Arctic Ice Cover, Ice Thickness and Tipping Points

Abstract

We summarize the latest results on the rapid changes that are occurring to Arctic sea ice thickness and extent, the reasons for them, and the methods being used to monitor the changing ice thickness. Arctic sea ice extent had been shrinking at a relatively modest rate of 3-4% per decade (annually averaged) but after 1996 this speeded up to 10% per decade and in summer 2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million km(2). Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially rapid loss of mass from pressure ridges. The summer 2007 event may have arisen from an interaction between the long-term retreat and more rapid thinning rates. We review thickness monitoring techniques that show the greatest promise on different spatial and temporal scales, and for different purposes. We show results from some recent work from submarines, and speculate that the trends towards retreat and thinning will inevitably lead to an eventual loss of all ice in summer, which can be described as a 'tipping point' in that the former situation, of an Arctic covered with mainly multi-year ice, cannot be retrieved.

Experimentally determined temperature thresholds for Arctic plankton community metabolism

“…Such a steep rate of warming has resulted in severe reduction of ice cover, exceeding the range of natural variability over the past millennia and creating potentially dangerous positive feedbacks (Walsh, 2008;Duarte et al, 2012). Rapid warming is expected to continue in the future, with up to 6 • C warming throughout the 21st century (ACIA, 2004), and revised forecasts suggest that the Arctic will be ice free in the summer before 2050 (Holland et al, 2006;Boé et al, 2009;Wang and Overland, 2009;Wadhams, 2012). The ice cover over the Arctic Ocean reached a historical minimum in September 2007 with a reduction of 43 % relative to the ice cover in 1979 (Kerr, 2007).…”

“…In 2012 ice cover again approached this historical minimum (National Snow and Ice Data Center, 2011 available at: http://nsidc.org/). Sea ice is not only changing in extent, but is also decreasing in thickness (Johannessen et al, 1999;Kwok and Rothrock, 2009;Wadhams, 2012) as well as increasing in the duration of the ice melt season (Belchansky et al, 2004). These factors are expected to affect the primary productivity in the region by changing light regimes or affecting the timing of the spring bloom (Wassmann et al, 2006(Wassmann et al, , 2008Ellingsen et al, 2008).…”

Snow depth on Arctic sea ice from historical in situ data

“…One of the characteristic trends is the reduced amount of ice that survives summer melt (Comiso, 2012;Stroeve et al, 2012;Parkinson and Comiso, 2013;Kwok and Cunningham, 2015;Wang et al, 2016). This is closely connected with the thinning of the sea ice (Kwok and Rothrock, 2009;Kwok and Cunningham, 2015;Wadhams, 2012) and the change in the ice age distribution with less MY ice and more FY ice (Tschudi et al, 2016). Later onset of freeze (Stroeve et al, 2014) and correspondingly later start of snow accumulation is the last but 15 not the least factor that determine snow depth distribution in present time (Wang et al, 2013;Webster et al, 2014).…”

“…But ridges and hummocks are also 30 changing over last decades due to less MY ice and more FY ice. According to Wadhams (2012), the reduction in ice The Sever expeditions represented a unique observing programme in the Arctic, which is not likely to be repeated anytime in the future. Present and future observations of snow and sea ice will rely on satellites, aircraft and automated buoys, as described in Sect.…”

Climate Policy Implications of Nonlinear Decline of Arctic Land Permafrost and Sea Ice

“…The US's withdrawal from the current national pledges could increase the total discounted economic impact of the two Arctic feedbacks until 2300 by $25 trillion, reaching nearly $120 trillion, while meeting the 1.5 °C and 2 °C targets will reduce the impact by an order of magnitude. from thawing permafrost, i and the sea ice-albedo feedback (SIAF) 8,9 increases solar absorption in the Arctic Ocean. Despite significant advances documented by the 5 th IPCC Assessment Report, projections of future climate using state-of-the-art Earth system models (ESMs) from the CMIP5 project do not include PCF, 10,11 although several models will incorporate the PCF in the 6 th assessment report.…”