US officially back in the Paris climate agreement

The United States officially rejoined the Paris climate agreement on Friday, reinvigorating the global fight against climate change as the Biden administration plans drastic emissions cuts over the next three decades.

Scientists and foreign diplomats have welcomed the US return to the treaty. 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.

US climate envoy John Kerry will take part in virtual events on Friday to mark the US re-entry, including appearances with the ambassadors to the UK and Italy, UN secretary gGeneral Antonio Guterres and UN climate ambition envoy Michael Bloomberg. Biden has promised to chart a path toward net-zero US emissions by 2050.

Scientists have said that goal is in line with what is needed, while also stressing that global emission 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," US 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 22 April. The next UN climate conference is in November in Glasgow.

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

Despite the excitement over the US 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 US 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.