This is an interesting paper indeed - a new PNAS paper argues that before an abrupt climate change, there is a characteristic SLOWING DOWN of climate change that might be a warning sign:
Putting our results in an even wider perspective, it is important that slowing down is a universal property of systems approaching a tipping point. This implies that our techniques might in principle be used to construct operational early warning systems for critical transitions in a wider range of complex systems where tipping points are suspected to exist, ranging from disease dynamics and physiology to social and ecological systems.
Well worth a read. Hat tip to Stuart Staniford for pointing it out.