What to Know Trump's decision to pull out of the Paris agreement deals a major blow to efforts to combat climate change

The president's announcement came the same day that a study was released that says climate change threatens many NYC neighborhoods

Hundreds took to the streets of NYC to protest and several buildings, including One World Trade Center, were lit green in solidarity

Hundreds of people protested in Lower Manhattan and buildings were lit green in solidarity after President Trump declared Thursday that the U.S. is withdrawing from the landmark Paris climate agreement.

Trump’s decision strikes a major blow to worldwide efforts to combat climate change and distances the U.S. from many allies. It also led to widespread condemnation, from social media to the streets of New York City.

About 400 protesters gathered at Foley Square after Trump’s announcement. They held signs and chanted, “What do we want? Climate justice! When do we want it? Now!”

The crowd marched through the streets to nearby City Hall, where they pounded drums and chanted, “You can’t drink oil, leave it in the soil!”

In a show of solidarity, Gov. Cuomo said One World Trade Center and the Kosciuszko Bridge would be lit green on Thursday night. Mayor de Blasio said City Hall would also light up green.

The World Trade Center, the Kosciuszko Bridge and City Hall went green Thursday night after President Trump said the U.S. would pull out of the Paris climate agreement. Hundreds of people protested in the city.

The U.S. Conference of Mayors said it strongly opposed the decision and said mayors will continue efforts to reduce greenhouse gas emissions blamed for global warming.

Under former President Obama, the U.S. had agreed under the accord to reduce polluting emissions by about 1.6 billion tons by 2025. But the targets were voluntary, meaning the U.S. and the nearly 200 other nations in the agreement could alter their commitments.

Framing his decision as "a reassertion of America's sovereignty," Trump said, "I was elected to represent the citizens of Pittsburgh, not Paris."

Trump said that he would begin negotiations to re-enter the agreement or establish "an entirely new transaction" to get a better deal for the U.S. But he suggested re-entry was hardly a priority. "If we can, great. If we can't, that's fine," he said.

Trump’s announcement came the same day that a study was released saying East Harlem is one of the most vulnerable neighborhoods to both flooding and poor water quality. Experts say if Sandy had hit during high tide, East Harlem would have been completely under water.

According to the study by the Waterfront Alliance, 400,000 New Yorkers face a 50 percent risk of major flooding over the next 40 years.

President Trump withdrew from the Paris climate accord on Thursday. Critics call it a major blow to efforts to combat climate change. How could climate change affect the New York City area? Ida Siegal reports.

“To think that a storm like that could affect this neighborhood is pretty scary —and not just the storm, but the long-term aftermath of that,” Christina Nadler, of East Harlem, said.

The neighborhoods most at risk are East Harlem and the Lower East Side in Manhattan; Mott Haven and Throggs Neck in the Bronx; Coney Island and Sheepshead Bay in Brooklyn; Howard Beach and the Rockaways in Queens; and Mid-Island on Staten Island.

The study’s authors say to make those neighborhoods safe barriers, like those planned for Staten Island, need to be built and the world needs to combat climate change.

“Stop pouring carbon into the atmosphere, stop the global warming,” Waterfront Alliance CEO Roland Lewis said.

Annette Fisher, of the Coney Island Beautification Project, had her home decimated during Sandy back in 2012. She still struggles to secure funding to rebuild.

“What about the people who weren’t here to speak today, who are going to become bankrupt and whose houses are going to be foreclosed on,” Fisher said. “We have to get Trump to wake up!”

By abandoning the world's chief effort to slow the tide of planetary warming, Trump was fulfilling a top campaign pledge. But he was also breaking from many of America's staunchest allies, who have expressed alarm about the decision. Several of his top aides have opposed the action, too, as has his daughter and adviser, Ivanka Trump.

Scientists say Earth is likely to reach more dangerous levels of warming sooner as a result of the president's decision because America contributes so much to rising temperatures. Calculations suggest withdrawal could result in emissions of up to 3 billion tons of additional carbon dioxide in the air a year — enough to melt ice sheets faster, raise seas higher and trigger more extreme weather.

Trump, however, argued the agreement had disadvantaged the U.S. "to the exclusive benefit of other countries," leaving American businesses and taxpayers to absorb the cost.