In the wake of Donald Trump's unexpected election to the presidency, climate experts are scrambling to recalculate whether the world has any chance of reaching the goals of the Paris climate accord if the president-elect makes good on his threat to withdraw from the deal.
One thing is for certain: The complex pact to limit global warming to less than two degrees Celsius will live on. Even if the United States pulls out, enough other countries have ratified the agreement to trigger its entry into force. And many experts say they don't expect the rest of the world to slack off on aggressive climate action simply because of the U.S. election.
If the U.S. rededicates its energy mix to fossil fuels, some other countries would look to step into the breach to try and take advantage of the growing worldwide demand for clean energy.
"If the U.S. decides not to embark on a low-carbon pathway, it will drag behind other major economies that will be eager to consolidate a dominant market share as producers of renewable energy technologies," says Joeri Rogelj, a carbon budget analyst with the International Institute for Applied Systems Analysis in Vienna, Austria. "It will be countries like China who will benefit from the U.S. running in the opposite direction and who will competitively outclass the U.S. economy."
Theoretically, it's possible that other countries could ramp up their efforts to cut greenhouse gas emissions to compensate for a lack of U.S. reductions, but that doesn't appear realistic, according to Louise Jeffery, an emissions expert with the Potsdam Institute for Climate Impact Research.
"I can't see a situation in which other countries make up the shortfall, for political reasons, as it would undermine the political basis of the agreement," Jeffery says. And without big U.S. emissions cuts, the climate math doesn't add up. "I would be surprised if it's possible to meet 1.5 to two-degree Celsius target without the U.S. meeting their commitment, at least if they don't reduce emissions from now until 2030," she says.
But even if the rest of the world presses ahead with emissions cuts, U.S. withdrawal would make it much harder for the signatories to meet the agreement's financial goals, including big funding targets to help developing countries pay for climate adaptation.
"On a more positive note, there are some things that Trump doesn't have so much control over, such as state legislation in California, or economic competitiveness of renewables, that could lead to mitigation in the absence of direction from the president," Jeffery says.
National Aeronautics and Space Administration climate researcher Gavin Schmidt says U.S. emissions are expected to decline during the next presidential term even under a Trump presidency, "because most of the efforts are at the state, city, and community level. Similarly, actions undertaken by Environmental Protection Agency that survive judicial review are very hard to change on a whim."
"Thus, while it's true that we probably can't expect much in the way of constructive leadership from Washington (as usual), action will continue," he says. "This is a long game, not a one-off. However, note that existing pledges are insufficient in any case to stabilize CO2 emissions, and that emission cuts need to be sustained well beyond a single election cycle to be successful. Thus, efforts need to be robust to the vagaries of the democratic process — and, frankly, most of them are."
Since the election result was unexpected, climate analysts haven't figured out exactly by how much other countries would have to cut emissions to compensate for lack of U.S. action, or even if it's practically doable.
"The remaining carbon budget for keeping warming to below 1.5 degrees Celsius or two degrees Celsius is very small, and staying within this budget requires declining global emissions rapidly and as soon as possible," Rogelj says.
In these first weeks after the election, it may not yet be possible to say for certain if the world can still meet the Paris climate targets.
"If emissions keep rising, obviously we're not going to keep warming to 1.5 degrees Celsius or two degrees Celsius, and to no other temperature level," Rogelj says. "However, the U.S. pledge for 2025 is particularly important to prepare nationally for the profound transition toward very low emission levels that is required afterwards, until mid-century."
According to calculations by Climate Analytics, a Berlin-based think tank, U.S. emissions in 2025 would be about 1 percent higher than the 2014 level if Trump dumps the Clean Power Plan, excluding land use change and forestry emissions.
"If the incoming Trump administration were to scrap the Clean Power Plan, it would mean that other countries would need to reduce their emissions by an additional 0.9 to 1.3 gigatons of CO2 to cover the gap that would be left," Climate Analytics CEO Bill Hare says. "This would represent 7 to 12 percent of the projected global 2025 emissions gap between the world's Nationally Determined Contributions and a two-degrees Celsius pathway," he says.
While some experts still see a narrow path to capping global warming somewhere below the catastrophic level, climate scientist Michael Mann has a bleak outlook.
"I'm afraid that our worst fears … have been been realized. A Trump presidency might be game over for the climate. It might make it impossible to stabilize planetary warming below dangerous levels," he says. "If Trump makes good on his campaign promises and pulls out of the Paris Treaty, it is difficult to see a path forward to keeping warming below dangerous levels. Hopefully the world will find a way to move forward in combating climate change even if the U.S. refuses to play an active role."
As perhaps a last-ditch effort to get a new administration on-board with international climate action efforts, a few experts agree the best way forward might be to appeal to Trump's business sense.
"I would argue that a transition to renewable energy also provides an important economic and political opportunity for the U.S. to tackle some of the concerns regarding jobs," Rogelj says. "A distinct shift to renewable energies can create the jobs that are currently lacking in depreciated areas of the U.S. It is to be seen which choice the U.S. will make in this regard."
Corinne Le Quéré, director of Tyndall Centre for Climate Change Research at the University of East Anglia, has a similar view, saying that costly and growing climate change effects to the U.S. economy from floods, droughts, and wildfires might cause Trump to choose a different view from what he's expressed in the past.
"The election of Trump could bring a new dimension to how we address climate change, if he so chooses," Le Quéré says. "Trump is a businessman. The biggest leap forward we could make to address climate change is to develop the business economy that will produce energy without the carbon, and there are huge opportunities for this in America, for example through their leadership in the Silicon Valley, from transforming the car industry to developing a cleaner energy grid and storage, bioenergy, and the circular economy."
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