Recent Arctic amplification and extreme mid-latitude weather

Abstract

NATURE GEOSCIENCE | ADVANCE ONLINE PUBLICATION | www.nature.com/naturegeoscience 1 T he Arctic cryosphere is an integral part of Earth's climate system and has undergone unprecedented changes within the past few decades. Rapid warming and sea-ice loss has had significant impacts locally, particularly in late summer and early autumn. September sea ice has declined at a rate of 12.4% per decade since 1979 (ref. 1), so that by summer 2012, nearly half of the areal coverage had disappeared. This decrease in ice extent has been accompanied by an approximately 1.8 m (40%) decrease in mean winter ice thickness since 1980 (ref.2) and a 75-80% loss in volume 3 . Though sea-ice loss has received most of the research and media attention, snow cover in spring and summer has decreased at an even greater rate than sea ice. June snow cover alone has decreased at nearly double the rate of September sea ice 4 . The decrease in spring snow cover has contributed to both the rise in warm season surface temperatures over the Northern Hemisphere extratropical landmasses and the decrease in summer Arctic sea ice 5 . The combined rapid loss of sea ice and snow cover in the spring and summer has played a role in amplifying Arctic warming. However, snow cover and sea-ice trends diverge in the autumn and winter with sea ice decreasing in all months while snow cover has exhibited a neutral to positive trend in autumn and winter 6 . Climate change and Arctic amplificationWhile the global-mean surface temperature has unequivocally risen over the instrumental record 7 , spatial heterogeneity of this warming plays an important role in the resulting climate impacts. In particular, the near-surface of the Northern Hemisphere high latitudes are warming at rates double that of lower latitudes [8][9][10] . This observed The Arctic region has warmed more than twice as fast as the global average -a phenomenon known as Arctic amplification. The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover, at a pace greater than that simulated by climate models. These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes, including severe winters. The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation. Through changes in these key atmospheric features, it is possible, in principle, for sea ice and snow cover to jointly influence mid-latitude weather. However, because of incomplete knowledge of how high-latitude climate change influences these phenomena, combined with sparse and short data records, and imperfect models, large uncertainties regarding the magnitude of such an influence remain. We conclude that improved process understanding, sustained and additional...

Winter 2015/16: A Turning Point in ENSO-Based Seasonal Forecasts

“…Not only was snow cover unusually extensive, but the September 2015 Arctic sea ice extent was the fourth lowest observed, and the November 2015 Barents-Kara sea ice extent was the third lowest since 1979. The high autumn snow cover and low Arctic sea ice were eventually followed by an abnormally weak polar vortex, a sudden stratospheric warming (SSW) event, a negative AO, and cold temperatures across parts of the Northern Hemisphere mid-latitudes during mid-winter, all of which are consistent with the mechanism outlined by Cohen et al (2014b). A weak polar vortex and negative AO were also found to be favored during El Niño winters (Ineson and Scaife, 2009).…”

“…Other model-based studies found an insensitivity to Arctic forcings such as sea ice and snow cover (Hardiman et al, 2008;McCusker et al, 2016), so it remains an open question whether the models are deficient in simulating the atmospheric response to Arctic forcings. Another important atmospheric response attributed to amplified Arctic warming is a weakened polar vortex during middle to late winter (Cohen et al, 2014b;Kim et al, 2014). The weakened polar vortex is caused by increased poleward heat and equatorward momentum transport related to increased upward vertical wave activity flux (WAFz) and is associated with a stronger Siberian high (Cohen et al, 2007;Jaiser et al, 2012).…”

“…Progress in understanding this connection has converged on two key factors: (1) the variability of autumn snow cover in Eurasia, and (2) the variability of sea ice coverage in the BarentsKara Sea during late fall and early winter. Numerous recent studies based on both observations and model simulations indicate that reduced Barents-Kara sea ice in late fall favors a strengthened and northwestward expansion of the Siberian high, increased poleward heat flux, weakened polar vortex, and ultimately a negative AO (Cohen et al, 2014b, and references therein). Because low Barents-Kara sea ice and high Eurasian snow cover favor northwestward expansion of the Siberian high, this atmospheric pattern increases the probability of driving cold Siberian air southeastward into populous East Asia.…”

Mechanisms influencing seasonal to inter-annual prediction skill of sea ice extent in the Arctic Ocean in MIROC

“…The Arctic has warmed more than twice as much as the global average (e.g., Bekryaev et al, 2010;Cohen et al, 2014), this is referred to as Arctic amplification. Sea ice reduction resulting from climate change is one of the main processes contributing to Arctic amplification (e.g., Pithan and Mauritsen, 2014).…”

Evaluation of CORDEX-Arctic daily precipitation and temperature-based climate indices over Canadian Arctic land areas

“…While total precipitation is generally low over much of the Canadian Arctic (the Arctic islands being known as Arctic desert) (Serreze and Barry 2005;Stern and Gaden 2015), increases in extreme precipitation events and precipitation intensity have been observed over the Arctic (Cohen et al 2014;Ye et al 2015;Wan et al 2015) and further increases are expected in response to warming and increasing atmospheric humidity from reductions in sea ice extent. Therefore part of this paper is devoted to evaluating model skill in simulating the upper-tail of daily-precipitation annual distributions (Rx1day, Rx5day, R95ptot and R99ptot) and one related to the number of wet days (R1mm), with a wet day defined as a day with Maximum 1-day precipitation amount (annual maximum of daily precipitation) mm/day 2 mm/day RX5day…”