Abrupt methane releases from frozen regions may have played a major role in two events, 55 and 251 million years ago, that extinguished much of the life then on Earth.

BBC: Climate 'tech fixes' urged for Arctic methane

Bilateral military events that were in the planning phases have also been frozen.

WHITEHOUSE: Press Briefing

During hundreds of camping trips and meetings and service projects and weird and wonderful events such as the Klondike Derby (a cold-weather competition in which scouts drag makeshift sleds over frozen ground for hours), I learned how to adapt to changing circumstances on the fly while keeping the main goals in sight.

WSJ: A Lesson From the Scouts' Own Book