As the planet warms, giant icebergs and sea ice that once would have remained trapped in the frozen Arctic are moving southward faster and more frequently, menacing shipping and oil and gas drilling operations.

In the North Atlantic, scientists say the number of icebergs spotted south of 48 degrees latitude—where they start to get into more shipping lanes—is up again this year, following a series of extreme iceberg seasons.

“So far, iceberg numbers crossing south of 48 degrees look to be higher this year than last, and last year saw a relatively high iceberg flux year—about 1,000 icebergs crossing 48 North, compared to the long-term mean of 450,” said University of Sheffield geographer Grant Bigg, who studies icebergs and climate.

That ice can pose serious risks to ships and offshore oil and gas rigs. Last year, strong storms sent a swarm of icebergs surging into the oil and gas drilling field at the Grand Banks off Newfoundland, marking the fourth extreme iceberg season in a row, according to International Ice Patrol Commander Gabrielle McGrath.

“There were so many in the area that we couldn’t count them all. Our models couldn’t keep up with how quickly they were moving to the south,” she said.

During one week, the number of icebergs in McGrath’s watch area in the North Atlantic surged from 37 to 455. At the peak of the iceberg invasion, the trackers also found seven icebergs outside their normal monitoring area, creating what McGrath described as the most dangerous possible situation for North Atlantic mariners.

“The oil and gas industry on the Grand Banks was inundated,” McGrath said. “There were so many icebergs coming on to the rigs that they couldn’t keep up. They do towing operations a lot of times, where they lasso the icebergs and pull them away, but they couldn’t get that into place, so they were using water cannons standing on rigs and boats to push them away because they were coming on to the rigs so fast.” 

The same spring storms pushed massive amounts of Arctic sea ice toward the Canadian coast, where it persisted through July, trapping fishing boats and cutting off ferry service.

Scientists working in Newfoundland at the time tested the ice and were surprised to find giant ice floes that had drifted more than 1,800 miles from north of Greenland in a single season. Some of the ice floes were more than 300 feet wide, pressed together in a sea of frozen slush and studded with icebergs up to 50 feet high.

Another Warm Winter Raises the Risks

This past winter, persistent heat waves returned to the Arctic. Scientists tracked a huge area of open water north of Greenland where the thickest ice typically would be. Around the same time, there was open water north of Svalbard, in the European Arctic, and off the North Coast of Alaska—extreme conditions caused by climate change across the Arctic. When the spread of Arctic sea ice reached its peak for the winter on March 17, it was at its secound-lowest maximum extent on record.

Increased ice mobility is a sign that the Arctic climate system is likely to change in big increments in the next few decades, said University of Manitoba ice researcher Dave Babb, one of scientists who tested the sea ice off Newfoundland last year.

The sea ice pack is becoming mechanically weaker, Babb and his colleagues wrote in a new study describing their findings in the scientific journal Geophysical Research Letters. Solid ice structures that once blocked the narrow Arctic Ocean channels and kept the ice pack bottled up are forming later in the winter as global temperatures rise, letting massive slabs of sea ice, some up to 20-feet thick, move south faster than ever before, they said.

Babb was on his way to Hudson Bay aboard the Canadian Coastguard icebreaker Amundsen when the ship encountered the unusual ice jam off the coast of Newfoundland.

In between assisting with rescues or guiding passenger and cargo ferries through the floes, the scientists on board the ship took measurements of the dense ice pack, including chemical fingerprints that show how old the ice is and where it came from.

The drifting sea ice was also studded with thousands of icebergs, most of them from Greenland’s accelerating glaciers. Those rivers of ice have speeded up sharply in recent years, and the icebergs that break off of them into the ocean drift southward, where they get caught up in the drifting sea ice. The past two decades have seen the highest number of icebergs in the northwest Atlantic since at least 1900.

The pattern could persist for at least several decades, but the long-term future for icebergs is less certain, because some glaciers will retreat so far inland that they won’t be able to discharge icebergs into the ocean anymore. Instead, the glaciers will terminate on land and release the melting ice as water, Bigg said.

Heightened Risks for Drilling?

Emerging sea ice hazards are also important in the context of proposals for more offshore oil and gas drilling in the Arctic.

“The ice is acting very strange all over the Arctic,” said Greenpeace researcher Tim Donaghy, whose group has been focusing on the Chukchi Sea and Beaufort Sea, off Alaska, where there are active drilling proposals.

The Arctic Ocean along the northern coast of Alaska is remaining unfrozen for more than two months longer than just 30 years ago, and there’s evidence that storms are getting stronger over the open water, and whipping up bigger waves.

The extreme conditions would make cleaning up an oil spill nearly impossible, Donaghy said.

“The general story of the oil industry is that the easy stuff is already gone. They are pushing into more extreme areas, and the Arctic has been the frontier,” he said. “The arctic is melting because of our reliance on oil, yet we’re drilling for more of it. It’s vicious feedback cycle that’s not going to end well.”