— Ch. 1 · Defining Abrupt Transitions —
Abrupt climate change.
~5 min read · Ch. 1 of 6
The climate system can be forced to transition at a rate determined by its own energy balance. This transition occurs more rapidly than the change in external forcing, though it may include sudden events like meteorite impacts. Scientists define abrupt climate change through physics or through impacts. In terms of physics, it is a shift into a different mode on a time scale faster than the responsible forcing. In terms of impacts, an abrupt change happens so quickly that human or natural systems struggle to adapt. These definitions complement each other. The physical definition explains how such changes occur. The impact definition explains why researchers devote so much attention to them. Past examples include the end of the Carboniferous Rainforest Collapse and the Younger Dryas period. Some scientists use different timescales when discussing these events. For instance, the onset of the Paleocene, Eocene Thermal Maximum might have lasted anywhere from a few decades to several thousand years.
Geological Timescales
Changes recorded in Greenland ice cores imply a sudden warming within a timescale of just a few years. Other abrupt shifts include a temperature rise on Greenland 11,270 years ago. A separate event brought abrupt warming to Antarctica 22,000 years ago. By contrast, the Paleocene, Eocene Thermal Maximum initiated over a span ranging from decades to thousands of years. Earth System models project that under ongoing greenhouse gas emissions, near surface temperatures could depart from the usual range as early as 2047. This departure would happen within the last 150 years of variability. The Younger Dryas event began 12,800 years ago and moved back into a warm-and-wet climate regime about 11,600 years ago. It is the most recent of the Dansgaard, Oeschger cycles. These rapid changes suggest responses to thresholds or triggers in the North Atlantic climate system. A model based on disruption to thermohaline circulation has been supported by other studies.