Monitoring a changing climate for coral reef ecosystems over the next few decades – Signals from the past 25 years

The NOAA/NASA Pathfinder sea surface temperature (SST) data from 1985 to 2008 are examined for variability and trends and compared with NOAA/NESDIS' operational SSTs for implications on the near future of global tropical ecosystems. These twenty-four years of satellite observations reveal some noteworthy shifts that have quite different implications for each major ocean basin, in addition to revealing expected increasing trends toward higher latitudes especially in the northern hemisphere, confirming the Intergovernmental Panel on Climate Change (IPCC) projections. Although global SST trends throughout the tropics show several regions experiencing decreasing SSTs over the 24-year timeframe, most regions are showing rising trends. Most notable and worrisome is an obvious shift after the recent PDO reversal from cooling to warming over certain tropical waters. While a brief stabilization of upward trends during the past decade might look hopeful, the past 10 years' average data show the highest SSTs over the tropics to date.

We also examine trends of coral bleaching “HotSpots” and “Degree Heating Weeks” that serve as indices for the occurrence, intensity and duration of thermal stress causing coral bleaching. Increased thermal stress has been contributing significantly to the degradation of the world's coral reef ecosystems during the past few decades. Regionally, those coral reefs experiencing troubling upwards trends in SSTs, including elevated HotSpot and Degree Heating Weeks over the past decade, are in the Caribbean and Mid-Pacific. What will be instructive for the future of our planet's precious coral reef ecosystems is whether the recent stabilization in trends continues over the global tropical ocean since the recent PDO reversal.