The Trump administration notified the international community Monday that it plans to officially withdraw from the Paris climate accord next fall, a move that will leave the world’s second-largest emitter of greenhouse gases as the only nation to abandon the global effort to combat climate change.

President Trump has long criticized the 2015 accord and insisted that the United States would exit it as soon as possible. As recently as last month, Trump called the agreement “a total disaster” and argued that the Obama administration’s pledges to cut carbon emissions under the deal would have “hurt the competitiveness” of the United States.

In a statement Monday afternoon, Secretary of State Mike Pompeo said the administration had sent official notification of its plans to the United Nations.

“In international climate discussions, we will continue to offer a realistic and pragmatic model — backed by a record of real world results — showing innovation and open markets lead to greater prosperity, fewer emissions, and more secure sources of energy,” Pompeo said. “We will continue to work with our global partners to enhance resilience to the impacts of climate change and prepare for and respond to natural disasters.”

Environmental and public health activists quickly condemned the decision, even as it came as no surprise.

“Abandoning the Paris agreement is cruel to future generations, leaving the world less safe and productive,” Andrew Steer, president of the World Resources Institute, said in a statement. “It also fails people in the United States, who will lose out on clean energy jobs, as other nations grab the competitive and technological advantages that the low-carbon future offers.”

The Paris climate agreement legally entered into force Nov. 4, 2016, after the United States and other countries formally joined the landmark deal. Under rules set out by the United Nations, no country could leave the accord for three years, after which there is a one-year waiting period for the withdrawal to fully take effect.

Monday marked the first day that the Trump administration could give that one-year notice, and it wasted no time. That means the United States can now officially leave the Paris agreement Nov. 4, 2020 — the day after next year’s presidential election.

Should a Democrat win the White House, the nation could reenter the agreement after a short absence — as numerous candidates have pledged. But if Trump prevails, his reelection would probably cement the long-term withdrawal of the United States, which was a key force in helping forge the global effort under President Barack Obama.

Monday’s move comes as scientists say that the world must take “unprecedented” action to cut its carbon emissions over the next decade, slashing them in half by 2030 to avoid irreversible and potentially catastrophic effects of climate change.

The world already has warmed more than about one degree Celsius (1.8 degrees Fahrenheit) above preindustrial levels. The Paris agreement set ambitious goals to keep the planet’s warming “well below” a rise of two degrees Celsius (3.6 degrees Fahrenheit) and if possible, not above 1.5 degrees Celsius (2.7 degrees Fahrenheit).

A Washington Post analysis has found, however, that roughly one-tenth of the globe has already warmed by more than two degrees Celsius, when the past five years are compared with the mid- to late 1800s.

Monday’s action also comes only weeks after world leaders gathered at the U.N. Climate Action Summit in New York as part of a push to encourage nations to make high-profile commitments to cut the emissions that fuel global warming. That event laid bare the tensions between a growing activist movement eager for more aggressive action and global leaders who have yet to commit to the transformational changes that scientists say are essential to averting the worst effects of climate change in coming decades.

“The biggest cost is doing nothing,” U.N. Secretary-General António Guterres told the gathering. “The biggest cost is subsidizing a dying fossil fuel industry, building more and more coal power plants and denying what is plain as day — that we are in a deep climate hole, and to get out, we must first stop digging.”

In a Rose Garden appearance June 1, 2017, Trump first announced plans to withdraw the nation from the Paris agreement, under which nearly 200 countries had made voluntary, nonbinding pledges to reduce their carbon emissions over time. He argued that the accord “disadvantages the United States to the exclusive benefit of other countries.”

Critics have called Trump’s dismissal of the Paris accord irresponsible and dangerous, given the increasingly dire scientific warnings about rising sea levels, more-extreme weather and devastating effects on agriculture and wildlife should the world fail to drastically cut its greenhouse gas emissions. They also call the decision bad economic policy, saying the administration is failing to embrace wind, solar and other renewable technologies that are growing, even as the coal industry that Trump has tried to bolster continues to fade.

“While the world will not be surprised, it’s a sad reminder of where the world’s former leader on climate change now stands,” Susan Biniaz, a lecturer at Yale Law School and former State Department climate negotiator, said in an email about Monday’s announcement. “The decision of two years ago [to abandon the Paris accord] is now even more grotesque — the reasons for withdrawing are no more correct, and the science is even clearer that, far from withdrawing, we should be increasing our efforts.”

A growing number of Americans describe climate change as a crisis, and two-thirds say Trump is doing too little to tackle the problem, according to a recent poll conducted by The Post and the Kaiser Family Foundation.

The poll found that a large majority of Americans — about 8 in 10 — say that human activity is fueling climate change, and about half believe action is urgently needed within the next decade if humanity is to avert its worst effects. Nearly 4 in 10 now say climate change is a “crisis,” up from less than a quarter five years ago.

While Democratic lawmakers and presidential candidates joined environmental groups in blasting Trump’s decision on Monday, the withdrawal won praise from some conservative corners.

“Free market innovation — not crippling global agreements — will help reduce global carbon emissions and address climate change,” Sen. John Barrasso (R-Wyo.), who in 2017 was among nearly two dozen GOP senators who had urged Trump to ditch the Paris accord, said in a statement.

Even as world leaders have promised to forge ahead on climate action without the United States, progress has been slow and uneven.

The emissions-cutting pledges that countries unveiled in Paris were nowhere near sufficient to meet the goals detailed under the agreement — a reality world leaders have repeatedly acknowledged. The plan was for nations to ramp up their ambition over time. And while dozens of countries have signaled their intentions to do that over the coming year, it remains unclear whether it will be nearly enough to put the world on a more sustainable trajectory.

Global emissions of carbon dioxide reached record-high levels in 2018, scientists said late last year, underscoring the gap between the world’s aspirations for combating climate change and what countries are actually doing.

Meanwhile, the Trump administration has continued to aggressively roll back Obama-era environmental rules aimed at reducing carbon emissions, including regulations intended to accelerate the shift away from coal-fired power plants and steadily increase the fuel efficiency of the nation’s auto fleet.

And the president has made clear that he views increasing fossil fuel production — not renewable energy and international climate agreements — as the more important priority for the nation.

“I feel that the United States has tremendous wealth. The wealth is under its feet. I’ve made that wealth come alive,” Trump said during a news conference this summer in France. “I’m not going to lose that wealth — I’m not going to lose it on dreams, on windmills.”

Carol Morello contributed to this report.