A23a: Giant iceberg on collision course with island

The world’s largest iceberg is on a collision course with a remote British island, potentially putting penguins and seals in danger.

The iceberg is spinning northwards from Antarctica towards South Georgia, a rugged British territory and wildlife haven, where it could ground and smash into pieces. It is currently 173 miles (280km) away.

Countless birds and seals died on South Georgia’s icy coves and beaches when past giant icebergs stopped them feeding.

“Icebergs are inherently dangerous. I would be extraordinarily happy if it just completely missed us,” sea captain Simon Wallace tells BBC News, speaking from the South Georgia government vessel Pharos.

Around the world a group of scientists, sailors and fishermen are anxiously checking satellite pictures to monitor the daily movements of this queen of icebergs.

It is known as A23a and is one of the world’s oldest.

It calved, or broke off, from the Filchner Ice Shelf in Antarctica in 1986 but got stuck on the seafloor and then trapped in an ocean vortex.

Finally, in December, it broke free and is now on its final journey, speeding into oblivion.

The warmer waters north of Antarctica are melting and weakening its vast sides that extend up to 1,312ft (400m), taller than the Shard in London.

It once measured 3,900 sq km, but the latest satellite pictures show it is slowly decaying. It is now around 3,500 sq km, roughly the size of the English county of Cornwall.

And large slabs of ice are breaking off, plunging into the waters around its edges.

A23a could break into vast segments any day, which may then hang around for years, like floating cities of ice cruising uncontrollably around South Georgia.

All three men describe a rapidly changing environment, with glacial retreat visible year-to-year, and volatile levels of sea ice.

Climate change is unlikely to have been behind the birth of A23a because it calved so long ago, before much of the impacts of rising temperatures that we are now seeing.

But giant icebergs are part of our future. As Antarctica becomes more unstable with warmer ocean and air temperatures, more vast pieces of the ice sheets will break away.