The pack is back. When the National Snow and Ice Data Center in Colorado marked the end of the Arctic ice-melting season in mid-September, 2 million square miles of ice covered the North Pole. That’s a whopping 50 percent increase from a year earlier, when Arctic sea ice set a record low. This year, pack ice was thick enough to block about 20 yachts from sailing the Northwest Passage.

Climate scientists have long pointed to Arctic sea ice extent as a gauge of a warming world. Because ice reflects sunlight into space, decreased pack ice will cause the oceans to absorb more heat, perhaps accelerating a warming trend. In fairness to those warning of climate catastrophe, this year’s Arctic ice bounce back remains below the average for the period between 1981 and 2010. Scientists estimate the North Pole’s ice cover area for 2013 is the sixth smallest since satellite records began in 1979.

But here’s the less noticed headline: Antarctic sea ice set a record in August too—a record high.

While ice cover has decreased in the Arctic, sea ice in the Antarctic has increased about 1 percent per decade since 1979.

The fact is, three decades may not be enough time to accurately measure climate cycles, and we still understand too little about the natural feedbacks built into the climate system. Scientists this year have called it a “puzzle” and a “paradox” that Antarctic ice continues to grow in spite of global warming. They blame the increase on continental meltwater and strong winds.

Our lack of omniscience regarding the climate has led to wildly wrong predictions. In 2007 Wieslaw Maslowski, an oceanographer from the Naval Postgraduate School in Monterey, Calif., used what he believed was a sophisticated “high-resolution regional [climate] model for the Arctic Ocean” to predict the North Pole would be ice-free by summer 2013.

Al Gore cited Maslowski’s prediction six years ago during his Nobel Peace Prize acceptance speech. They were both off by 2 million square miles.

Research roundup

Mars

To the disappointment of sci-fi fans, NASA rover Curiosity has not found evidence of martians. Since landing in August 2012, the rover has measured the atmosphere for methane, a likely signature of microbial life, but failed to find any. Though some microbes on Earth live without emitting methane, the absence of the gas suggests the red rock may be as dead as it looks. (Science)

Immunity

A vaccine to prevent HIV? Oregon researchers have developed a vaccine that appears, for the first time, to have protected nine rhesus monkeys from simian immunodeficiency virus, a cousin of HIV. A version of the vaccine could prevent HIV infections in humans, although potential trials are still a few years away. Also, the researchers need to figure out why their vaccine failed in seven other monkeys. (Nature)

Interstellar space

Voyager 1, one of two nuclear-powered spacecraft launched in 1977, has become the first man-made object to leave the solar system, a team at NASA announced. Their calculations indicate the spacecraft left the solar system’s magnetic field in August 2012. Long outliving its original mission to the planets, Voyager 1 continues to beam back particle data from 12 billion miles away, and should maintain power until about 2025. (Science) —D.J.D.