We often think of some of the most grievous impacts of anthropogenic climate change, such as species extinction and shifts in ocean circulation, as unfolding over centuries. However, a recent report from the US National Research Council points out that such impacts have sometimes occurred over decades rather than centuries. The report assesses the probability of fourteen types of extreme impact occurring abruptly before the end of the century, and it finds a strong probability for two: mass extinctions and extreme droughts, floods, and storms. But uncertainty remains high. For example, the report judges the collapse of the West Antarctic Ice Sheet (with a 3 to 4 meter rise in ocean level) “plausible” but is unable to assign a probability. Given the number of possible impacts identified, at least one surprise seems likely by 2100, enough to justify significant effort to address the underlying cause: global warming.