Paleo-perspectives on the “velocity” and magnitude of future climate changes

Abstract:

Projected future climate changes are likely to be rapid, and large enough in magnitude to lead to situations where the climates of many locations may lack analogues to present-day climate. Moreover, climates now widely expressed on the landscape may become infrequent, while other “novel” climates may become widespread. The implications of the speed and magnitude of the projected future climate changes for species distributions is not clear; while climate changes seem too large for species to “track,” paleoecological records suggest that species have successfully negotiated multiple large, rapid, climate changes in the past.

We examine the speed and magnitude of past climate changes using TraCE-21k transient climate simulations (at annual and decadal time steps) and PMIP3/CMIP5 “time-slice” simulations for 6 and 21 ka. The transient simulations allow the rate of climate change (over different time intervals) to be measured, along with the similarity (or lack thereof) of past climates with the present to be mapped, while the time-slice simulations provide a gauge of uncertainty in the estimates related to variations among models (or projections).

Using Euclidean distances calculated from seasonal and annual (land only) temperature variables, the climates of recent decades compared with those over the last 22 kyr show an expexted increase in dissimilarity with the present climate as one goes farther back in time, with some important regional and temporal variations. Southern Hemisphere temperatures are more like those at present back to 11 ka than those in the Northern Hemisphere and tropical temperatures are less different from present during glacial times than those at mid- and high-latitudes. In both hemispheres, abrupt millennial time-scale variations are evident, with Antarctic Cold Reversal and Younger Dryas chronozones temperatures as different from present as those during the LGM. In the Northern Hemisphere, late-Holocene decadal-to-centennial variations frequently result in climates as different from present as those in the early Holocene or late glacial. Overall, the paleo record shows numerous examples of rapid, large-magnitude climate changes and we describe the significance of these changes for improving understanding of potential future climate change.