US officially rejoins the Paris Agreement on climate change

The United States has officially rejoined the Paris Agreement, which focuses on climate change mitigation and adaptation, on Friday, a move that scientists and foreign diplomats have welcomed. The U.S. had withdrawn from the Paris accords in 2017 under the Trump administration, a year after it had signed the agreement along with 195 other countries.

The return to the treaty became official 30 days after President Joe Biden ordered the move on his first day in office, reinvigorating the global fight against climate change as the Biden administration plans drastic emissions cuts over the next three decades.

Since nearly 200 countries signed the 2015 pact to prevent catastrophic climate change, the United States was the only country to exit. Former President Donald Trump took the step, claiming climate action would cost too much.

U.S. climate envoy John Kerry will take part in virtual events on Friday to mark the U.S. re-entry, including appearances with the ambassadors to the U.K. and Italy, U.N. Secretary General Antonio Guterres and U.N. climate ambition envoy Michael Bloomberg.

Biden has promised to chart a path toward net-zero U.S. emissions by 2050. Scientists have said that goal is in line with what is needed, while also stressing that global emissions need to drop by half by 2030 to prevent the most devastating impacts of global warming.

"Climate change and science diplomacy can never again be 'add-ons' in our foreign policy discussions," U.S. Secretary of State Antony Blinken said in a statement. "It is vital in our discussions of national security, migration, international health efforts, and in our economic diplomacy and trade talks."

Kerry along with Biden’s domestic climate adviser, Gina McCarthy, are crafting new regulations and incentives aimed at speeding the deployment of clean energy and transitioning from fossil fuels.

Those measures will form the backbone of Washington’s next emissions reduction goal, or Nationally Determined Contribution, to be announced before a global climate leaders summit Biden will host on April 22. The next U.N. climate conference is in November in Glasgow.

Biden also has also signed more than a dozen executive orders related to climate change, and has mobilized every federal agency to help shape the government's response.

Despite the excitement over the U.S. return to global negotiations, climate negotiators say the path forward will not be easy. Biden’s climate goals face political challenges in the United States, opposition from fossil fuel companies and some concern among foreign leaders about U.S. flip-flopping on climate policy.

"There’s a lot of ground to make up, but the hope of Paris is alive and strong," said Rachel Cleetus, policy director at the Union of Concerned Scientists.