On the horizon

Earth's methane levels level out

Atmospheric methane – a far more potent greenhouse gas than carbon dioxide – has held steady for the past seven years, following 20 years of increases. Scientists making the measurements say the change may result from fewer leaks in pipelines and oil and gas storage facilities. They add that emissions from coal mining and natural-gas production may have been reduced.

The team gathered sea-level air samples from land- and island-based canisters along a rough line from northern Alaska to New Zealand. It's unclear how long the trend might hold. But "we will gain some ground on global warming if methane is not as large a contributor in the future as it has been in the past century," notes F. Sherwood Rowland, a Nobel Prize-winning atmospheric scientist at the University of California at Irvine. He led the team that reported its results in the Nov. 23 issue of Geophysical Research Letters.

In 2000, NASA scientist James Hansen and a colleague argued in a paper in the Proceeding of the National Academies of Science that an immediate focus on curbing less-abundant, but more-potent, greenhouse gases, including methane, could buy time to work out more-effective strategies to reduce carbon-dioxide emissions.

The ancient Greeks knew how to gear up to calculate astronomical events.

A new analysis of fragments from a 2,000-year-old calculator called the Antikythera Mechanism shows that it not only could track the motions of the planets, but it could also duplicate the movements of the moon, based on a complex theory of the moon's motions attributed to mathematician and astronomer Hipparchos (ca. 190-125 BCE).

The machine's fragments were recovered in 1901 from an ancient Roman shipwreck. British, Greek, and US scientists used detailed visual and X-ray images to decipher inscriptions and figure out how the system of gears functioned.

The machine, built sometime between 150 and 100 BCE, reveals "an unexpected degree of technical sophistication for the period," the team writes in the current issue of the journal Nature. It was more complex "than any known device for at least a millennium afterwards."

Scientists have seen how violent volcanic eruptions in the tropics have produced warmer winters far to the north. Now, researchers have shown that eruptions in the north can heat things – and cool them down – near the equator as well.

A team of US and British scientists chose a series of eruptions in Iceland in 1783 as its test case. The eruptions launched more than 100 million tons of sulfur dioxide and other noxious gases into the atmosphere. Following the eruptions, much of northern Africa endured a severe drought. Low water flow along the Nile triggered a famine that reduced the river valley's population by 17 percent. Summer temperatures farther north hit their lowest averages in 500 years.

Using a climate model at NASA's Goddard Institute for Space Science in New York, the team found that changes in air temperature patterns over land and ocean reduced the annual monsoons that bring rain to southern Asia and northern Africa. It's the first time researchers have detected a link between water resources in northern Africa and volcanic eruptions much farther north.

"Our findings may help us improve predictions of climate response following the next strong high-latitude eruption," notes Luke Oman, a Rutgers University scientist who led the team. The results appear in the Sept. 23 issue of Geophysical Research Letters.