Five years ago, representatives from nations around the world gathered in Paris and agreed to take drastic measures to curb climate change. For many, it was a moment of unity and hope. But underlying the Paris Agreement was the understanding that those ambitious plans would not actually achieve the agreed-upon international goal of limiting global warming to an increase of 1.5 degrees Celsius. That goal seemed even less attainable when the U.S., the world’s second largest greenhouse gas emitter after China, dropped out under President Donald Trump. Why We Wrote This Scientists agree that the emissions targets set by the Paris Agreement five years ago won’t rescue humanity from catastrophe. A virtual gathering on Saturday aimed to close the “ambition gap.”