The Paris climate agreement seeks to keep the global average rise in temperatures below 2C, but until it’s ratified, it will achieve nothing. Saturday, the deal came one step closer to coming into force legally after China and the U.S, who together are responsible for 40 percent of the world’s carbon emissions, formally joined the Paris global climate agreement. This is big because it can only come into place after it’s ratified by at least 55 countries, which between them produce 55 percent of global carbon emissions. Before China made its announcement, only 23 nations accounting for just over 1 percent of emissions had ratified the agreement. Now it’s time for other major nations to do the same.