At noon on December 12th - 12 o'clock on 12/12 - the bells of Notre Dame were tolling non-stop, as the electronic notification went out that international climate negotiators had released a final agreement. The two things were completely unrelated, but it was a memorable moment, nonetheless.
About mid-way through the second week of climate talks in Paris, a draft agreement came out that surprised a lot of people. Instead of sticking with the long-standing goal of limiting warming to 2 degrees Celsius above pre-industrial levels, negotiators adopted an agreement that sets the target "well below 2°C" and calls for "efforts to limit the temperature increase to 1.5 °C."
That sent scientists and policy experts scrambling to predict just what it would take to reach that goal. Johan Rockstrom of Stockholm University suggested that developed nations would need to shut off the lights on the Monday after the talks to reach the goal, while Ajay Gambhir of the Grantham Institute at Imperial College, London, said the world has five to ten years before we need to bring carbon emissions to zero. The truth is, though, that researchers haven't put together solid scenarios for stopping warming at 1.5 °C, because that goal has never been on the table before.
And the agreement isn't as ambitious as either of those scenarios. It calls for greenhouse gas neutrality by the second half of this century. However, it also provides an important mechanism for reassessing progress and setting new (more ambitious) emisisons reduction plans every five years.
Here in the U.S., implementing the agreement is possible as long as the actions remain within the Clean Air Act. The Supreme Court has upheld the EPA's ability to regulate carbon dioxide and other greenhouse gases. Experts say the next U.S. president can't just abandon the agreement, because it carries the weight of a treaty despite the lack of approval by Congress.