The Critical Zone

Abrupt Climate Change


Those of us fortunate enough to have experienced Earth sciences in primary and secondary school probably learned about gradual climate change through geologic time, such as the gradual waxing and waning of continental-scale ice sheets during the last ice age. This view of paleoclimate change is appropriate in the context of Earth history and geologic time. However, more recently, paleoclimatologists have gathered evidence for widespread abrupt changes in climate that occurred in the not-too-distant past, on time-scales equivalent to a human lifetime. For those who are attentive to these issues, this realization has served as a "wake-up call" to action—humanity's effect on atmospheric composition and climate change may push the climate system toward a "tipping point" from which rapid regional and global changes in climate of unknown magnitude and duration may occur. The question remains whether human action to reduce greenhouse gas emissions can avert such events.

Reading assignment

Read the following text chapter:

  • Committee on Abrupt Climate Change & National Research Council. (2002). Evidence of Abrupt Climate Change. In Abrupt Climate Change: Inevitable Surprises (pp. 19–72). National Academies Press.

The first few pages of the chapter provide a brief overview of paleoclimate proxy interpretations, information you should now be familiar with and therefore can skip here if you choose. Pay particular attention to the discussion of the Younger Dryas, the most recent widespread episode of abrupt climate change for which abundant, globally distributed terrestrial and marine data has been collected.

  • How much temperature change occurred during the Younger Dryas, how was it distributed regionally, and over what time frame did it occur?
  • As importantly, how would a similar change in climate during your lifetime affect your lifestyle, and the lives of others in your region, in North America, and on Earth?

The concepts and terminology through this portion of the chapter should mostly be familiar to you.

When you reach the sections entitled "Patterns of Climate Variability" and "Trends Recorded Instrumentally," you may find that the terminology is unfamiliar—do not fret. Your primary focus through this portion of the chapter should be to understand that human records of recent-past climate change do exist and provide evidence for and are relevant to our understanding of ongoing and future climate change. Also, read the final section entitled "Synopsis of Observations."