Biden named former Secretary of State John Kerry to a new top position on global climate policy, a public step toward what the President-elect has promised will be a renaissance in American leadership on the issue.

Activists who hope climate change will play a central role in the new administration cheered the news, but both Kerry and Biden have their work cut out for them. After four years under Donald Trump, the Biden Administration inherits a badly bruised international reputation. Trump repeatedly denied the science of climate change, rolled back dozens of environmental and emissions-reduction regulations, and earned the derision of nearly 200 nations who co-signed the Paris Agreement on climate change when he announced the United States’s withdrawal from the pact six months after taking office.

With the U.S. retreat, the European Union and China came to occupy central leadership roles, while feeling burned by Washington — a pattern that has repeated itself over decades of climate discussions. “[The U.S.] been a little like Lucy pulling away the football from Charlie Brown and Peanuts,” says Alden Meyer, an independent strategist with four decades of experience in senior positions at major U.S. environmental groups. “The world has seen this movie too many times, and they’re getting tired of it.”

To turn the page on the Trump era and re-establish the U.S. as a global leader on climate, Biden and Kerry must rapidly accelerate emissions-reduction policies domestically and offer tangible support to partner nations that are making progress abroad. Crucially, allies say, the U.S. will need to reengage the world with a recognition that Washington can no longer unilaterally dictate the terms of engagement. “We have to reenter this field, when we join our allies, with a great sense of humility,” says Gina McCarthy, the former Environmental Protection Agency head who is now the president of the Natural Resources Defense Council. “We have a great deal of trust that we have to rebuild across the world.”

Part of the Biden Administration’s strategy will be to remind the world of the President-elect’s history of engagement. As a chair of the Senate Foreign Relations Committee and, later, during his eight years as Vice President, Biden developed a positive reputation on the international stage, helping to usher in a golden era of American climate diplomacy. Kerry is also not only well-known internationally, but enjoys particular credibility in climate discussions. As Obama’s Secretary of State, he helped broker deals to win over developing countries and ensure adoption of the Paris Agreement.

The first real test will be whether the U.S. can put its money where its mouth is and pursue sweeping climate policy at home. Biden’s commitment to use a “whole of government” approach to tackle climate change — incorporating it into policymaking in nearly every agency from the Treasury Department to the Department of Defense — represents an important start, allies say. Restoring the Obama-era regulations that Trump has nixed, from vehicle emissions standards to rules targeting methane emissions, will also be key. Still, climate policymakers around the world are aware of the difficulties the Administration will face passing legislation through a divided Congress, as well as the potential challenges posed by an increasingly conservative judiciary.