Global temperatures have been increasing over the past few decades, though the warming is asymmetric with some geographic regions warming over time even as others slightly cool. For example, scientists have observed a “wavy pattern” of temperature trends over the mid-latitudes of the Northern Hemisphere known as the warm Arctic cold Eurasia pattern (WACE). Reasons for this asymmetry have been a major topic of study. A recent study, published in the Journal of Climate, suggests that asymmetric temperature trends like WACE are driven partially by internal climate variability originating from the tropics. The study’s authors refer to this tropically-driven global teleconnection, or climate outcomes linked over long distances, as the Interdecadal Pacific Oscillation-related Bipolar Teleconnection (IPO-BT).
This study, funded by CPO project awards from both the Climate Variability and Predictability (CVP) program and the Modeling, Analysis, Predictions and Projections (MAPP) program, provides new evidence that a cooling signal over Eurasia may be associated with low-frequency tropical sea surface temperature variability. Due to a lack of records, scientists have not had the necessary data to study tropical sea surface temperatures on longer-term timescales. However, two recently-developed paleo-reanalysis datasets reconstruct past atmospheric circulation patterns from up to 2,000 years ago. Using these paleo datasets, along with multiple contemporary climate models, allows researchers to see if the IPO-BT pattern observed in recent decades is a recurring pattern over hundreds of years. The study results show that the IPO-BT has a consistent and prominent role in shaping global temperature variability over the past 400-2,000 years.