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Representatives of 195 nations agreed on Saturday to a landmark climate deal requiring each nation to significantly lower its greenhouse gas emissions as part of an urgent international effort to stave off the worst consequences of climate change.

The agreement is the culmination of two intense weeks of negotiations between delegates from every corner of the globe, who gathered in a huge tent-city compound on the outskirts of Paris to iron out the countless details involved in one of the most complex international climate deals ever attempted.

The United Nations conference on climate change, or COP21 (Conference of Parties), as it's called, which ended Saturday, follows nearly 20 years of largely failed efforts to forge a meaningful international agreement to lower GHGs. The Paris talks were considered by many world leaders, including President Obama, the last, best chance to prevent global temperatures from rising to catastrophic levels.

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The goal: to stop global average surface temperatures from rising above 2 degrees Celsius (about 3.6 degrees Fahrenheit) above pre-Industrial Revolution temperatures (when we started burning significant amounts of fossil fuel in the late 1800s). Temperatures rising above that 2 degree threshold, according to broad scientific consensus, would likely result in irreversible, catastrophic environmental consequences around the world, including rapid sea level rise and devastating flooding and drought.

But to keep global average temperatures a bay, each of the nations participating in the negotiations -- who are collectively responsible for almost 98 percent of global emissions -- have to dramatically reduce their own greenhouse gas (GHG) emissions (including carbon dioxide, nitrous oxide and methane). And that's a tricky proposition, because some countries have been emitting GHGs for decades, even centuries, and reaping huge economic benefits, while many other "developing nations" are just beginning that process. The deal, therefore, not only requires rich countries to significantly cut their emissions, it also mandates that they pay poorer countries to also cut emissions and adapt to the impacts of a changing climate.

But as the New York Times notes:

"The new deal will not, on its own, solve global warming. At best, scientists who have analyzed it say, it will cut global greenhouse gas emissions by about half what is necessary to stave off an increase in atmospheric temperatures of 2 degrees Celsius, or 3.6 degrees Fahrenheit. That is the point at which scientific studies have concluded the world will be locked into a future of devastating consequences, including rising sea levels, severe droughts and flooding, widespread food and water shortages, and more destructive storms."

The deal has also come under fire by some environmental activist groups who argue it's too weak to effectively prevent environmental disaster. They deal, they note is largely voluntary, lacking the necessary legally binding emissions reduction requirements.

Indeed, there are few firm mechanisms -- or consequences -- to ensure that each of 195 nations make good on their promises.

More than 180 participating countries have already submitted their specific carbon reduction pledges, called Intended Nationally Determined Contribution (INDC). Although signatories are legally required to meet every five years -- beginning in 2020 -- with updated emissions goals, the goals themselves are not legally binding. And because these emissions targets fall short of preventing catastrophic temperature rise, the agreement includes a process intended to ensure that countries will continue to strengthen their goals as renewable energy technology becomes more accessible.

The U.S. has promised to reduce GHG emissions by 26 to 28 percent of 2005 levels by 2025. And for ratification here, it requires only the signature of President Obama, rather than the approval of the U.S. Congress (where the majority of Republicans oppose it).

Although the U.S. pledge is more ambitious than some large carbon emitting nations like Russia, it pales in comparison to many other developed countries, including the 28 European Union nations, who have all committed to at least a 40 percent GHG reduction below 1990 levels by 2030.

Explore these interactive visualizations (above and below) to see all the countries making a pledge, who the world's biggest GHG emitters are and how much each nation is willing to cut back to reach that 2-degree goal. All data was compiled by the WRI. Click here for methodology.

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MAP: This Is How Much Each Country Is Pledging to Reduce Its Carbon Emissions