Half northern Great Barrier Reef will die

More than half the northern part of the Great Barrier Reef is dead or dying due to severe coral bleaching, a Senate committee has been told.

Great Barrier Reef Marine Park Authority chairman Russell Reichelt said surveys showed about 50 to 60 per cent of the 900 reefs in the northern section of the heritage site have or would die.

"It's very strongly linked to global warming," Dr Reichelt told a Senate estimates committee on Thursday, warning climate change was the biggest risk to the reef.