Shipping and resource exploration are expanding into hitherto rarely used areas of the Arctic and the Southern Ocean while, at the same time, iceberg discharge is increasing due to global warming – warns Professor Grant Bigg

At 11.40pm local time on the cold, moonless, night of April 14, 1912, near 41o47’N, 49o55’W – the crow’s nest lookouts on board the Titanic sighted a large iceberg only 500 metres ahead. Despite quick action on the bridge to slow the ship and turn to port as well as the closing of the watertight doors, the slow response of a large vessel meant that the iceberg still struck the ship aft of the bows. Some 100 metres of her hull below the waterline buckled, allowing water to flood into the ship across several compartments. In little more than two and a half hours, she had sunk with the loss of 1,514 lives. Was the iceberg risk greater in 1912 than today?

In 1912, ice warnings largely relied on information exchanged between ships at sea. Today there is an extensive ice hazard warning service in the North Atlantic, provided by the International Ice Patrol and a number of commercial and government ice or weather services. These modern services rely on a combination of sightings, satellite imagery, radar and iceberg models. The services attempt to cover the Southern Ocean and the Arctic during summer but often with less accurate data and no predictive modelling.

These warning services have led to a dramatic drop in the number of iceberg-ship collisions since 1913. However, accidents and indeed sinkings still occur. A well-known recent example was the sinking of the cruise ship MV Explorer in 2007 after a collision with an iceberg in the Weddell Sea, off Antarctica. But better monitoring is not the only factor involved in risk reduction. The number of icebergs flowing into shipping lanes is also important: the more icebergs that calve, the more likely that some will escape monitoring or that human error can operate during iceberg-ship close encounters.

During the first fortnight of April 1912 before the Titanic tragedy, a number of reports of ice were exchanged between ships in the North West Atlantic. A lot of icebergs and sea-ice was present in the shipping lanes crossing the Labrador Sea, off Newfoundland and the Atlantic seaboard. This has led to theories linking exceptional iceberg numbers in 1912 to effects like sunspots or extreme tides on the coast of Greenland. Our recent research, however, using the iceberg records of the International Ice Patrol and an iceberg-ocean model suggests that view needs revisiting.

Following the Titanic disaster, the International Ice Patrol was established to monitor ice hazard and warn shipping in the North West Atlantic. One way they quantify the iceberg hazard is by reporting the number of icebergs seen south of 48oN, a latitude extending out into the Atlantic from the south of Newfoundland. This recording has continued ever since 1913, and using earlier ship reports the series reaches back to 1900. In 1912, 1,038 icebergs were reported crossing this latitude circle.

In a record that varies between 0 and over 2200 icebergs a year, this is a significant number but there are several years in surrounding decades with similar numbers and many years since the mid-1970s have exceeded this number, often significantly. Over 1,200 were recorded in 2009 and this year already looks to be a significant ice year, for example. The iceberg risk, in terms of numbers, in 1912 then was significant but not unprecedented and has arguably been greater in recent decades.

Our ocean-iceberg modelling suggests the Titanic iceberg originated from southwest Greenland, calving in the late summer or autumn of 1911 and flowing across the Labrador Sea, rather than being caught in the circulation system further north, in Baffin Bay. Our research also suggests that what causes mean calving numbers to fluctuate from decade to decade is climate variability. This can be in terms of the amount of melting on the Greenland ice cap, where greater melting destabilises glaciers or the ocean temperature where higher temperatures act in a similar fashion, but underneath calving margins. These effects vary in time, although what has changed significantly in recent decades is the increase in importance of both factors as global warming has developed.

There are very good ice warning services today and the technology to detect and track icebergs constantly develops. However, shipping and resource exploration are expanding into hitherto rarely used areas of the Arctic and the Southern Ocean. At the same time, iceberg discharge is increasing – not every year but there are heavier iceberg years since the 1980s than before – and increasing global warming will likely cause this trend to continue. Icebergs will remain a very real risk for years to come.

Grant Bigg is professor of earth systems science at Sheffield University, in the United Kingdom