Feeling the heat in Hawaii – climate change and the pacific decadal oscillation

A new paper published in Geophysical Research Letters sheds some interesting light on the impacts of climate change and regional shifts in temperature. Whilst it’s generally accepted that the instrumental temperature record shows an upward trend (see here for a graph), the regional patterns of climate change are less well known. Through analysis of an 85 year dataset of 21 base stations across the Hawaiian Islands, Giambelluca and his team from the University of Hawai’i show a dramatic increase in temperature trends over the past 30 years, with a stronger trend in the high altitude regions. According to their data, most of this warming is attributed to increases in minimum temperatures rather than the maxima, resulting in a decrease in the diurnal range of temperatures:


At a glance, it’s easy to ‘eyeball’ this graph and consider it a skeptical field day. After all, according to the data the temperature was warmer in the 1940’s than throughout the last two decades, right? Even more alarming: for the majority of the dataset, the temperature cycles have followed the pacific decadal oscillation (PDO, a natural pattern of climate variability in the pacific on a 20-30 year cycle). The long-term trends of the PDO look like follow a trend as follows:


The recent Hawaii data set suggests that although the PDO is currently in a ‘cool’ phase, climate change has effectively ‘derailed’ the PDO cycle, as evident in the increase in linear trends of temperatures from 1975 onwards. Such changes on a regional scale are a huge cause for concern, particularly in the high altitude areas of Hawaii such as Mauna Kea (the worlds tallest mountain when measured from the base of the Pacific Ocean), which has a high rate of endangered endemic flora and fauna.