Southwest Pacific temperatures: Diurnal and seasonal trends

Temperature trends are presented for a large part of the southwest Pacific. The trends differ from those documented for Northern Hemisphere land areas, where warming has occurred mainly through increases in minimum temperature. The New Zealand patterns are derived from recently completed analyses of monthly and annual mean maximum and minimum surface temperature records for a newly homogenised historical climate data series for New Zealand and outlying islands. They indicate that the warming in the New Zealand region over the past five decades can be attributed to increases in both mean maximum (mostly daytime) and mean minimum (mostly night time) temperature. All seasons show a temperature increase, with the largest occurring in summer (DJF). Northern Hemisphere evidence suggests that changes in cloud cover and the presence of sulfate aerosols plays a direct role. The present results imply that, while the observed warming in a large portion of the Northern Hemisphere landmass may be significantly affected by both these factors, sulfate aerosol effects may be less important in the Southern Hemisphere.