So it's done, the bang of a gavel Saturday night signaled that representatives of almost 200 nations have reached a landmark agreement to lower greenhouse gas emissions and fight climate change.

The historic breakthrough that involved both rich and poor countries – whereas such pacts traditionally required action only from developed economies – committed to keeping global temperatures from rising another 1 degree Celsius (1.8 Fahrenheit) from now to 2100.

Loud applause and embracing and some weeping among delegates ensued after French foreign minister Laurent Fabius gaveled the agreement, which United Nations diplomats had been working to realize for nine years now.

“History will remember this day,” U.N. secretary general Ban Ki-moon said, dubbing the Paris climate change agreement a “monumental success for the planet and its people.”

U.S. President Barack Obama spoke from Washington and lauded the climate agreement: “[It is] the best chance to save the one planet we have.”

In the climate change agreement, countries pledge to limit their greenhouse gas emissions from human activity to the levels that can naturally be absorbed by trees, soil, and oceans, starting between 2050 and 2100. The goal is to keep the global temperature rise by 2100 compared with pre-industrial times below 2 degrees Celsius (3.6 Fahrenheit), and even aim to limit it even more to 1.5 degrees Celsius.

Earth has already warmed by around 1 degree Celsius since the pre-industrial period.

Before taking effect, the deal needs to be ratified by at least 55 countries making up at least 55 percent of global emissions.

A number of challenges hounded the climate deal, including the final language used. Poorer nations, for instance, pushed for a legally binding provision that requires richer nations to employ at least $100 billion annually to help them adapt to and mitigate climate change effects.

In the final Paris agreement, the said $100 billion appeared in the preamble alone, not in the pact’s legally binding section.

The success of the climate accord is now believed to rely on global peer pressure as well as the next move of future governments. Notably, however, countries are required to create a plan but there is no stated legal requirement on how or how much they should cut emissions.

Countries are also required to reconvene every five years beginning 2020 to update their emission cut missions.

The Obama government, through behind-the-scene negotiations by Secretary of State John Kerry to help broker the agreement, forged a deal with China in 2014 to work together and scale back their emissions as the world’s two leading greenhouse gas producers. Some environmental groups said the accord reflected commitment from large nations.

“This is a pivotal moment where nations stepped across political fault lines to collectively face down climate change,” said World Wide Fund vice-president of climate change Lou Leonard.

Some, however, blasted Obama’s office for not pursuing greater ambition in the treaty.

Eric Pica, U.S. chapter president of environmental group Friends of the Earth, argued that the U.S. has hindered ambition. “The result is an agreement that could see low-lying islands and coastlines swallowed up by the sea, and many African lands ravaged by drought.”

Others remained hopeful like Climate Central sea level researcher Ben Strauss, who counted on limiting warming to 1.5 degrees as a way to slash in half the expected 280 million people worldwide whose houses will be submerged by rising seas.

Greenhouse gases mostly come from the burning of oil, gas, and coal for energy – cutting emissions of which is now a shared endeavor of at least 196 countries, whether rich or poor.

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