Eurasian wintertime cooling: New perspectives from an updated synthesis

Over a decade ago, researchers noticed that as the Arctic warmed rapidly, there was an apparent cooling over large areas of central Eurasia in the wintertime. Many theories were put forward suggesting that changes in wintertime sea-ice were linked to this observed cooling through some hereto unknown teleconnection. Numerous studies based on observations, reanalyses, and a vast array of modelling experiments have been undertaken to resolve this question. The ongoing debate regarding Arctic to mid-latitude teleconnections over the Eurasian sector has divided the scientific community, as highlighted by the work of Cohen et al. [2020], primarily between those in favour of sea-ice having a key role in giving rise to the cooling, and those who believe the cooling is primarily the result of internal atmospheric variability. While Eurasian cooling itself has mostly ended, the debate continues due to a desire to better understand the teleconnections underlying Northern Hemisphere climate variability.

Here we discuss a new synthesis study into Eurasian cooling, undertaken by an extensive team at the Bjerknes Centre over the past two years. The work breaks down the debate into a simple structure, examining first the findings of the observational-based studies and the modelling-based studies separately. In evaluating this body of literature, we attempt to avoid categorizing studies based on the researchers’ interpretations of their findings, and focus where possible on only the facts of what their analyses and simulations show. This has allowed us to reconcile some of the apparently conflicting results in the literature. To be clear, we do not present a new mechanistic understanding of the processes underlying Eurasian cooling. However, laying out the existing research in an objective and structured manner has allowed us to propose a new framework within which to view the problem, wherein we clarify the distinct roles of internal variability and an external (sea-ice driven) forcing of Eurasian cooling.