One of modern climate science’s pioneers is warning that the world isn’t just steadily warming but is dangerously accelerating, according to a study that some other scientists call a bit overheated. The work from former NASA top scientist James Hansen, who since leaving the space agency has become a prominent protester against the use of fossil fuels, which cause climate change, illustrates a recently surfaced division among scientists about whether global warming has kicked into a new and even more dangerous gear. Hansen, who alerted much of the United States to the harms of c...