Paris (CNN)[Breaking news update, posted at 1:35 p.m. ET] The final draft of the climate change agreement reached in Paris was formally accepted at the 21st Conference of Parties, or COP21, on Saturday. After years of buildup and weeks of negotiations, diplomats issued a final draft of a climate change agreement Saturday that the French foreign minister described as "fair ... and legally binding." If adopted, the agreement would set an ambitious goal of halting average warming at no more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial temperatures -- and of striving for a limit of 1.5 degrees Celsius if possible. World leaders hailed the draft as a milestone in the battle to keep Earth a planet that is hospitable to human life. But there is still a mountain to climb. The draft now goes to government ministers. Delegates from 196 parties to the U.N. Framework Convention on Climate Change will be asked later in the day to adopt or reject the proposal. And different countries may well have ratification procedures back home. The Kyoto Protocol on reducing the emission of greenhouse gases was concluded in 1997. In the United States, the Clinton administration signed the agreement but, fearing defeat, never submitted it to the Senate for ratification. This time, political pressure for an agreement is coming from many quarters. In the streets of Paris, outside the conference, protesters demanded action. #ParisAgreement was trending on Twitter. "Nous sommes la nature qui se défend!" read one tweet, with a photo of one person dressed as a polar bear and another dressed as a penguin. "We are nature that defends itself." Some demonstrators felt differently -- they called the agreement insufficient and chanted "it's a crime against humanity." "We have a 1.5-degree wall to climb but the ladder isn't tall enough," Kumi Naidoo of Greenpeace said at a press conference. He did call the agreement a "new imperative" and positive step. Many in the scientific and environmental activist communities have responded with cautious optimism. "This didn't save the planet," Bill McKibben, the co-founder of 350.org, said of the agreement. "But it may have saved the chance of saving the planet." Said Jennifer Morgan, of the World Resources Institute: "If this [the Paris Agreement] is adopted as this currently stands then countries have united around a historic agreement that marks a turning point in the climate crisis." Those participating in the negotiations said the draft agreement was an enormous achievement. "Today we are close to the final outcome," said French Foreign Minister Laurent Fabius, the host of the talks. "It is my deep conviction we have come up with an ambitious and balanced agreement." Scientists and policy experts say that would require the world to move off fossil fuels between about 2050 and the end of the century. To reach the more ambitious 1.5 degrees Celsius goal, some researchers say the world will need to reach zero net carbon emissions sometime between about 2030 and 2050. Ban: 'We need all hands on deck' U.N. chief Ban Ki-moon hailed the draft that was put together at the 21st Conference of Parties, or COP21. "We must protect the planet that sustains us," Ban said. "For that we need all hands on deck." Capping the increase in global average temperatures to 2 degrees Celsius was organizers' key goal going into the COP21 That level of warming is measured as the average temperature increase since the Industrial Revolution. Failure to set a cap could result in superdroughts, deadlier heat waves, mass extinctions of plants and animals, megafloods and rising seas that could wipe some island countries off the map. The only way to reach the goal, scientists say, is to eliminate fossil fuels. Despite those dire predictions, getting all nations on board with the text of the draft was a monumental task. "It's time to come to an agreement" 'Nobody will get 100 percent of what they want "Obviously, nobody will get 100% of what they want," Fabius said Friday as he discussed the "balanced and as ambitious as possible" working document that will be voted on. "What I hope is that everyone remembers the message of the first day, when 150 heads of state and government came from all around the world to say, 'The world needs a success.'" After the decision in Paris, the countries that adopt the agreement will later have to ratify it nationally. Negotiators took a key step December 5 with the release of a draft agreement that has been posted online by the United Nations Framework Convention on Climate Change. That draft has been modified throughout the week. A ways to go Even though a draft is ready to be agreed upon, there's still much more that needs to be done before the agreement actually goes into effect. The treaty must be adopted by "consensus" during a meeting of government ministers set for Saturday afternoon in Paris. That doesn't necessarily mean all 196 parties need to approve it; it's the job of Fabius, who serves as the president of COP21 to decide if a consensus has been reached. If it's adopted, it then goes to individual countries for their own ratification or approval. The entire agreement enters into force once 55 countries (who must account for 55% of the total global greenhouse gas emissions) have ratified it. That means if the world's biggest polluters don't sign off on the agreement, enacting it could prove challenging. China and the United States, respectively, account for about 24% and 14% of total greenhouse gas emissions, according to the World Resources Institute. Two-thirds of the U.S. Senate must sign off on a treaty before it can be ratified. That could be difficult to do in a Republican-controlled Senate that counts climate change skeptics among its members (including the chairman of the Environment and Public Works Committee, Sen. James Inhofe) and has sought to block President Barack Obama's actions on climate change. In China, the Standing Committee of the National People's Congress is in charge of approving treaties. The agreement calls for a signature ceremony in April 2016, and requests that the U.N. Secretary-General keep the agreement open for signing until April 2017. An honor system? Many officials have talked about the importance of doing something to slow the pace of global climate change. Having legally binding reductions in greenhouse gas emissions has long been seen as a priority. The agreement doesn't mandate exactly how much each country must reduce its greenhouse gas emissions. Rather, it sets up a bottom-up system in which each country sets its own goal -- which the agreement calls a "nationally determined contribution" -- and then must explain how it plans to reach that objective. Those pledges must be increased over time, and starting in 2018 each country will have to submit new plans every five years. Many countries actually submitted their new plans before COP21 started last month -- but those pledges aren't enough to keep warming below the 2 degrees target. But the hope is that over time, countries will aim for more ambitious goals and ratchet up their commitments. Another sticking point has been coming up with a way to punish nations that don't do their part, but observers say that was never really on the table. Instead, the agreement calls for the creation of a committee of experts to "facilitate implementation" and "promote compliance" with the agreement, but it won't have the power to punish violators. Another issue, according to observers, was whether there would be reparations paid to countries that will see irreparable damage from climate change but have done almost nothing to cause it. The agreement calls for developed countries to raise at least $100 billion annually in order to assist developing countries. CNN'sDon Melvin, Ralph Ellis and Greg Botelho contributed to this report.