An estimated 75 per cent of the world's coral reefs are threatened by local human activity, including over-fishing, coastal development and pollution, and global pressures such as climate change, warming seas and rising ocean acidification, according to a United Nations-backed report unveiled Thursday.

"Reefs at Risk Revisited," launched in Washington and London, says that if the threats to the reefs are not dealt with, more than 90 per cent of them will be threatened by 2030 and nearly all reefs will be at risk by 2050.

Global pressures are leading to coral bleaching from rising sea temperatures and increasing ocean acidification from carbon dioxide pollution, according to the assessment of threat to coral reefs by the World Resources Institute, the Nature Conservancy, the WorldFish Center, the International Coral Reef Action Network, the Global Coral Reef Monitoring Network and the World Conservation Monitoring Centre of the UN Environment Programme (UNEP-WCMC), along with a network of more than 25 organizations.

"This report serves as a wake-up call for policy-makers, business leaders, ocean managers and others about the urgent need for greater protection for coral reefs," said Jane Lubchenco, Under-Secretary of Commerce for Oceans and Atmosphere and Administrator of the US National Oceans and Atmospheric Administration (NOAA).

"As the report makes clear, 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," she added.

According to Lauretta Burke, senior associate at the World Resources Institute and a lead author of the report, coral reefs are valuable resources for millions of people worldwide.

"Despite the dire situation for many reefs, there is reason for hope," she said. "Reefs are resilient, and by reducing the local pressures we can buy time as we find global solutions to preserve reefs for future generations."

The report includes multiple recommendations to better protect and manage reefs, including through marine protected areas. The analysis shows that more than one-quarter of reefs are already encompassed in a range of parks and reserves, more than any other marine habitat. However, only 6 per cent of reefs are in protected areas that are effectively managed.

"Well-managed marine protected areas are one of the best tools to safeguard reefs," said Mark Spalding, senior marine scientist at the Nature Conservancy and one of the authors.

"At their core, reefs are about people as well as nature: ensuring stable food supplies, promoting recovery from coral bleaching, and acting as a magnet for tourist dollars. We need to apply the knowledge we have to shore up existing protected areas, as well as to designate new sites where threats are highest, such as the populous hearts of the Caribbean, South-East Asia, East Africa and the Middle East," he added.

According the report, more than 275 million people live in the direct vicinity of coral reefs. In more than 100 countries and territories, coral reefs protect 150,000 kilometres of shorelines, helping defend coastal communities and infrastructure against storms and erosion.

The report identifies the 27 nations most socially and economically vulnerable to coral reef degradation and loss. Among these, the nine most vulnerable countries are Haiti, Grenada, Philippines, Comoros, Vanuatu, Tanzania, Kiribati, Fiji and Indonesia.