As delegates from more than 190 nations gather today in Glasgow, Scotland, for the opening of the United Nations climate summit known as COP26, they find themselves in a perilous situation largely of their own making. In the years since the signing of the historic Paris Agreement in 2015, the world was supposed to act decisively, putting humanity in a far better position climate-wise now than it was then. The planet’s largest economies — the U.S., China, India, U.K. and E.U., along with other nations — were to cut greenhouse gas emissions. The wealthiest countries were also to raise billions o…