The combined impacts of natural climate variability and global warming will define how we experience 21st century climate change. If natural, interdecadal climate variability is strong relative to global warming, our future climate path may unfold like a jagged staircase. By contrast, if internal climate variability is weak relative to forced climate change, our future climate path may be more smooth. Despite the importance of interdecadal climate variability for determining this future climate path, we have a limited understanding of which regions are driving decade-long warming and cooling shifts in global surface air temperature. It is difficult to study temperature variations lasting decades to centuries because instrumental observations tend to be too short, and climate model simulations often disagree on regional sources of natural climate variability. Here I use a new data set, the Last Millennium Reanalysis (LMR), that combines pre-instrumental (paleoclimate) records with climate model data to extend our knowledge of past climate variations and what may be causing them. The LMR climate field reconstructions suggest that regions of the North Pacific and North Atlantic oceans are associated with global temperature variations on decadal timescales.