Climate scientists have long warned that the Earth's climate system contains a number of so-called tipping points — thresholds (0) BEYOND which changes become irreversible and self-sustaining. The melting of the Arctic ice sheet, 1 instance, illustrates this phenomenon clearly. As ice melts, it exposes darker ocean water beneath, which absorbs more heat and causes further melting in what amounts 2 a vicious cycle. What makes tipping points so dangerous is that, once crossed, there may be little that can be 3 to reverse the process, regardless of how aggressively emissions are subsequently reduced. Recent research suggests that some of these thresholds may have 4 been breached, though the full consequences will not become apparent for decades. This uncertainty is 5 makes the issue so difficult to communicate to the general public, many of 6 understandably struggle to grasp the scale of the threat. Sceptics have seized 7 this uncertainty to argue that the risks are being exaggerated, but the overwhelming consensus among scientists is that the danger is real and growing. The available evidence makes 8 abundantly clear that failing to act now would constitute a gamble of unprecedented proportions.