Earth & Environment

Climate change brings a thirstier West and thinner polar bears, plus parsing the sun and moon's effects in this week's news

Polar bears’ ice-melt diet

For polar bears, the loss of summer sea ice can be a slimming experience. The melting of ice floes eliminates resting spots and forces the bears to swim substantially more. One radio-tagged female lost a cub and almost one-quarter of her body weight over a roughly two-month period in late summer to early fall of 2008. Federal and university scientists from Alaska and Wyoming tracked her traveling almost 2,500 kilometers during that time, including one nine-day stint when she swam continuously — covering 687 kilometers. Such marathon travels would appear to compromise the health and fitness of this beleaguered species, the scientists argue in the July Polar Biology.Janet Raloff

Celestial climate

The moon and the sun influence Earth’s climate at different times of year, a new study suggests. Researchers have analyzed month-to-month changes in the temperature gradient between the poles. The changes varied every 11 years in winter — meaning the sun was the driving force with its 11-year solar cycle — and 18.6 years in summer — meaning the moon dominated then. Basil Davis, of the École Polytechnique Féderal de Lausanne in Switzerland and Simon Brewer of the University of Wyoming in Laramie describe the work in an upcoming Quaternary Science Reviews. Alexandra Witze

West may get much thirstier

The primary water source for the Colorado, Columbia and Missouri Rivers — and more than 70 million Americans — has been diminishing at a nearly unprecedented rate and breadth over the last half century, U.S. and Canadian researchers report. They analyzed tree-ring data going back 800 years in the Northern Rockies to reconstruct regional climate. Although precipitation rates seesawed through the centuries, snowpack shrinkage during the latter 20th century was the most dramatic, the scientists report in the June 9 Science. With temperature now appearing to outrank precipitation rates as the leading influence on water storage, the researchers say, current warming trends threaten Western water security. —Janet Raloff

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