Trends and Variations in South Pacific Island and Ocean Surface Temperatures

Abstract

An analysis of temperature variability and trends in the South Pacific, mainly in the twentieth century, using data from 40 island stations and optimally interpolated sea surface and night marine air temperature data is presented. The last-named dataset is new and contains improved corrections for changes in the height of thermometer screens as ships have become larger. It is shown that the South Pacific convergence zone plays a pivotal role in both variability and trends in all three datasets. Island, collocated sea surface temperature, and night marine air temperature time series for four large constituent regions are created and analyzed. These have been corrected for artificial changes in variance due to changes in the availability of constituent island stations whose intrinsic variance varies from station to station. The method is described in detail. Objective estimates of uncertainty in the sea surface temperature data are also provided. The results extend previous work, showing that annual and seasonal surface ocean and island air temperatures have increased throughout the South Pacific. Variations in trends in the island and marine data show reasonable consistency, with distinctly different patterns of multidecadal change in the four regions. However, a notable inconsistency is the recent lack of warming in night marine air temperature in one of the tropical regions relative to sea surface temperature, with signs of this effect in a second tropical region. Another tropical region near the South Pacific convergence zone shows recent strong warming in the island data but not in the marine data.