The question of whether the final agreement from Cop28 includes a call for a “phase-out” or “phase-down” of fossil fuels is seen by many as being the single most important indicator of success at the UN summit. The issue may appear to be a simple scientific one but is in fact complex and deeply political. A call for a phase-out of fossil fuels gives the strongest possible signal to the world that the burning of coal, oil and gas must be reduced rapidly to have a hope of keeping the global temperature rise below 1.5C. And that is why some...