Attributing decadal variability in surface temperatures and precipitation to the Northern Hemisphere stratospheric polar vortex

 
The role of the stratosphere for decadal variability of surface climate is isolated using  two sets of simulations in four different coupled ocean-atmosphere climate models. In the first set,  the stratosphere (above 100hPa only) is nudged to observations (NUDGED) while allowing for the rest of the atmosphere to evolve freely, while in the second set the ocean-atmosphere system is free-running (FREE) and  the stratospheric polar vortex does not exhibit any long term trends. By comparing NUDGED to FREE, we  attribute   to the stratosphere the anomalously cold conditions in the 2000s in high latitude Eurasia, and also the contemporaneous warm conditions in Eastern Canada. Furthermore, anomalously rainy conditions in much of Southern Europe in the 2000s can also be attributed to the stratosphere. This fingerprint from the stratosphere overwhelmed any forced signal from anthropogenic emissions.