E11 Atmosphere - Cryosphere Interaction

Topic

The cryosphere—comprising sea ice, glaciers, snow, and permafrost—interacts with the atmosphere through both radiative and dynamic feedbacks that are crucial to the current and future climate system. The most direct of these is the ice-albedo feedback: ice can reflect between half and more than eight-tenths of the solar radiation it receives—far more than the open ocean, which reflects barely six to ten percent of that same radiation, or vegetation, which reflects between ten and twenty-five percent. When sea ice is lost, the newly exposed surface—open ocean instead of ice—absorbs significantly more solar radiation than before; this increased absorption warms the surface further, and that additional warming melts even more sea ice, completing a positive feedback loop that amplifies climate change in polar regions.

This ice-albedo feedback is one of the mechanisms driving Arctic polar amplification, the phenomenon whereby the Arctic warms two to four times faster than the global average. In addition to the ice-albedo feedback, three other mechanisms contribute to Arctic polar amplification: the loss of latent heat from sea freezing—which under normal conditions remains trapped beneath a near-surface temperature inversion layer but is reduced when less new ice forms; the increase in atmospheric water vapor, which, like any other greenhouse gas, traps more longwave radiation near the surface; and the redistribution of oceanic heat, which transports heat from lower latitudes to the Arctic. All this additional warming experienced by the Arctic reduces the meridional temperature gradient between the Arctic and mid-latitudes; this reduction in the gradient, in turn, has dynamic consequences for the rest of the atmosphere: it weakens the wind jets sustained by that very gradient and can increase the amplitude of Rossby waves traveling along those weakened jets. Furthermore, higher-amplitude Rossby waves move more slowly, and this sluggishness causes the associated weather extremes to persist longer over a given region.

Continental snow cover produces effects very similar to those of sea ice, albeit over land rather than the ocean. It modifies the surface albedo just as sea ice does, triggering its own snow-albedo feedback; it increases the stability of the overlying atmospheric boundary layer, inhibiting convection much like any cold, stable surface; and it affects the region's hydrological cycle by storing water in solid form during winter and releasing it later when the snow melts in spring, rather than allowing immediate runoff as rain would.

Thus, the cryosphere—whether as sea ice that is lost and thereby amplifies its own loss, as continental snow that modulates albedo and retains water, or as permafrost and glaciers forming part of the same system—ultimately shapes both the radiative balance and the dynamics of the overlying atmosphere. It is precisely this dual influence—radiative and dynamic—that makes the interaction between the cryosphere and the atmosphere one of the most sensitive components of the climate system.

ID:1402