A comparison of annual South Pacific island and ocean surface temperatures
We compare annual air temperatures from South Pacific Islands with surrounding sea surface (SST) and night marine air temperature (NMAT) data over an area of about 21 million km2 using recently improved marine datasets. Sub-decadal and multidecadal (trend) time scales are highlighted and we include tests of the SST bias correction method of Folland and Parker (1995). A major finding is a narrow zone of low correlation between SST and NMAT near the South Pacific Convergence Zone (SPCZ). Here there are locally poor or even negative correlations between island temperatures and adjacent SST. This behaviour is partly due to low interannual variance in this region. In addition, some island temperatures are poorly correlated with adjacent SST or NMAT, being much better correlated with marine temperatures some distance away. When the South Pacific area is divided into four large zones, and seven islands in the SPCZ region are rejected because they show spatially coherent correlation maxima with distant rather than adjacent marine data, sub-decadal variability and trends in island temperature and corrected SST agree quite well. North east of the SPCZ, marine and island temperatures have little trend, or a reduction, until near 1970 and then show a rising trend. Two regions near the SPCZ have trends that are more complex (or sometimes absent) with a fairly low agreement between trends in the three types of temperature data in one region but mostly good agreement in the other. To the south west, an unsteady rising trend is seen since 1900. This appears to have recently slowed and is quite different in character from the behaviour of the zone north east of the SPCZ. The results show that the island and ocean surface temperatures have increased by 0.6 - 0.8°C since 1910 throughout a large part of the South Pacific. Pre-1942 uncorrected tropical SST is too cool relative to island air temperatures, indicating that the relatively large positive bias corrections applied to SST in the tropics have skill. A key conclusion is that the SPCZ represents a major discontinuity in decadal-scale temperature trends within the Southwest Pacific.