This article from Nature, which is really a plea to maintain and increase funding for ocean current research (and in my view a worthwhile plea to make), touches on an interesting dilemma. One impact of rising temperatures, at least in the northern hemisphere, is the dumping of enormous amounts of icy meltwater into the Atlantic from the Arctic and Greenland. This water sinks to the deep ocean, but if enough pours into the Atlantic it can push aside the warm Gulf Stream, push it south, weaken its flow. This, in turn, means that Europe is not warmed, and this in turn means that snow doesn’t melt, forming the basis for the growth of ice sheets. And, whether the weakening of the Gulf Stream flow started at the end of the Little Ice Age in 1850 when the earth warmed, as one model suggests, or started in the mid 1900s due to human impacts, as another model suggests, the outcome is the same – a future of cold, not warmth. And, it seems, a future that might fall upon us very rapidly, once it happens.