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It was a bumper week for transatlantic goodwill. On Wednesday, at the elegant house of the French ambassador in Washington, French Foreign Minister Jean-Yves Le Drian and U.S. Secretary of State Antony Blinken commemorated Bastille Day, France’s national holiday. They unveiled what’s been dubbed the “little sister” of New York’s Statue of Liberty in the gardens of the residence, and Le Drian hailed “the new transatlantic momentum” forged by the Biden administration and its allies in Western Europe.

The next day, President Biden hosted German Chancellor Angela Merkel at the White House for a diplomatic swan song in Washington as her long spell in power draws to a close. The two leaders touted a new “Washington Declaration,” outlining a common political vision on democratic principles, human rights and an open world. “I’ll miss seeing you at our summits,” Biden told Merkel during a joint news conference.

It’s obvious that Europe’s political elites are relieved by the change in atmosphere that Biden represents after the disruptive tirades and tariffs of his predecessor. But they are wary of the possible return of Trumpist politics in the years to come. And even with Biden and his liberal internationalist lieutenants in power, plenty of wrinkles remain in Washington’s relations with its closest partners. Some will be difficult to iron out — including differences in strategy over China, Russia, trade and the regulation of Big Tech companies.

And then there’s the dangerous matter of climate change. The Biden administration has spent its first months in office rallying allies and partners to the cause of global climate action after the hiatus of the Trump years. Biden and his transatlantic colleagues, including Merkel on Thursday, tout their shared commitments to the struggle against climate change. But Europe is racing ahead with measures that could, in theory, provoke friction with the United States.

On Wednesday, the European Commission announced an ambitious set of plans that would put the bloc’s 27 member states on the path toward carbon neutrality by 2050. The legislative package includes proposals to tax jet fuel, ban the sale of gasoline- and diesel-powered vehicles in the next two decades, increase the use of renewable energy and raise funds to help lower-income households as national economies accelerate their transition off fossil fuels.

The most politically loaded element in the package could be “the creation of a ‘carbon border adjustment mechanism,’ which would impose tariffs on some goods imported from non-E.U. countries with weaker climate laws,” my colleagues reported. “In practice, environmental groups hope, this could become a powerful incentive for other nations to follow the bloc’s policies.”

In conversation with European Union officials, the Biden administration pushed against this proposed carbon tax on imports. If implemented, it could trigger a significant set of disputes between Brussels and Washington. “The White House could take a page from Trump’s trade playbook and impose its own retaliatory tariffs, or it could seek to challenge the EU’s move by resurrecting the World Trade Organization’s hobbled dispute resolution body, an option sharply opposed by U.S. climate policy advocates,” noted Politico.

“To the United States, I would say if you are so worried, then maybe it is time you come forward with very credible plans on decarbonization of your economy,” Bas Eickhout, a European lawmaker from a Dutch green party, told my colleagues. “We have heard a lot of announcements, but we have not seen many concrete policies.”

There’s no guarantee that the E.U. proposals will stick. The legislation would require approval from the bloc’s 27 member states and the European Parliament, and resistance is expected, especially from countries like Poland that are more reliant on fossil fuels.

Critics say measures like the carbon border tax illustrate how unpopular climate action may prove to be. “The climate tariff is a tacit admission that Western elites haven’t convinced their voters to pay the price of their climate obsessions,” noted the conservative editorial board of the Wall Street Journal. “In the process they’ll force their consumers to pay more for imports and domestic goods, and they’ll harm their own exporters if countries retaliate.”

“There are concerns that the poor will pay an inequitable share of the cost of decarbonization and that it will be seen as an elite project, prompting more political backlash from populist parties and groups, like the 2018 ‘yellow vest’ protests over a climate-related increase in French gasoline prices,” noted the New York Times.

“We have to do the [green transition] in such a way that all income levels can maintain their lifestyles,” Mark Rutte, the center-right Dutch prime minister, said earlier this year. “If we run up costs because of plans drawn up in Brussels or The Hague, we will lose support for what we are doing. It is crucial we carry society along.”

The E.U. plan’s supporters argue that the proposed measures would ultimately offset the steeper costs of transitioning away from fossil fuels, while working to meet the pledges made by governments to limit emissions. The Biden administration faces a similar political debate in Washington as it tries to push through a major $3.5 trillion spending bill that includes a number of climate-focused proposals.

Climate scientists and activists say inaction is not an option. “The fear of ‘more costs’ still seems to prevail, which of course ignores the already large costs inflicted today by climate change on taxpayers through increasingly violent extreme events,” Flavio Lehner, a climate scientist at Cornell University, said in an email.

The deadly heat wave that blazed through a vast stretch of North America this summer, which left hundreds of people dead and killed off as many as 1 billion sea creatures, is yet another sign of what’s to come. In the White House, Merkel pointed to the torrential rains this week that caused deadly floods in Germany and other parts of Western Europe as a “catastrophe” that ought to spur greater action.

“The last few weeks across the globe were a taste of this,” Lehner added. “Without aggressive climate mitigation, these extremes will continue to increase in frequency and severity, with increasing costs for individuals and governments alike.”

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