About the sea surface temperature trend maps

Analyses available

Annual and seasonal mean sea surface temperature (SST) trend maps are available for the Australian region for periods starting at the beginning of each decade from 1900 to 1970 to near present. Analysis periods starting after 1970 are considered to be too short to calculate meaningful trend values.

Interpreting the analyses

The trend maps are a useful way to compare how the sea surface temperature has changed in different regions around Australia over time. However, they need to be interpreted with caution. Trend values have been determined from a linear (straight line) fit to the data, but the change indicated may not have been gradual. For example, a calculated trend could be due to a relatively rapid "step" change, with the remainder of the series being fairly flat. A representation of the temporal evolution of surface temperature changes is shown in the corresponding be the timeseries graphs.

Very recent observations have not been subjected to the same degree of quality control as past data. Users are advised to keep in mind the period over which trend values have been calculated and interpret them alongside the timeseries of spatially averaged values.

The trend values calculated here using past observations, should not be used to imply future rates of change. Due to the complex interactions between the natural and anthropogenic drivers of ocean temperatures, the sea surface temperature of any location is always changing. Future rates of change will depend on how these drivers interact in future, which will not necessarily be the same as in the past.

Finally, the data used here are based upon historic instrumental observations and do not include any satellite data. Trend maps are based upon underlying 2 degree observations grids which have been interpolated near coastlines.

Mean sea surface temperature values are provided for a boxed region around Australia (from 4°S to 46°S and from 94°E to 174°E), as well as for six regions within this box: the Northern Tropics (4°S–22°S, 94°E–174°E), the Southern Region (30°S–46°S, 94°E–174°E), the Southwest Region (22°S–46°S, 94°E–116°E), the Northwest Region (4°S–22°S, 94°E–130°E), the Coral Sea (4°S–26°S, 142°E–174°E) and the Tasman Sea (26°S–46°S, 150°E–174°E).

These regions are the same as those used to provide timeseries on these pages.

Trend maps are provided for the seven regions shown above

The above areas have been chosen for analysis since they are large enough to contain a meaningful climatology and not be influenced by data and interpolation errors. At the same time, these areas are small enough to provide a meaningful representation of regional climate influences around the Australian continent.

Data used

The sea surface temperature trendmaps are calculated from the NOAA Extended Reconstructed Sea Surface Temperature Version 5 (ERSST v5) data provided by the NOAA/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/. A full description of the ERSST v5 data can be found in Huang et al., (2017), with the earlier ERSST v4 described in Huang et al., (2015) and Liu et al., (2015).

Since November 2016, the ERSST v5 dataset is impacted by the reduction of the number of drifting buoy reports into the ICOADS Near-Real-Time product (R3.0.1). This is noted on the NOAA ICOADS website. The impact on ERSST v5 is expected to be minimal as the dataset incorporates a number of other observation datasets.

Please note that any use of the data analysed on these web pages should be acknowledged to the Bureau of Meteorology. Apart from the purposes of study, research, criticism and review, no part of these data may be reproduced, or redistributed for any commercial purposes, or distributed to a third party for such purpose, without written permission from the Director of Meteorology.

Further information

Huang, B., P.W. Thorne, V.F. Banzon, T. Boyer, G. Chepurin, J. Lawrimore, M.J. Menne, T.M. Smith, R.S. Vose and H.-M. Zhang, 2017: Extended Reconstructed Sea Surface Temperature version 5 (ERSST.v5): Upgrades, validations and intercomparisons. Journal of Climate doi:10.1175/JCLI-D-16-0836.1

Huang, B., V.F. Banzon, E. Freeman, J. Lawrimore, W. Liu, T.C. Peterson, T.M. Smith, P.W. Thorne, S.D. Woodruff, and H.-M. Zhang, 2015: Extended Reconstructed Sea Surface Temperature version 4 (ERSST.v4): Part I. Upgrades and intercomparisons. Journal of Climate, in press, doi:10.1175/JCLI-D-14-00006.1

Liu, W., B. Huang, P.W. Thorne, V.F. Banzon, H.-M. Zhang, E. Freeman, J. Lawrimore, T.C. Peterson, T.M. Smith, and S.D. Woodruff, 2015: Extended Reconstructed Sea Surface Temperature version 4 (ERSST.v4): Part II. Parametric and structural uncertainty estimations. Journal of Climate, in press, doi:10.1175/JCLI-D-14-00007.1