Abstract
Abstract. Changes in the atmospheric moisture transport have been proposed as a vehicle for interpreting some of the most significant changes in the Arctic region. The increasing moisture over the Arctic during the last decades is not strongly associated with the evaporation that takes place within the Arctic area itself, despite the fact that the sea ice cover is decreasing. Such an increment is consistent and is more dependent on the transport of moisture from the extratropical regions to the Arctic that has increased in recent decades and is expected to increase within a warming climate. This increase could be due either to changes in circulation patterns which have altered the moisture sources, or to changes in the intensity of the moisture sources because of enhanced evaporation, or a combination of these two mechanisms. In this short communication we focus on the more objective assessment of the strong link between ocean evaporation trends and Arctic Sea ice melting. We will critically analyse several recent results suggesting links between moisture transport and the extent of sea ice in the Arctic, this being one of the most distinct indicators of continuous climate change both in the Arctic and on a global scale. To do this we will use a sophisticated Lagrangian approach to develop a more robust framework on some of these previous disconnecting results, using new information and insights. Results reached in this study stress the connection between two climate change indicators, namely an increase in evaporation over source regions (mainly the Mediterranean Sea, the North Atlantic Ocean and the North Pacific Ocean in the paths of the global western boundary currents and their extensions) and Arctic ice melting precursors.
Highlights
The last IPCC Assessment Report has confirmed that the main components of the climate system have been warming or shrinking since the 1970s, as a result of global warming induced by the significant increment in concentration of greenhouse gases of anthropogenic origin (AR5, IPCC, 2013)
Both indicators (AST and sea ice extent (SIE)) may respond to other mechanisms including changes in atmospheric circulation patterns (Graversen et al, 2008), ocean circulation (Comiso et al, 2008), and changes in radiative fluxes associated with cloud cover and water vapour content in the atmosphere (Schweiger et al, 2008; Kapsch et al, 2013), through the absorption of the outgoing long-wave radiation from the surface by the increased atmospheric moisture and remitted toward the Arctic surface, resulting in the surface warming and sea ice decline (Kapsch et al, 2013)
For instance the autumn and early positive trend is snow cover extent (SCE) (Estilow et al, 2015), which can be closely related to positive trends in Eurasian rivers (Yang et al, 2007). Two of these works (Zhang et al, 2012; Kapsch et al, 2013) provide novel insight on the role played by the transport of moisture and the melting of sea ice or snow cover. Their main findings are summarized below: 1. According to Zhang et al (2012) in their work entitled “Enhanced poleward moisture transport and amplified northern high-latitude wetting trend”, the authors provide strong evidence to support (i) that there is a trend in the net poleward atmospheric moisture transport (AMT) towards the Eurasian Arctic river basins, (ii) that this net AMT is captured in 98 % of the gauged climatological river discharges, and (iii) that the upward trend of 2.6 % net AMT per decade is in good agreement with the 1.8 % increase per decade in the gauged discharges
Summary
The last IPCC Assessment Report has confirmed that the main components of the climate system have been warming (atmosphere, oceans) or shrinking (cryosphere) since the 1970s, as a result of global warming induced by the significant increment in concentration of greenhouse gases of anthropogenic origin (AR5, IPCC, 2013). The recent rise on the incidence of summer extreme weather events over Northern Hemisphere continental land masses (Coumou and Rahmstorf, 2012; Seneviratne et al, 2014) is probably driven by the accelerated decline of summer SIE and SCE observed in recent decades (Francis and Vavrus, 2012; Tang et al, 2014) According to this hypothesis, the observed weakening of poleward temperature gradient triggered changes in atmospheric circulation, namely slower progression of Rossby waves (Francis and Vavrus, 2012) and the existence of a planetary-scale wave life cycle (Bagget and Lee, 2015) that is highly amplified (blocking) despite a reduced meridional temperature gradient (consistent with Francis and Vavrus, 2012). Considering all the above reasons the Arctic sector emerges as the most sensitive region of the climate system to the effects of global warming, but it represents an area where current and future changes are bound to affect the climate at a much larger scale (Screen and Simmonds, 2010; Tang et al, 2014; Cohen et al, 2014)
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