LE BOURGET, FRANCE—A historic, global agreement to combat climate change has been adopted here outside Paris. Aided by the submission of 186 national plans to cut greenhouse gas pollution, negotiators from 196 countries large and small, rich and poor united to deliver a new climate deal that may change the world or, in the words of the agreement's preamble "Mother Earth" (also known as land, seas, skies and life on this planet.)

The new Paris Agreement declares an ambition to hold global average temperature rise to 1.5 degree Celsius if possible, calls for greenhouse gas pollution to be balanced with greenhouse gas removals after 2050, implements a 5-year cycle of reviews of national plans and actions starting soon as well as monitoring of those actions, and confirms at least $100 billion per year to help those countries most affected by climate changes. It also calls for scientists to weigh in on how exactly the world might aim for 1.5 degree C given that temperatures are already up 1 degree C in 2015—the hottest year on record. Global greenhouse gas pollution must peak "as soon as possible," the pact states. The first official global "stocktake" of efforts to meet all these ambitions of the Paris Pact will occur in 2023.

The process of getting to the agreement has been both fraught and, somehow, smooth. French diplomacy has overseen the most organized international climate talks ever with stakes high, all overseen by foreign minister Laurent Fabius, though it took intense huddles of negotiators and frantic meetings in overheated plywood rooms well into the night of December 12 to deliver a final deal at 7:29 PM Paris time. "We worked a great deal, we didn't sleep a lot," Fabius says. Real issues have had to be worked out, especially money, monitoring and motivation to achieve more in terms of greenhouse gas reductions. For example, debate raged over how to word the ultimate aim: below 2 degrees C, well below 2 degrees C or even below 1.5 degree C, before settling on "holding the increase in the global average temperature to well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 degree C." Now, this Paris pact could become reality once 55 nations, representing at least 55 percent of global greenhouse gas pollution, accept it.

Of course, the 186 national plans already submitted come nowhere near reaching the 1.5 degree or even 2 degrees C overarching goal of the Paris pact. Instead, national plans would result in global emissions of 55 billion metric tons of greenhouse gases in 2030, compared to roughly 35 billion metric tons today. An analysis of 146 of the submitted plans by the United Nations Framework Convention on Climate Change, which range from preserving forests in Indonesia to cutting coal in the U.S., suggests they could keep global warming to less than 3.7 degrees Celsius, if fully implemented by 2030. Hence the emphasis by the so-called "High Ambition Coalition" of countries on including 1.5 degree Celsius in the final deal, according to Tony de Brum, former foreign minister of the Marshall Islands. That amount of global warming—almost guaranteed given current concentrations of CO2 in the atmosphere—is meant to signal a willingness to strive to save countries facing existential risks from climate change. De Brum spoke of his grandchildren afraid of the sea despite growing up alongside the ocean, as high tides reach higher and higher. "That cannot be real, we have to fight that," de Brum says.

Another such country is the Pacific island nation of Tuvalu, whose Prime Minister, Enele Sopoanga, was keen on achieving not just money for adaptation but also for the damage already being experienced by his country, and expected to continue in future. "Loss and damage is for when you have nothing left to adapt to, when you have to move people off the islands," Sopoanga says. "My walkaway is the 1.5 limit."

That 1.5 C limit is reflected in the final agreement, and would require global greenhouse gas pollution to peak in 2020 and zero carbon by 2050 according to physicist Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research. The U.N. Intergovernmental Panel on Climate Change has been explicitly asked in the prelude to the Paris Agreement to develop its own comprehensive analysis of what it would take to hold global warming to 1.5 degree C, as well as what the impacts of that level of warming might be, by 2018. Though that goal may not be achievable, it also may spur and accelerate the shift to clean energy, better farming practices and the like. "I think we are all converted and we are all singing one song," Sopoanga says. "We need to sing that song louder."

The numbers do not add up, as of yet, but five-year cycles that require countries to ensure "progression" on national actions to combat climate change may help with that, as will a review, aimed at aiding laggard countries and enhancing the ambitions of ambitious ones, in 2018. In fact, after Paris, the world will start a "new process," says Gao Feng, a special representative on climate change from China's Ministry of Foreign Affairs. "We will develop all the necessary rules to make the Paris agreement operational."

"It's not the system we envisaged at the beginning but it's probably the best you can get," adds former biologist Alf Wills, now head of South Africa's negotiating delegation, in part because of obstacles like Republican politicians in the U.S. At the same time, those obstacles are preventing the U.S. from committing to a truly legally-binding agreement as well as more money for adaptation, damages and other impacts from climate change. "The U.S. is saying: 'You're going to take on more. We're going to take on less.' That's a hard pill to swallow."

Yet the nations of the UNFCCC have swallowed that pill, in part because of the bottom-up approach brought to the table by China. The so-called INDCs, or intended nationally determined contributions, enabled the deal to get done, as did prior agreements to curb greenhouse gases between major polluters like the U.S. and China.

In an impassioned late night plea as negotiations continued, U.S. Secretary of State John Kerry called the Paris pact a "monument to differentiation," as each country would be able to set its own goals thanks to these INDCs. "It has 186 completely voluntary, totally nationally determined plans," Kerry said in a closed door meeting to try to hash out a deal on December 10. "No two plans are the same. That's differentiation."

But the plans do have some common elements, such as shifting away from fossil fuels to cleaner energy, whether wind, solar, geothermal, nuclear or dams, as well as technology to capture the pollution associated with the cement and steel required to build those clean energy sources. They also include plans to protect existing forests and perhaps plant more, as well as changing farming practices to store more carbon in soil. And it means helping pay for this transition in countries, whether India or Zambia, that cannot afford such action on their own, as well as building up the capacity to act and adapt to the impacts of climate change. It also means acting in accordance with "the best available science," according to the Paris pact.

Yet zero carbon or an agreement to phase out fossil fuels are not directly mentioned in the Paris pact, replaced by the phrase "a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases," due to objections from fossil fuel economies like Saudi Arabia and Malaysia.

Saudi Arabia has been the most public blocker here on such long term goals but, as the saying goes, trees can hide the forest. The problems go much deeper than one oil-rich nation. For example, China's 4 billion metric ton per year coal habit poses a major challenge to world where greenhouse gas emissions are balanced by greenhouse gas reductions. "Humankind missed 16 years for taking action" prior to Paris, says Liu Zhenmin, vice minister of foreign affairs for China. "Our contribution has been very ambitious but I think our national conditions mean we will still have some difficulties to accomplish that contribution."

The direction is clear, however: move toward a low pollution civilization as quickly as possible, depending on national circumstances. That includes efforts like the deal struck between China and the U.S. to develop long-term, low emission strategies to restrain global warming—and share them widely. "The goal is to develop a low cost, low carbon energy system that can underpin the job growth and economic prosperity all areas of the world want to see," says John McArthur, a senior fellow in global economy and development for the Brookings Institution, a public policy research outfit in Washington, D.C.

In other words, the question after Paris is how to deliver clean energy and reduce greenhouse gas pollution to restrain global warming. As China's Gao adds: "This Paris outcome will lead the whole global community to a low carbon future."