The election of Donald Trump -- and his vow to once again undertake a US retreat from international climate diplomacy -- poses a decisive threat to the fight against global warming as the window for meaningful action closes.
Mr Trump's win comes just days before representatives from nearly 200 nations gather in Azerbaijan for COP29, the annual United Nations climate summit. That two-week meeting will start on Monday in the shadow of a Republican president-elect who has promised to lead another withdrawal from the landmark 2015 Paris Agreement.
Mr Trump's victory is "an alarming escalation of climate risk for the world's most vulnerable communities", said Harjeet Singh, a climate activist for the Fossil Fuel Non-Proliferation Treaty Initiative. "By stepping back from climate commitments, Mr Trump's actions threaten to unravel trust in a global system already strained by the indifference and inaction of wealthy nations."
Diplomats are already wrestling with the consequences. Although Mr Trump won't be sworn in for two months, his election turns the US delegation to COP29 into lame ducks with diminished credibility and less leverage. It's also likely to constrain countries' ambitions in setting new carbon-cutting pledges due next February.
Beyond the fallout at COP29, there could be far more sweeping consequences. Another US retreat from climate cooperation has the potential to obliterate any lingering hope of keeping the world's temperature rise below 1.5C, a critical goal enshrined in the Paris Agreement.
"We need dramatically raised global ambition to have any chance of staying below 2 -- much less 1.5 -- degrees," said Alden Meyer, a senior adviser with the climate change think tank E3G. The US reversal has "a real world impact," he said.
The US has long been viewed as both an unreliable and necessary partner in annual climate talks. The country failed to ratify the Kyoto Protocol that underpins the negotiations more than two decades ago, and it has partially reneged on its past pledge to steer billions of dollars to a UN climate fund.
Back in 2017, this lack of dependability culminated in then-President Trump's announcement that he was pulling out of the Paris Agreement. Even though other countries didn't follow the US withdrawal and President Joe Biden was able to rejoin the agreement in 2021, the exit still sidelined a country that's been essential to driving momentum on climate action. The US is the largest shareholder of the World Bank, a key institution for financing the energy transition, and American negotiations with China have helped forge bilateral consensus, spur action in Beijing and pave the way for watershed global commitments, including a 2023 agreement to transition away from fossil fuels.
The US also has wielded its diplomatic might -- and leveraged its existing relationships with other nations -- to secure bigger international climate agreements and deeper emission-cutting pledges. It's "a pretty powerful diplomacy machine", said Jake Schmidt, senior strategic director of international climate at the Natural Resources Defence Council. "Having the US not driving that diplomacy will definitely hurt the push to get more finance and more action."
Climate finance negotiations in Azerbaijan "will be the earliest test of the resilience of the climate regime", said Li Shuo, director of the Asia Society Policy Institute.
Mr Trump's ascension could shift the balance of power to other countries and blocs, strengthening the role for the European Union in landing a deal. It could also intensify pressure on the EU to reach an agreement with China, which is being pressured to join the group of wealthy nations contributing to annual climate finance targets.
"If you are the EU" faced with the Trump victory, "you understand we have one less traditional donor," Mr Li said. "You could be more interested in getting China" into the fold.
Still, the EU itself is entering this year's negotiations on the backfoot, with several of its top leaders skipping the conference to deal with political issues at home. German Chancellor Olaf Scholz has cancelled his trip to Baku after calling a snap election, according to a person familiar with his plans, while European Commission President Ursula von der Leyen and French President Emmanuel Macron will also be absent.
Some countries are expected to unite in a joint statement committing to climate action in the wake of the US election, mirroring their response when Mr Trump's 2016 win unsettled UN talks in Morocco.
Environmentalists, government leaders and former negotiators have spent months plotting ways to Trump-proof global cooperation. That kind of coordination didn't happen last time when Mr Trump's first win caught so many global leaders by surprise.
Actions taken in the private sector and at lower levels of government can help fill some of the US emission-cutting gap, but it's no substitute for a robust federal government push. Under the Paris Agreement, the US had pledged to slash its greenhouse gas emissions at least 50% by 2030 from 2005 levels. Even with existing federal policies -- including regulations Mr Trump has already vowed to terminate once in the White House -- the US still needed to do more to fulfil its 2030 commitment, according to projections from the research firm Rhodium Group.
Environmentalists are now worried that other countries may respond to a US retreat by dialling back their own carbon-cutting promises. The effects could be most pronounced for laggard nations and big fossil fuel producers. It may be a long shot, but some activists also see this as an opportunity to prove climate action doesn't hinge on any single nation. Bloomberg
Jennifer Dlouhy reports for Bloomberg News.