Sea Surface Temperature

Observations of Sea Surface Temperature (SST) are essential to understanding the state of the earth’s climate system. SSTs also serve as boundary conditions for numerical weather prediction and other atmospheric model simulations, and as important determinants of marine ecosystems. To these ends, the ocean observing system measures SSTs by deploying temperature sensors on tropical moored buoys, ocean reference stations, and surface drifting buoys, as well as ships of opportunity distributed over the global oceans.

However, even thousands of such in-situ measurements made each day are inadequate to sample temperatures over the vast surface of the ocean; for that purpose, it is necessary to employ the global coverage of space-based measurements of infrared and microwave radiation emitted from the ocean surface, from which sea surface temperature can be inferred. While satellite-based instruments allow us to observe most of the ocean surface with excellent resolution and reproducibility, they lack the absolute accuracy of the in-situ measurements necessary for climate-quality observations. Accordingly, techniques have been developed that combine in-situ measurements with remote observations to extend the broad area coverage available from space to the quality of the relatively sparse but more accurate set of in-situ measurements.

Because of the centrality of SST observations to climate and other endeavors, the Ocean Climate Observation Program sponsors a daily SST product- the NOAA Optimum Interpolation 1/4 Degree Daily Sea Surface Temperature Analysis (OISST). Scientists at the NOAA National Climatic Data Center and the NOAA National Centers for Environmental Prediction produce and freely disseminate SST data on a variety of time and spatial scales.

The subject of how best to derive SSTs from remotely sensed observations remains an active research topic, coordinated internationally by the Group on High Resolution Sea Surface Temperature (GHRSST), whose activities lead to periodic improvements in methodology.

Insofar as the ocean covers 71% of the Earth's surface, knowledge of SSTs is essential to understanding how the surface temperature of the Earth, as a whole, is changing. Although high-precision satellite-based measurements have been available for only a few decades, ocean temperature observations from ships have been cataloged since the 1850s. Scientists at the NOAA National Climatic Data Center have combined modern and historical SST measurements to derive the temperature record of the Earth's sea surface, the Extended Reconstructed Sea Surface Temperature, dating back to 1854. These data, in turn, can be merged with historical land surface data to extend the direct observational history of the Earth's merged land- and ocean surface temperature back to the 19th century.