Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

This indicator was calculated as follows: (1) the seasonal average sea surface temperature (SST) of near-shore water (shoreline out to 25 miles) was calculated for the warmest season in each region (termed the “seasonal mean maximum”), which typically occurred during summer or fall; (2) the long-term mean (during the warmest seasons) for the period of observation (1985–1998) was calculated; and (3) the long-term mean was then subtracted from the seasonal mean maxima. Thus, values greater than zero are positive “anomalies” (i.e., deviations from the long-term average), and those less than zero are negative anomalies.

Because of the large heat capacity of the ocean, changes in water temperature on the scales reported here are likely to reveal universal changes, such as those caused by global warming, sooner than will be apparent in air temperature (i.e., changes in water temperature are less susceptible to daily and seasonal variability). Changes in annual cycles of water temperature and the occurrence of interannual to decadal trends not only will affect the kinds of organisms that will thrive in a region, but are thought to be associated with the degradation of coral reefs (bleaching) and may be related to the development of harmful algal blooms and the growth of invasive species. On longer time scales (decades to centuries), such changes may be related to decreases in the supply of nutrients to surface waters from the deep sea and a cascade of effects from decreases in primary production to declines in fish production.

As discussed in the text, there is considerable evidence building that the surface waters of the oceans are warming gradually (e.g., Barry et al. 1995 and Levitus et al. 2000).

The Data

Data Source: Data from 1985 through 1998 were analyzed for The Heinz Center by the National Ocean Service of the National Oceanographic and Atmospheric Administration (NOAA). The NOAA/National Aeronautics and Space Administration (NASA) Oceans Pathfinder SST data were obtained using Advanced Very High Resolution Radiometers onboard several NOAA Polar Orbiting Environmental Satellites. Complete data are not available for 1996 and 1997, but are available for 1998. It is important to note that SST data are available back to 1979; however, these data are not yet comparable to the series beginning in 1985.

Data Manipulation: Data were acquired on a grid of square pixels nominally 10 km (about 6 miles) on a side. Both the day and nighttime data were processed to remove clouds (using an “erosion filter”) and then averaged to produce monthly means, which were then averaged to produce seasonal means. See “The Indicator” section above for a description of the calculations necessary to generate the SST anomalies.

Data Quality: Systematic errors are rare in such an analysis, and the data are expected to be within 2^oF of actual temperatures measured 3.3 ft below the surface.

Data Availability: Data are available for free on the Web from NASA at http://podaac.jpl.nasa.gov/sst/.

References

Barry, J.P., C.H. Baxter, R.D. Sagarin, and S.E. Gilman. 1995. Climate-related, long-term faunal changes in a California rocky intertidal community. Science 267:672–675.

Levitus, S., J.I. Antonov, T.P. Boyer, and C. Stephens. 2000. Warming of the world ocean. Science 287:2225–2229.