Since the 1950s many of the observed changes are unprecedented over decades to millennia. (sciencedaily.com)
Snow - cover and sea - ice can change quite rapidly, but glaciers and ice - sheets may require decades to millennia. (usask.ca)
It is very likely much of the current glacial meltwater will then take decades to millennia to reach the ocean and has yet to impact modern sea levels. (landscapesandcycles.net)