Editing IPCC:AR6/SROCC/Chapter-3 (section)

===== 3.4.1.3.1 Freshwater ice =====

Long-term ''in situ'' river ice records indicate that the duration of ice cover in Russian Arctic rivers decreased by 7–20 days between 1955 and 2012 (Shiklomanov and Lammers, 2014 <sup>[[#fn:r1459|1459]]</sup> ) ( ''high confidence'' ). This is consistent with historical reductions in Arctic river ice cover derived from models (Park et al., 2015) and regional analysis of satellite data (Cooley and Pavelsky, 2016 <sup>[[#fn:r1461|1461]]</sup> ).

Analysis of satellite imagery between 2000 and 2013 identified a significant trend of earlier spring ice break-up across all regions of the Arctic (Šmejkalová et al., 2016 <sup>[[#fn:r1462|1462]]</sup> ); independent satellite data showed approximately 80% of Arctic lakes experienced declines in ice cover duration during 2002–2015, due to both a later freeze-up and earlier break-up (Du et al., 2017 <sup>[[#fn:r1463|1463]]</sup> ) ( ''high confidence'' ). There are indications that lake ice across Alaska has thinned in recent decades (Alexeev et al., 2016 <sup>[[#fn:r1464|1464]]</sup> ), but ice thickness trends are not available at the pan-Arctic scale. Analysis of satellite data over northern Alaska show that approximately one-third of bedfast lakes (the entire water volume freezes by the end of winter) experienced a regime change to floating ice over the 1992–2011 period (Surdu et al., 2014 <sup>[[#fn:r1465|1465]]</sup> ; Arp et al., 2015 <sup>[[#fn:r1466|1466]]</sup> ). This can result in degradation of underlying permafrost (Arp et al., 2016 <sup>[[#fn:r1467|1467]]</sup> ; Bartsch et al., 2017 <sup>[[#fn:r1468|1468]]</sup> ). Lakes of the central and eastern Canadian High Arctic are transitioning from a perennial to seasonal ice regime (Surdu et al., 2016 <sup>[[#fn:r1469|1469]]</sup> ).

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