Scientists are warning that an Antarctic ice shelf the size of Northern Ireland is on the verge of disintegration, even though it is now the middle of the southern hemisphere's winter.

The European Space Agency says new satellite pictures show that the Wilkins shelf – the largest to be threatened so far – is "hanging by its last thread". Extending for approximately 5,600 square miles, it has been held in place by a thin ice bridge connecting it to an island, but this is now fracturing.

The shelf, which lies near the base of the Antarctic Peninsula, had not been expected to collapse until the early 2020s. It provides further evidence that the planet is warming more quickly than predicted.

Download the new Independent Premium app Sharing the full story, not just the headlines

Scientists are stunned that it is continuing to melt in the depths of winter, and believe that warm water is welling up from the ocean to attack it from underneath. So far seven shelves on the peninsula have collapsed due to climate change.

On Friday, President Bush – who last week told the G8 summit "Goodbye from the world's greatest polluter" – defied a 2007 ruling by the US Supreme Court to take action on global warming under the Clean Air Act.