Abrupt Global Climate Change

Some time ago we pondered the future of humanity in the context of changing global climate (Can—and Will—Mankind Survive). We came across suggestions that climate change can be calamitous not only on the long timescale, but also on short timescales. We had this quote from John Terborgh: "The earth maintains a stable environment because it is a dynamic system and dynamic systems possess stable equilibriums. Less widely recognized is that the earth is a complex dynamic system. A cardinal feature of complex dynamic systems is that they can attain multiple forms of equilibrium."

This quote describing a prediction by James Lovelock makes clear what the previous statement implies.
"In his latest book....he argues that Earth’s system of self-regulation is being overwhelmed by greenhouse gas pollution and that Earth will soon jump from its current cool, stable state into a dramatically hotter one. All climatologists acknowledge the existence of such climatic jumps—as occurred for example at the end of the last ice age....A new climatic jump, he concludes, will occur within the next few years or decades, and will involve an abrupt increase in average global surface temperature of 9 degrees Celsius—from 15 to 24 degrees Celsius (59 to 75 degrees Fahrenheit). Such a shift, he contends, will trigger the collapse of our global civilization and the near extinction of humanity."

Recall that current climate models predict major effects from just a few degrees Celsius change. Are these purely hypotheses, or is there any evidence for abrupt climate changes?

The American Institute of Physics (AIP) provides an excellent summary of how data and the beliefs of earth scientists have evolved over time. The answer provided to the above question is a definite "yes."

Scientists became ever cleverer and more precise in interrogating the earth to determine historical records of temperature changes.
"By the 20th century, scientists had rejected old tales of world catastrophe, and were convinced that global climate could change only gradually over many tens of thousands of years. But in the 1950s, a few scientists found evidence that some changes in the past had taken only a few thousand years. During the 1960s and 1970s other data, supported by new theories and new attitudes about human influences, reduced the time a change might require to hundreds of years. Many doubted that such a rapid shift could have befallen the planet as a whole. The 1980s and 1990s brought proof (chiefly from studies of ancient ice) that the global climate could indeed shift, radically and catastrophically, within a century — perhaps even within a decade."

A shocking moment came when two groups extracted ice cores from deep within Greenland’s ice field. The cores were taken from locations 30km apart and, arriving at the same results, confirmed each other’s surprising results.
"Ice core analysis by Dansgaard's group, confirmed by the Americans' parallel hole, showed rapid oscillations of temperature repeatedly at irregular intervals throughout the last glacial period. Greenland had sometimes warmed a shocking 7°C within a span of less than 50 years. For one group of American scientists on the ice in Greenland, the ‘moment of truth’ struck on a single day in midsummer 1992 as they analyzed a cylinder of ice, recently emerged from the drill hole, that came from the last years of the Younger Dryas. They saw an obvious change in the ice, visible within three snow layers, that is, scarcely three years! The team analyzing the ice was first excited, then sobered — their view of how climate could change had shifted irrevocably. The European team reported seeing a similar step within at most five years (later studies found a big temperature jump within a single year). ‘The general circulation [of the atmosphere] in the Northern Hemisphere must have shifted dramatically,’ Dansgaard’s group eventually concluded."

It was necessary to determine if these variations could be found in other locations in order to associate global change with the Greenland observations.
"The first results, from the Norwegian Sea in 1992, confirmed that the abrupt changes seen in Greenland ice cores were not confined to Greenland alone. Later work on seabed cores from the California coast to the Arabian Sea, and on chemical changes recorded in cave stalagmites from Switzerland to China, confirmed that the oscillations found in the Greenland ice had been felt throughout the Northern Hemisphere."

Once the data was in hand, scientists began to hypothesize about possible causes. They were able to identify a disturbingly large number of potential triggers. It was also recognized that existing climate models were not likely to be able to predict such rapid transitions. In the simplest words possible: small things can have big effects, and one thing can lead to another.

Hardly a day goes by that there isn’t some news release discussing the thinning arctic ice cap, surprisingly rapid melting of the ice fields of Greenland and Antarctica, changes in oceanic flows, massive icebergs breaking off and floating away—all potential signs of accelerated climate change. One might want to start paying close attention.

The purpose of this piece was to give the reader something else to worry about besides the sorry state of the world’s economy. Now—don’t you feel better?