to lead the U.S. delegation to Geneva for the first conference of the parties to the global treaty to limit mercury use, formally known as the Minamata Convention on Mercury.

Signs of Division

The announcement came amid signs of division between career State Department negotiators, who are largely focused on procedures to implement the Paris climate pact, and Trump administration political appointees sent to the Bonn summit, who are arguing that fossil fuels can play a role in helping to meet global climate goals.

One obvious result of the reshuffling is the substitution of a lower level State Department official in Garber—who is in an acting capacity—for Shannon, the third-ranking diplomat at the State Department. It’s also unclear which U.S. representative will address a high-level plenary at the Bonn talks Nov. 15, where world leaders and environment ministers are to speak and where Shannon was slated to deliver remarks on behalf of the U.S.

The moves come at a tricky time in the negotiations, which are already complicated by President Trump’s announcement in June that he will pull the U.S. out of the 2015 Paris climate deal, according to Alden Meyer, who tracks the talks for the Union of Concerned Scientists.

The two-week summit is coming down to its final three days, Meyer said, with focus on key “politically charged issues” such as climate finance, loss and damage suffered by poorer nations more vulnerable to climate change, and any additional actions countries might take before 2020 to curb their emissions.

“This is a whole level of complexity she’s stepping into to lead the U.S.” as the talks come down to the wire, Meyer said of Garber, the new delegation head.