Biden promised to bring the United States back to the global leadership in the fight against climate change, but the task wasn't easy after Trump's term.

Joe Biden has named former Secretary of State John Kerry as top global climate policy officer and has a seat on the National Security Council of his future government.

Environmental activists, who hope the new administration will see climate change as a central issue, welcome this information, but this is a difficult task for both Kerry and Biden.

After 4 years of the presidency of President Donald Trump, America's reputation in the international arena has been seriously affected.

To end the Trump era and restore America's global leadership on climate, Biden and Kerry must accelerate policies to cut domestic emissions and support partners making progress in the field.

"We have to rejoin the field, as we engage with our allies in a humble spirit," said Gina McCarthy, former head of the US Environmental Protection Agency (EPA) and now president

Part of the Biden administration's strategy is to remind the world of what he has done in the past.

Kerry is not only famous around the world, but also has earned exceptional credibility in climate debate.

The first problem of the Biden administration is whether the US can do what it said and pursue climate policy that has far-reaching effects in the country.

However, climate policymakers around the world recognize the challenges the Biden administration will face when it comes to finding ways to pass bills in the bicameral parliament, as well as challenges from the system.

The most important thing to win back the trust of global leadership is likely to depend on the Voluntary National Commitment (NDC), a new US commitment to reduce emissions that will be announced next year.

Paris-signatories expect similar pledges to be made by the members on the eve of the conference, and a strong Biden administration's NDC will send the clear message that the US is back.

However, observers argue that things have to wait and see, when the US returns, how the US will shape discussions about the global climate.

Under the Obama era, climate change was seen as an "olive branch", where the US-China sector could cooperate in a constructive spirit, in the context of military and trade tensions between the two sides.

"You have to work with them," said Jonathan Pershing, the State Department's former climate change special envoy.

The US and China are the two largest gas emitters in the world, accounting for more than 40% of global emissions.

Observers say the outlook will be different in the EU, where member states will surely respond to the US leadership role.

"America really faces a massive decline in the credibility of its allies and the rest of the world," said Nat Keohane, vice president of the Environmental Protection Fund and former climate policy advisor to President Obama.

It is not clear what approach Biden will take to rebuild relationships and bridge these gaps.

"I will call for 100 or more countries, but 100 major emitters to come to the US in the first 100 days," Biden said during the March Democratic preliminary debate. "If they refuse, they will have to

International climate policy experts say Joe Biden is unlikely to choose such sanctions, partly because the US needs to focus on domestic action before it can threaten to punish others.

Many experts also expect the Biden administration to start next year by pursuing foreign policy rather than sanctions against other countries.

"We need an American return to drive a movement that has already begun," said Laurence Tubiana, president of the European Climate Organization who was a key member of the Paris Agreement as Ambassador of Change.