On the horizon

Greenland's ice melting faster

Greenland is losing its ice at an accelerating rate, according to new results from a research team at the University of Texas. The team acknowledges that the melt tempo may reflect natural variations. But, researchers add, if confirmed, their results also "would be consistent with proposed increases in global warming in recent years." If the island were to lose all its ice, average sea levels would rise by about 6.5 meters (21 feet), researchers estimate.

Scientists used the US-German GRACE satellites to measure changes in the gravity field over Greenland. The satellites provide the most accurate monthly estimate available for the gravity changes, which reflect changes in the amount of mass the ice cap presents. Initial measurements using other satellite techniques indicated Greenland was losing ice at a rate of 80 cubic kilometers a year from 1997 to 2003. Earlier this year, scientists reported that for 2005, the loss rate hit 224 cubic kilometers. The latest results show that from 2002 to 2005, the loss rate averaged 239 cubic kilometers a year.

"This melting process may be approaching a point where it won't be centuries before Greenland's ice melts, but a much shorter time," says Byron Tapley, an aerospace-engineering professor and the team's leader. The results appear in the current online issue of Science.

Polarized light is birds' 'compass'

Scientists have long been fascinated by birds' abilities to migrate long distances with enviable precision. But the directional cues birds take from Earth's magnetic field, polarized light high in the sky, stars, or the sun can send birds off in the wrong direction, too. They also can get thrown off by bad weather, changes in latitude, longitude, or other conditions.

Now a research team from Virginia Tech in Blacksburg, Va., appears to have discovered the method birds use to "calibrate" these various approaches to yield a coherent navigation system.

The team's experiments found that songbirds – in this case, Savannah sparrows – adjust their internal compasses against a particularly strong swath of polarized light that appears at sunrise and sunset. The band of light runs from horizon to horizon and from north to south at dawn and dusk. By checking this light near the horizon each morning and evening (weather permitting), then averaging the readings, the birds appear to get an independent measure of true north and south, regardless of latitude or time of year.

The team found that in the absence of these cues, birds relied more heavily on Earth's magnetic field to calibrate other navigation aids. The work appears in the current issue of the journal Science.

Flood-resistant rice

Scientists have found a rice gene that enables the plants to survive underwater for long periods of time, holding out the hope of rice that can withstand floods. Floods destroy an estimated $1 billion in rice crops worldwide every year.

Rice – a key source of nutrition for more than 3 billion people – grows in standing water. But like other plants, it will die if it remains submerged too long. Scientists with the International Rice Research Institute in the Philippines and with two University of California campuses isolated a rice gene, Sub1A, that governs the way plants respond to key hormones that, in turn, govern the plant's survival when submerged.

When the gene is "over-expressed," the plants respond more readily to these hormones, boosting their survival.

Instead of dying within a week of submergence, the altered rice survived from 10 to 14 days. This could benefit growers in two ways, researchers say. Crops would be protected from many floods. And growers could use less herbicides by keeping their fields flooded longer to suppress weeds. The team added the gene to a strain of rice grown in India and found that, in addition to flood survival, the gene boosted yields as well.

The results appeared in the Aug. 10 issue of the journal Nature.

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