On this Earth Day, world leaders gather at the United Nations to sign a landmark climate agreement. But is it enough? NY1's Vivian Lee reports from the U.N.

It's not every day more than 165 nations agree on something.

On this Earth Day, at the United Nations, they officially did, ratifying the Paris Agreement to slow global warming, the most states ever signing an international accord on one day. 

"As a global community, we are going to address the irrefutable reality that nature is changing at an increasingly rapid pace due to our own choices," U.S. Secretary of State John Kerry said.

The agreement's primary goal: curbing greenhouse gas emissions to limit the warming of the planet to 3.6 degrees, or 2 degrees Celsius. 

Actor and environmental activist Leonardo DiCaprio attended the ceremony and congratulated delegates.

"No more ten-year studies," DiCaprio said. "No more allowing the fossil fuel companies to manipulate and dictate the science and policies that affect our future."

But there already are concerns that the climate agreement, which was negotiated in Paris, does not go far enough.

The first three months of 2016 have broken temperature records, and 2015 was the warmest year since record-keeping began in the 19th century.

Some New Yorkers are worried the Paris Agreement falls short. Others said world leaders had to start somewhere.

"I think it's wonderful. I think it's much needed change that's happening," one woman said.

"I think it's a good start, but it's not far enough," one man said.

Mayor Bill de Blasio also spoke, hours after City Hall announced new rules for one million buildings to control their greenhouse gas emissions.