One of the wondrous paradoxes of the global cryosphere is that feather-like snowflakes can come together over time to build landscape features as dramatic and massive as the Antarctic ice sheet. Glaciers and ice sheets are a merger of meteorology and geology: a creation of the atmosphere that takes on a solid permanence on times-cales of centuries to millions of years. One of the unsettling aspects of recent climate change is the evidence that mountain glaciers and polar ice sheets may not be as permanent and ponderous as previously thought. Through atmospheric and oceanic forcing on glacier mass balance, surface meltwater effects on glacier dynamics, and positive feedbacks involved in both mass balance and ice-dynamical processes, glaciers and ice sheets can be surprisingly responsive to climate variability.

I have dedicated extra pages to the discussion of glacier and ice sheet dynamics, as this is a rich topic that still begs greater understanding with respect to Earth's climate system. The research community is in early stages in its representation of glaciers and ice sheets in climate models, but there is increasing awareness that this element of the global cryosphere has an important role to play in future changes in climate and sea level. I elaborate on this important topic in chapters 8 and 9, with an overview of the role that ice sheets have played in climate dynamics throughout Earth history.

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