Read here. All scientists agree that during the Holocene, global temperatures were significantly warmer some 7,000 to 9,000 years ago. This warm climate meant sea temperatures were also warmer, which allowed coral reefs to grow to immense sizes, plus expand into the mid-latitudes, where they currently don't exist.
New peer-reviewed research by Woodroffe et al., based on the historical Holocene evidence record, suggests that coral reefs will respond favorably to any future global warming conditions.
"The nine researchers discovered an extensive relict coral reef around Lord Howe Island in water depths of 25-50 meters, which flourished in early Holocene times about 9000 to 7000 years ago, which they describe as "immense," as it was "more than twenty times the area" of the modern reef at that site.....say their finding "demonstrates that reefs were much more extensive 9000 years ago than they are at present at this latitudinal limit to reef growth," and they conclude that the "relict reef, with localized re-establishment of corals in the past three millennia, could become a substrate for reef expansion in response to warmer temperatures, anticipated later this century and beyond.""....."Hence, they opine that these and other similar sites "may represent important refugia from increases in sea surface temperature," ". [Woodroffe, C.D., Brooke, B.P., Linklater, M., Kennedy, D.M., Jones, B.G., Buchanan, C., Mleczko, R., Hua, Q. and Zhao, J.-X. 2010: Geophysical Research Letters]
Additional peer-reviewed postings and other coral reef postings.