Caroline Lucas: This debate could not be more important. The Arctic is on fire; 2020 is on course to be the hottest year on record; and 16 of the 17 hottest years on record have been since 2000. There is such a thing as being too late. This is a pivotal moment, because the actions that we take over the next few weeks and months will either lock us into high-carbon dependency for decades to come, in which...