12 December 2007
Missing Fallout Fuels Warming Fears
by Kate Melville
Ice cores drilled from the Himalayas lack the distinctive radioactive traces that atomic explosions produce, possibly indicating that no new ice has accumulated since the 1950s, attendees at the annual meeting of the American Geophysical Union were told recently. The missing radioactivity, originating as fallout from atmospheric nuclear tests during the 1950s and 1960s, routinely provides researchers with a benchmark against which they can gauge how much new ice has accumulated on a glacier or ice field.
Scientists believe that the missing signal means that this Tibetan ice field has been shrinking at least since A-bomb testing began half a century ago. If true, it could foreshadow a future when the stockpiles of freshwater will dwindle and vanish, seriously affecting the lives of more than 500 million people on the Indian subcontinent.
Thompson and his colleagues worry that this massive loss of meltwater would drastically impact major Indian rivers like the Ganges, Indus and Brahmaputra that provide water for one-sixth of the world's population.
"There's about 12,000 cubic kilometers (2,879 cubic miles) of fresh water stored in the glaciers throughout the Himalayas - more freshwater than in Lake Superior," explained Lonnie Thompson, distinguished university professor of earth sciences at Ohio State University. "Those glaciers release meltwater each year and feed the rivers that support nearly a half-billion people in that region. The loss of these ice fields might eventually create critical water shortages for people who depend on glacier-fed streams."
Thompson explained that usually, radioactivity signals are present in ice cores retrieved from both polar regions and from tropical glaciers around the globe, indicating that those ice fields have retained snow (mass) over the last 50 years. "In ice cores drilled in 2000 from Kilimanjaro's northern ice field (5890 meters high), the radioactive fallout from the 1950s atomic test was found only 1.8 meters below the surface," he noted. "By 2006 the surface of that ice field had lost more than 2.5 meters of solid ice (and hence recorded time) - including ice containing that signal. Had we drilled those cores in 2006 rather than 2000, the radioactive horizon would be absent - like it is now in the Himalayas," he said.
Scientists estimate that there are some 15,000 glaciers nested within the Himalayan mountain chain forming the main repository for fresh water in that part of the world. The total area of glaciers in the Tibetan Plateau is expected to shrink by 80 percent by the year 2030.
Source: Ohio State University