Abrupt climate change is a specific type of climate change that can occur naturally or possibly as a result of human activities. In abrupt climate change, the climate system changes to a new climate state rapidly, generally over a time scale which is much faster than the typical time scale of the climate forcing responsible for the change. Essentially, abrupt climate change is any sudden change in the climate system which results in a new climate state much more suddenly than is expected for whatever mechanism is responsible for the change. Abrupt climate change is often surprising (non-linear), hard on living systems (which could include people), and almost impossible to reverse. Many experts fear that anthropogenic climate change could become abrupt climate change, dramatically impacting people all over the world in bad ways.
Although external forcings can result in abrupt climate change, not all abrupt climate changes are externally forced. Some of these changes may be unexpected, and occur as the result of some strong, rapidly changing forcing that pushes the climate system in a nonlinear fashion. Abrupt climate changes can impact a region, hemisphere, or even the entire globe. One major concern with the climate change that is currently occurring as a result of human activities is that the changes that are occurring at a steady rate now could rapidly and suddenly change the climate system of the Earth. This case is concerning as there is not a good way to predict this sudden climate change, as well as the fact that adapting to some sudden change in the overall climate of a region would be extremely difficult.
There are several different ways that a drastic, abrupt change in the climate could occur. From observations of paleoclimatic records, there are four major types of changes that if they were to occur, they would pose significant risks in terms of how well society would be able to adapt to said changes. Essentially, if human activities are pushing the climate towards some sort of abrupt change, it is the following changes that would pose the biggest threat to humanity:
Other possible changes include:
One common notion that exists surrounding climate change is that climate is always changing, so any change happening currently is no different than natural climate shifts over time. However, the changes occurring in the climate presently are more accelerated than previous climate change events. This comparatively rapid increase in global surface temperature and changes in weather patterns can be seen as abrupt in comparison to historical events. For more information on how the climate is changing rapidly as a result of human effects, please see the IPCC's summary here or watch the video from 'This is not cool with Peter Sinclair' by Yale Climate Connections: