Scientists at the National Oceanic and Atmospheric Administration (NOAA) warn that warm ocean temperatures in the tropical Pacific and Indian Oceans could trigger major coral bleaching events across the globe in 2015.

At worst, the bleaching events might bring about a disastrous third global coral bleaching event this year.

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The most recent outlook from NOAA's weekly Coral Reef Watch report shows the greatest threat for coral bleaching through May 2015 is in the western South Pacific and Indian oceans.

In the Pacific, thermal stress has already reached levels that cause bleaching in the nations of Nauru, Kiribati, and the Solomon Islands. This is expected to spread to Tuvalu, Samoa, and American Samoa in the next few months.

In the Indian Ocean, thermal stress may reach levels that cause bleaching around Madagascar, Mauritius, Seychelles, and parts of Indonesia and Western Australia. NOAA said its scientists in American Samoa are already seeing the start of bleaching on their shallow reefs.

"In the coming months, we will be watching to see if the model predicts conditions that can cause bleaching in Southeast Asia and the Coral Triangle region around mid-2015," said said Mark Eakin, NOAA Coral Reef Watch coordinator.

"The outlook shows a pattern over the next four months that is similar to what we saw during global coral bleaching events in 1998 and 2010. We're really concerned that 2015 may bring the third global coral bleaching event", Eakin noted.

Coral bleaching simply means a mass die-off of corals. Dead corals lose their lively, bright colors created by the symbiotic algae living in their tissues and turn a sickening grayish white in color.

Coral bleaching takes place when corals are stressed by changes in conditions such as temperature, light or nutrients. Because of warmer waters, corals expel the symbiotic algae, causing them to turn white or pale. Without the algae, the coral loses its major source of food and is more susceptible to disease.

Coral reefs make up less than one percent of Earth's undersea ecosystems, but shelter 25 percent of marine species; protect shorelines; support fishing industries and bring in tourist dollars.

"Climate change and its impacts, which can include bleaching, are some of the most pressing global threats to coral reef ecosystems today," said Jennifer Koss, acting program manager for NOAA's Coral Reef Conservation Program.

"This suite of products is vital to help scientists, coral reef managers, and decision makers in the U.S. and around the globe prepare for bleaching events."