Jan. 22, 2007 — Some of the perennially frozen ground high in the Himalayas has been shrinking, say Japanese scientists.
The year-round frozen "permafrost" ground was found to start at 17,000 to 17,400 feet above sea level (ASL) on the south-facing slopes of Nepal's Khumbu Himal in 1973, but is now at 17,700 to 18,000 feet (ASL), report Kotaro Fukui and his colleagues in the February issue of the journal Global and Planetary Change. Oddly enough, another measurement of the permafrost there in 1991 showed the same lower limit as 2004.
"Thus, it is possible that the permafrost lower limit has risen 300 to 1,000 feet (100 to 300 meters) between 1973 and 1991, followed by a stable limit of 17,700 to 18,000 feet (5400 to 5500 meters) over the last decade," the researchers report.
The likely cause of the thaw is global warming, which appears to be affecting the south-facing Khumbu Himal more quickly than on the nearby Tibetan Plateau, explains Fukui, a researcher at Japan's National Institute of Polar Research. Unfortunately, because the researchers have only three permafrost snapshots to judge by — 1973, 1991 and 2004 — there's just not enough data available to say much more about what's going on.
"That's the problem with any climate study: too little data," said climatologist Oliver Frauenfeld of the National Snow and Ice Data Center. Many places that are likely to see the greatest changes from global warming are in remote mountains or polar regions which are hard to monitor closely.
Besides just indicating climate changes, thawing permafrost poses special problems in mountainous regions. Thawed mountainsides that contain water are more likely to slide than permanently frozen ground, in which water is just another solid mineral, Frauenfeld explained.
On flat permafrost regions of the Arctic or Tibet, for example, thawing can cause roads and railroad tracks to buckle and building foundations to sink or collapse.
The good news, says Frauenfeld, is that even with the worse-case climate warming scenario, most permafrost in the world today would still be permafrost. In places like the Russian Arctic, for instance, a rise of -40 degrees to -30 degrees is a lot — but it's still frozen.
Compared to the total area of frozen ground on Earth, said Frauenfeld, "The changes we're seeing in the permafrost regions are not that big."
The places most affected are those that are now hovering just under freezing in summer, which are at the fringes of the world's permafrost zones, Frauenfeld said.
