A major new assessment says that three-quarters of the world’s coral reefs are at risk due to overfishing, pollution, climate change and other factors.

Researchers say that the biggest threat is exploitative fishing, though most reefs will be feeling the impact of climate change within 20 years.

The report is compiled by a group of more than 20 research and conservation organisations, led by the World Resources Institute (WRI) in Washington DC.

“Local and global threats, including climate change, are already having significant impacts on coral reefs, putting the future of these beautiful and valuable ecosystems at risk,” the BBC quoted Jane Lubchenco, head of the U.S. National Oceanic and Atmospheric Agency (Noaa), as saying.

The report revisits some of the territory explored in the original Reefs at Risk project, published in 1998, but in much greater detail.

Over the 13 years intervening, the area at risk of destruction has increased by nearly a third.

The main reason for that change has been a massive increase in damage from exploitative fishing, particularly in the Indian and Pacific Oceans.

Other major threats are pollution carried in rivers, coastal development, and climate change.

If climate projections turn into reality, then by 2030 roughly half of the world’s reefs will experience bleaching in most years - rising to 95 p.c. during the 2050s.