Exploring the impact of climate change for biological climate variables using observations and multi-model initial condition large ensembles

Species are expected to shift their distributions to higher latitudes, greater elevations, and deeper depths in response to climate change, reflecting an underlying hypothesis that species will move to cooler locations.  However, there is significant variability in observed species range shifts and differences in exposure to climate change may explain some of the variability amongst species.  But this requires identifying regions that have experienced detectable changes in those aspects of the climate system that species are sensitive to. 

To better understand species exposure to climate change, we estimate the time of emergence of climate change for 19 biologically relevant climate variables using observations and initial condition large ensembles from five different climate models.   The time of emergence (ToE) is calculated using Signal/Noise (S/N) thresholds.  The S/N threshold applied in this study is >=2, but this threshold can be easily modified to represent species that are more or less sensitive to climate change.  Preliminary findings from the initial condition large ensembles indicates the strongest emergence for the temperature metrics within the tropical oceanic regions in the absence of upwelling. The earliest emergence over the oceans is found within the western warm pool of the Pacific.  Notable places that haven’t emerged for the temperature metrics include both the North Atlantic and Pacific.  The ToE of a climate change signal for the temperature metrics over land is spatially complex, which may partially explain the complex observed range shifts for terrestrial species.  For instance, multiple initial condition large ensembles indicate a signal has emerge in the most recent decades only for the western and northeastern parts United States.