This has already been posted in the blogosphere recently, so I will put it out here for comment:

The supposedly already-degraded state of coral reef ecosystems is sometimes claimed to be a reason why anthropogenic global warming will have a major impact on the reefs, i.e. they are already close to extinction and can easily be tipped over the edge.

A recent paper** by Peter Ridd challenges the methodology used to conclude that the outer and inner Great Barrier Reef (GBR) are already 28% and 36% respectively, down the path towards ecological extinction.

**A CRITIQUE OF A METHOD TO DETERMINE LONG-TERM DECLINE OF CORAL REEF ECOSYSTEMS
by Peter V. Ridd. Reprinted from ENERGY & ENVIRONMENT, VOLUME 18 No. 6 2007

The full article is archived here.