International shipping lanes in the North Atlantic have almost been ground to a halt by an armada of over 400 icebergs, an increase of 363 in just seven days, once again sounding the alarm about the effects of climate change.

“It makes everything more expensive,” Oceanex executive chairman Captain Sid Hynes said, according to the AP.

“You’re burning more fuel, it’s taking a longer time, and it’s hard on the equipment,” he said, adding that it’s already a “very unusual year.”

Vessels have been forced to slow down dramatically, sometimes to just 3 or 4 knots, while others have had to take evasive action that led to detours of approximately 650km (400 miles), creating delays of over 24 hours, reports the AP.

Climate change has long been blamed for the accelerated melting of the Greenland ice shelf, but this doesn’t explain why the North Atlantic has seen such a substantial ice invasion in such a short space of time.

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Uncharacteristically strong counter-clockwise winds for this time of year could potentially explain the glacial jam, but experts say more analysis is needed.

Iceberg ahead! The International Ice Patrol is vital to assisting vessels find safe, ice-free waters: https://t.co/5RRY23j565#BelowZeropic.twitter.com/UqDSeCuxGe — U.S. Coast Guard (@USCG) February 9, 2017

The icebergs are particularly dense in the area where the Titanic sank in 1912. In the aftermath of the disaster, the International Ice Patrol was founded to protect shipping lanes and avoid a repeat of the tragedy.

US Coast Guard Commander Gabrielle McGrath, leader of the International Ice Patrol, told the AP she had never seen such a massive increase over such a short space of time, adding that she predicted a fourth consecutive “extreme ice season” this year, in which shipping lanes are clogged by 600 icebergs or more.