On land, the "equivalent would be tropical forests turning white ... and then dying," said Richard Vevers, executive director of XL Catlin Seaview Survey, which also contributed to the report.
"The last two events have gone virtually unnoticed," he told Reuters of the bleachings in 2010 and 1998.
The University of Queensland and Reef Check were also involved in the surveys.
Mr Eakin said countries could help by reducing stresses on reefs such as over-fishing and pollution.
Nearly 200 governments will meet in Paris from Nov 30 to Dec 11 to address the wider problem of climate change.