Galaxy - Progressive

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.

Dansgaard et al. (1989); increasingly abrupt changes were seen on further study, Johnsen et al. (1992); Grootes et al. (1993); jumps of Greenland snow accumulation "possibly in one to three years" were reported by Alley et al. (1993), see also Mayewski (1993); five-year steps: Taylor et al. (1997); changes in dust had been noted, indicating at least continental scope for the change, and a Younger Dryas temperature step in less than a decade was found to be hemisphere-wide since methane gas changed as well: Severinghaus et al. (1998). Good histories are Alley (2000) and Cox, (2005), ch. 8.

http://www.aip.org/history/climate/rapid.htm