Photo: Esko Kuusisto
River and Lake Ice
Changes that have largely mirrored rising air tempera- port corridors and longer ice-free periods mean reduced
tures are affecting river and lake ice, mainly seen as or more expensive access to communities and industrial
earlier spring break up and, to a lesser extent, later au- developments. Many northern indigenous people de-
tumn freeze up. pend on frozen lakes and rivers for access to traditional
The trend to longer ice-free periods is projected to con- hunting, fishing, reindeer herding or trapping areas.
tinue. Details are uncertain but strong regional varia- Spring break up often causes damming of rivers by
tion is expected, with the amount of change depending ice, resulting in costly flooding. Lowered temperature
on the degree of warming that is forecast. gradients along north-flowing rivers in the Northern
Ice formation on rivers and lakes is a key factor control- Hemisphere may lead to reductions in ice-jam flood-
ling biological production and changes in the length ing. This has potential negative ecological consequenc-
and timing of ice cover have ecosystem effects. es for deltas where annual flooding is needed to main-
In remote areas frozen rivers and lakes are used as trans- tain ponds and wetlands.
16 GLOBAL OUTLOOK FOR ICE AND SNOW