Sunday, September 11, 2016

The Still-Icy Arctic Ocean

Years ago I predicted this would be the month that Arctic Ocean would have so little ice that ordinary cargo ships could pass through the middle of it. That didn’t happen, but this summer’s melting shows that favorable weather won’t save the sea ice from the effects of global warming.

Arctic sea ice is a fraction of what it was when detailed record-keeping started in 1979, and that is what led me to predict a substantially ice-free late summer. At the same time, it seemed there was reason to hope that a run of good luck with the weather might allow Arctic ice to hang on in a semblance of its current form for another decade. That would require quiet spring weather, clouds in June and July, and light winds so that there is hardly any outflow. That last point seemed the most important. Surely, with less and less ice as the years go by, it would get harder and harder for winds to push the ice out of the Arctic and into the Atlantic.

This year was a good test of that idea. April through mid-August provided almost the best weather patterns we could imagine for the ice. Outflow virtually stopped from April until the end of August. Ice nevertheless tracked near record lows all year long. It is now lower than the September lows of every year but 2012. The answer, then, is that near-ideal summer weather might prevent a new record low for Arctic ice, but it won’t stop the downward trend.

How is this possible? Global temperatures seem the most likely culprit. July was the warmest month on record globally, and for the last three years, more months than not have set new high temperature records for the world. Though we can’t pin down how it happens, it seems that some of the warmth is making its way from the Pacific Ocean to the Arctic Ocean. Some observers think the Atlantic Ocean must be warmer than before and transporting more heat into the areas where it borders on the Arctic Ocean. There aren’t thermometers all over the Arctic region, so these are just guesses, but they seem more likely than not.

The weaker, more fragmented Arctic ice is also a problem. So far this month, winds have been pushing ice not into the Atlantic, but into Canada. But instead of jamming up in the narrow straits as in past years, the ice is flowing through freely and melting before it reaches the mainland. In floes mostly smaller than a kilometer, the broken ice looks and acts like a fluid when observed from satellites. When the wind blows in other directions, ice may end up moving in the general direction of the Bering Strait and the Pacific Ocean. This area too used to be a safe haven where ice could survive for years, but on today’s map, only a few rapidly shrinking ice islands remain. As one observer put it, no matter which way the wind blows, it is bad for the ice.

The only weather that will save the ice in summer, it seems, is light winds and lots of clouds, but that’s a lot to ask for. Those are conditions that result from low pressure, but the pressure can’t get so low that it creates a storm and the winds start blowing. Persistent conditions of medium-low pressure don’t happen often. Nevertheless, those were the weather conditions of June and July this summer in the central Arctic, and the ice kept melting. Good weather is not enough. Only a cooler planet will save the Arctic sea ice from its downward spiral, and realistically, there are no plans to stop the current global warming trend.

If I were on an ordinary cargo ship crossing the Arctic Ocean, I wouldn’t want to see ice. I would want an ice-free passage 100 kilometers wide to travel through. But to a ship with a reinforced hull, thin ice is almost the same as open water. Early in the summer, two U.S. military ships on research missions approached the North Pole without any special difficulty — and that was when the ice was twice as thick as it is now. An Arctic-class cargo ship probably could pass through the weakest ice of the central Arctic, roughly along the 45° and 165° East meridians. I hope no ship is attempting this, though. The Northwest Passage and Northern Sea Route have both been open for cargo for the past month. Weeks ago, a large cruise ship traversed the Northwest Passage without incident, the first time that’s been attempted. With two routes offering logistical support, who would be the first to attempt a shortcut through an unsupported route that is almost 50 percent ice?

Still, this month is the first time that the phrase “probably possible” has been applied to the Central Arctic Route. That puts the Central Arctic Route barely a decade behind the Northern Sea Route, a route that the cargo industry now takes for granted. If the world keeps warming, it may take little more than a mild winter and a sunny summer to open the Central Arctic Route to shipping.