The impact of Arctic amplification on the extratropical jets

Abstract

Since the 1990's, greenhouse gas forcing has warmed the Arctic at twice the rate of lower latitudes, coinciding with a dramatic decline in Arctic sea ice extent. This manifestation of climate change has ignited a lively and ongoing debate regarding if Arctic warming will significantly influence extreme weather in the extra-tropics. This thesis offers three distinct contributions to the dialogue. Firstly, results are presented from a suite of targeted climate model experiments designed to establish how ice-forced and snow-forced anomalies interact and propagate through the atmosphere. Results suggest that high snow anomalies can suppress the October-November atmospheric response by interfering with the forcing of hemispheric (wave one) atmospheric dynamics. Intriguingly, the simulations do not force the persistent stratospheric response reported in similar experiments. This may be a consequence of transient or seasonally-restricted surface forcing. Secondly, multi-model projections of future wintertime North Atlantic and North Pacific tropospheric jets are analyzed using a novel Bayesian weighting technique. This approach is shown to reduce systematic bias and indicates that future forcing of the jets - due to greenhouse gas emissions - will be first order linear (i.e. independent of historical bias). Results suggest that the widely reported future poleward shift at the level of the eddy-driven jet is far from robust. Lastly, an attempt is made to distill the current level of consensus within the scientific community using expert elicitation. Results reveal a fairly evenly split on if Arctic warming has already had a significant impact on the mid-latitude jets, but a strong consensus that it will in the future.