The beautiful and the dammedGetty Images  THE Arctic tundra is
one of the world's most extensive ecosystems, and the frozen
soil known as permafrost, which underlies it, can be hundreds of
metres deep. But as the world warms up in response to the
millions of tonnes of carbon dioxide and other greenhouse gases
being poured into the atmosphere each year, so does the
permafrost. As the permafrost thaws, bacteria start chewing up
the organic matter it contains. This releases yet more carbon
dioxide, as well as methane, another greenhouse gas, which has
25 times the warming potential of CO2. Edward Schuur of the
University of Florida in Gainesville, a doyen of the field,
estimates that the world's permafrost contains twice as much
carbon as its atmosphere. If even a fraction of that were
released as CO2 and methane, it would be bad news.  Nor is that
all. Thawing permafrost also leaks nitrates and phosphates into
the tundra, allowing novel plant species to get a foothold in
what was, to start with, a fairly sparta