4 Things to Know About the Paris Climate Deal

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World leaders have reached a pivotal climate agreement in Paris, seen here from the International Space Station. (Photo: NASA)

The United Nations made history this weekend, striking an unprecedented deal to phase out the industrial carbon dioxide emissions that fuel global climate change.

Humbly named the Paris Agreement, the 32-page document might seem a little brief in light of its herculean task. But while it doesn't address everything — and some critics say it left out too much — its leanness belies how big of a deal it really is.

U.N. climate talks have a long history of disappointment, and the high-profile failure of a 2009 summit in Copenhagen left many people disillusioned with climate diplomacy in general. The Paris Agreement won't solve the problem quickly, or maybe at all, but it does provide realistic hope after decades of frustration.

"The Paris Agreement is a monumental triumph for people and our planet," U.N. Secretary-General Ban Ki-moon said in a speech announcing the deal shortly after it was adopted Saturday night. "It sets the stage for progress in ending poverty, strengthening peace and ensuring a life of dignity and opportunity for all.

"What was once unthinkable," he added, "has now become unstoppable."

So what makes the Paris Agreement different from previous climate pacts? What does it offer that the Kyoto Protocol didn't? The entire document is available online, but since it's written in the dense language of diplomats, here's a cheat sheet:

Earth's atmosphere
Earth's atmosphere now holds 400 ppm of CO2, more than ever before in human history. (Photo: NASA)

1. Two degrees of separation.

All countries at the Paris climate talks agreed on one key goal: "holding the increase in the global average temperature to well below 2°C above pre-industrial levels."

Staying below that limit won't stop climate change, which is already under way, but scientists think it can help us prevent the most catastrophic effects. Each country submitted a public pledge for cutting its CO2 emissions, known as "intended nationally determined contributions," or INDCs. So far, these INDCs don't put us on a path to meet the 2-degree goal, but the agreement includes a mechanism to "ratchet up" countries' CO2 cuts as time goes on (more on that below).

In addition, the delegates in Paris agreed "to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels."

Francois Hollande and Christiana Figueres
French President Francois Hollande hugs U.N. climate chief Christiana Figueres on Dec. 12, after envoys from 195 nations adopted the Paris Agreement on climate change. (Photo: Francois Guillot/AFP/Getty Images)

2. The more the merrier.

One big difference about the Paris Agreement is that 195 different countries agreed on it. Getting that many world leaders to agree on anything is a tall order, but the geopolitics of CO2 emissions make climate negotiations especially difficult.

The pact represents not just international solidarity, but nearly across-the-board acceptance of responsibility for climate change. That's a big leap from the Kyoto Protocol, which required cuts from some developed nations (due to their larger historical CO2 output) but not from developing nations, even China and India.

China alone accounts for more than 25 percent of global CO2 emissions, so it's key to any climate deal. The U.S. is No. 2 at about 15 percent, and the two have recently set aside their differences to create a new, friendlier mood that helped set the stage for success in Paris. Yet despite their outsized influence, this deal wouldn't work without the other 193 countries. France has been widely praised for its performance as host and mediator, for example, and India was far more cooperative than many had anticipated. Even the tiny Marshall Islands played a major role, leading a "high-ambition coalition" that successfully pushed for certain inclusions in the deal.

To address developing countries' smaller responsibility for existing CO2 pollution — which lingers in the atmosphere for centuries — some of the wealthiest countries have agreed to give poorer parts of the world $100 billion by 2020, to help with CO2 cuts as well as climate-adaptation plans. Some countries raised their offers during the Paris talks, with the largest financial pledges coming from Europe.

coal-fired power plant in Shanxi, China
After decades of runaway growth, China has pledged its CO2 emissions will peak in 2030. (Photo: Kevin Frayer/Getty Images)

3. It's legally binding — sort of.

One of the trickiest aspects of any climate deal is its legal authority in individual countries, and this time was no exception. The Paris Agreement ended up with a careful mix of voluntary and mandatory elements.

Most notably, the INDCs are not legally binding, so countries that miss their CO2 goals face no official consequences. The deal would obviously be stronger if they did, but given reservations held by key players in Paris (including the U.S. and China), it also might not have happened. This was done largely to accommodate the U.S. political environment, since legally binding CO2 cuts would have required Senate approval, which is widely considered impossible under current Republican leadership. But while the INDCs are voluntary, other parts of the deal are not.

Countries will be legally required to monitor and report their emissions data, for instance, using a standardized system. Delegates from all 195 countries must also reconvene in 2023 to publicly report their progress toward meeting their CO2 goals, something they'll then need to do again every five years. Since there's no legal pressure for countries to stay on track, the mandatory monitoring, verifying and reporting of CO2 data is meant to prod them with peer pressure instead.

Paris climate change protest
Climate protesters in Paris hold a banner reading "Let's be the change.". (Photo: Francois Guillot/AFP/Getty Images)

4. We've only just begun.

Since existing INDCs aren't enough to meet the U.N.'s 2-degree target, and even those are only voluntary, what hope is there for actually keeping Earth's temperature rise below 2 degrees? That's where the "ratchet mechanism" comes in.

The ratchet is being hailed as one of the biggest victories in the Paris Agreement. It requires countries to submit new pledges by 2020, detailing their emissions plans for 2025 to 2030. Some developing nations resisted this idea, pushing instead for a less ambitious timetable, but they eventually relented. So, depending how future ratcheting talks go, this deal could grow stronger with age.

The Paris Agreement is certainly historic, marking humanity's best, most coordinated effort so far to fight man-made climate change. But plenty of hurdles lie ahead, including a few more procedural steps. The document will soon be deposited at U.N. headquarters, where each country's ambassador can sign it starting in April. Then it will need to be ratified by at least 55 countries — representing at least 55 percent of global CO2 emissions — so it can take effect by 2020.

And even after that, it will depend on ongoing commitments from hundreds of world leaders not to break the peace made in Paris this month. While self-interest has often derailed previous efforts to unite the global community, the solidarity seen in Paris over the past two weeks suggests we may be entering a new era of climate policy.

"We have an agreement. It is a good agreement. You should all be proud," Ban told delegates Saturday. "Now we must stay united — and bring the same spirit to the crucial test of implementation. That work starts tomorrow."