April 23, 2021 1:28 PM EDT

Last year, as the COVID-19 pandemic raged, leaders around the world pledged that when the public health crisis lifted they would rebuild the economy with climate in mind. But as the pandemic dragged on, so too did any expectation that we might know whether leaders had actually stepped up to meet the challenge.

Now, after months of fits and starts, this week’s White House climate summit marks the beginning of what is sure to be a long slog for countries to deliver on those promises. “This summit is our first step on the road we’ll travel together,” Biden said on Thursday, alluding to the series of summits and conferences that will culminate in the landmark UN Climate Change conference scheduled for November, “to set our world on a path to a secure, prosperous, and sustainable future.”

Over the course of the day on Thursday and Friday, dozens of government heads from across the globe promised aggressive action on climate change, from commitments to slash emissions to promises to help developing countries finance their domestic energy transition. Whether they deliver remains to be seen.

Bringing the world together for a U.S.-led climate summit was always going to be an uphill battle. Biden first proposed the idea on the campaign trail, seemingly to remind voters of his experience on the world stage and his familiarity with foreign leaders. And, when he was elected, most of the people who work on international climate issues didn’t have a clue what shape it would take. Not only would the Biden Administration need to contend with planning a summit in the midst of a pandemic, but the U.S. would need to shake off four years of climate denial from the Trump Administration and convince the world that a U.S.-led climate summit was worth attending.

Biden got to work immediately. During his transition, he selected former Secretary of State John Kerry to serve as his climate envoy, a choice whose familiar face would open doors from Beijing to Brussels. And, upon taking office, Biden signed a flurry of climate executive orders and promised to infuse the issue to everything the administration does—a signal to the world that the U.S. might lead once again.

Over the past several months, Kerry has hopped around the world. He visited Europe in March before Antony Blinken had left the country as Secretary of State and then, a few weeks later, he made the first to visit China from a senior Biden official. “What we’ve agreed to do in each of those instances is to work at specific efforts,” Kerry told me after returning from Europe last month, citing partnerships with France and the United Kingdom on finance as two examples. Kerry’s visit to China yielded a joint statement saying the two countries are “firmly committed to working together.”

When the summit finally rolled around in April, a handful of countries were ready to announce new climate targets. Canada upped its commitment to slash emissions to at least a 40% reduction from 2005 levels by 2030. Japan said it would aim for a 50% cut from 2013 levels by the end of the decade. The most important commitment, of course, came from the U.S.: the Biden Administration said the country would reduce its greenhouse gas emissions by at least 50% by 2030 from 2005 levels, a significant ramp up from the U.S.’s Obama-era plan.

Still, the world has a long way to go. A new analysis released Friday morning by Climate Action Tracker suggests that since September countries have narrowed the gap between emissions cuts needed to keep warming to 1.5°C by the end of the century and committed emissions cuts by up to 14%. That’s significant, but leaves much work to be done to keep the 1.5°C target—an approximate level at which the world may begin to see some of the most catastrophic results of warming.

The Biden summit’s success or failure can’t be measured simply by looking at those targets. In part, the summit is an opportunity to make the case to the world—including those skeptical of the U.S.—that the U.S. now understands the seriousness of the challenge and is putting it at the top of the agenda. Officials announced a slew of new initiatives and programs to show the administration’s resolve. The summit included everyone from the Secretary of Defense to the Secretary of Commerce to discuss how they were incorporating climate into their agendas. The administration also placed business leaders and local government squarely in the fold, clearly indicating the expectation that this year’s climate discussions will require more than just national governments.

Diplomatically, the biggest achievement may simply be getting everyone to show up in the midst of a global health crisis. Forty heads of government were invited; all accepted. Even leaders known for the foot dragging on climate change—think of Brazil’s Jair Bolsonaro and Russia’s Vladimir Putin—came with positive statements. Officials hope this will set the stage for discussions set to carry out over the course of the year.

Whether those and other statements mean anything will become clear in the months to come. The summit is just one moment on a crowded calendar designed to build momentum for the UN climate conference in Glasgow in November, the first major UN climate conference in six years. In the year leading up to the last major conference, which yielded the landmark Paris Agreement, the U.S. negotiated a series of bilateral agreements that helped build momentum and convince the world the country could be taken seriously. This year, too, leaders will try to build momentum with a series of meetings. In the coming months, leaders will focus on climate at the Petersberg Climate Dialogue hosted by German Chancellor Angela Merkel, the G7 Summit hosted by the U.K. and the G20 summit hosted by Italy—among many others.

If these efforts succeed, it will be just in time. Just a few days before the summit began, the International Energy Agency (IEA) reported that the recovery from COVID-19 is fueling a rapid ramp up in carbon pollution. Emissions are expected to increase by 5% this year after falling a record 5.8% last year, according to the IEA. And coal—the most carbon intensive fossil fuel—is playing a big role in that rise. Meanwhile, the planet has already warned as much as 1.2°C—inching slowly but surely to the 1.5°C mark. “The science is very clear that we can still reach 1.5 degrees,” says Jennifer Morgan, the head of Greenpeace International. “But clearly time is running out.”

On the cover of TIME in July, I wrote that this moment—2020 and 2021—represented our “last, best chance” to avoid catastrophic levels of warming. The discussions that take place between now and November between nations, the private sector and regional and local governments will determine whether we meet the moment. “Glasgow remains our last best hope,” Kerry told reporters at the White House on Thursday, “to coalesce the world in the right direction.”

Write to Justin Worland at justin.worland@time.com.

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