Whether or not you recognize the causes of climate change, some effects are becoming indisputable. The latest: coral reefs all over the world are dying due to heat stress.

According to a new study by the United Nations Educational, Scientific and Cultural Organization (UNESCO), the World Heritage coral reefs are in danger of dying out completely by 2040 unless carbon emissions are reduced enough to slow the ocean warming. The new study, the first global examination of reefs over the entire planet, found that of the 29 World Heritage reef areas, at least 25 will experience severe bleaching events by 2040.

"Seeing the damage being wrought has just been heartbreaking," says reef expert Mark Eakin with the NOAA, a lead author of the report. By 2100, most reef systems will die unless carbon emissions are reduced. "Warming is projected to exceed the ability of reefs to survive within one to three decades for the majority of the World Heritage sites containing coral reefs."

Humans and animals alike depend on coral reefs for food and shelter. Although they occupy less than 1% of the ocean floor, they provide habitat for a million species and protect coastlines against erosion from tropical storms. Ruth Gates, director of the Hawaii Institute of Marine Biology, points to a reduction in food supplies, lack of coastal protection, and land erosion of detrimental consequences to coral bleaching as potential consequences, and says people impacted by these areas will have to move.

Although these are future projections, scientists have seen 25 reefs experience severe bleaching events in the last three years, the most severe sequence of bleachings to date. The Great Barrier Reef was especially impacted, as well as the Seychelles in New Caledonia east of Australia.

"We're seeing truly catastrophic damage to many reef systems around the world," said Eakin. "The Great Barrier Reef damage we've seen is greater than anything we've seen in the past 20 years."

Other consequences of coral bleaching include saltwater inundating freshwater drinking sources in low-lying islands such as Kiribati, a string of islands in the central Pacific Ocean. Loss of coral combined with global overfishing will mean fewer fish and protein shortages for the people who depend on them. "These are real things that real people are experiencing," said study co-author Scott F. Heron.

The solution, says Heron, depends on more people embracing the science of current projects of global warming and coral bleaching, and working to curb greenhouse gas emissions before they severely impact the people who live around these reefs.

"If we don't act there will be many, many serious impacts."