Of all the "spheres" that we deal with in BAMS, the "cryosphere" may be the most nebulous. Certainly, it is the least spherical, geometrically and geographically: it encompasses a very disparate set of environments and places. The cryosphere is also home to some of geophysics' most intriguing and important paradoxes; for instance, the fact that water gets denser as it gets colder-until it gets cold enough to float and freeze. Or that a warming world might actually increase snow and glaciers, in places, because of increasing precipitation. People celebrate biodiversity, but there is also a kind of "cryodiversity" that makes this planet what it is.
The word cryosphere itself is rarely shared with the public, however; it sounds cool but doesn't mean cool to most people-that may explain why the online game at Cryosphere.net is about space stations and not snow and ice. Yet all over the world the real cryosphere has been news of late, as much for its amorphousness as for any other of its elusive properties. Initially this year a Long Island-sized iceberg drifted toward a major collision with part of the Antarctic sheet and for a while captured media attention as a cataclysmic sign of global warming, or at least as an epic demolition derby.
Less startling have been the snowbound travelers or the newsworthy cryospheric activity threatening citrus in Florida and tractionless drivers in Las Vegas, Nevada, of all places. And during the spate of wet weather in the West, many eyes were diverted from deadly mudslides to the status of long-term drought, epitomized by the replenishment of the Sierra snowpack.
On its Web site, the National Snow and Ice Data Center makes clear that the cryosphere in this part of the globe is declining (now, per decade, about 3% less annual snow and polar sea ice extent in the Northern Hemisphere). The recent Arctic Climate Impact Assessment discusses many changes in the cryosphere, including the melting of permafrost. The changes in the Arctic tend to dwarf subtle climatic trends elsewhere, which means the cryosphere seems to bear the brunt of warming of the global system.
However, there's much confusion in the public's mind about this eroding cryosphere-the difference between ice extent and thickness, for instance, or the relationship between regional and global trends. Perhaps local vegetation and land-use changes are reducing snow cover? In this issue, Philip Mote and colleagues look at the decline of mountain snows across the American West and conclude that climate warming is indeed "the dominant factor."
Studies like this will eventually help people get past the geographic discontinuities, the multiple forms, and the complex sensitivities of the cryosphere. It is elusive by nature; we seem to be making it more elusive than ever.
[Author Affiliation]
Jeff Rosenfeld, EDITOR-IN-CHIEF
Комментариев нет:
Отправить комментарий