Negotiators from 200 countries are meeting in Poland for talks on curbing climate change. The crucial talks are happening three years after sealing a landmark deal in Paris that set a goal of keeping global warming well below 2 degrees Celsius. Climate scientists are calling this a “make or break” moment for the world. The meeting received a boost over the weekend, after 19 major economies at the G-20 summit affirmed their commitment to the 2015 Paris climate accord. The only holdout was the United States.