We have a new paper out in Nature Climate Change on potential changes in natural unforced variability of global mean surface air temperature (GMST) under global warming.
Unforced GMST variability is of the same order of magnitude as current externally forced changes in GMST on decadal timescales. Thus, understanding the precise magnitude and physical mechanisms responsible for unforced GMST variability is relevant for both the attribution of past climate changes to human causes as well to the prediction of climate change on policy relevant timescales.
Much research on unforced GMST variability has used modeling experiments run under “preindustrial control” conditions or has used observed/reconstructed GMST variability associated with cooler past climates to draw conclusions for contemporary or future GMST variability. These studies can implicitly assume that the characteristics of GMST variability will remain the same as the climate warms. In our research, we demonstrate in a climate model that this assumption is likely to be flawed. Not only do we show that the magnitude of GMST variability dramatically declines with warming in our experiment, we also show that the physical mechanisms responsible for such variability become fundamentally altered. These results indicate that the ubiquitous “preindustrial control” climate modeling studies may be limited in their relevance for the study of current or future climate variability.
Another principal finding of our study is that global warming may cause local temperature variability to increase over low-to-mid latitude land regions at the same time that global temperature variability dramatically decreases. This represents a cause for concern, as it is precisely these low-to-mid latitude land regions that are characterized by the highest human population density and biodiversity.