Future warming rates over the Hawaiian Islands based on elevation‐dependent scaling factors

Abstract

ABSTRACTRegional climate change scenarios are important for understanding their impacts on environments of oceanic islands. This study presents a statistical method that estimates elevation‐dependent warming rates for the Hawaiian Islands. The downscaling is facilitated by two important aspects found in the climate change scenarios produced by general circulation models. First, climate model simulations show a strong relationship between height and amplitude of the temperature change over the northern subtropical Pacific. Second, the ratio between the upper air temperature and the surface temperature change is independent of the global warming rate. This information is exploited to produce high‐resolution maps with the expected range of future temperature changes for the Hawaiian Islands by the mid and late 21st century. The expected surface warming and its uncertainty is analysed with an ensemble of global climate scenarios for two Representative Concentration Pathways (RCPs) scenarios (RCP4.5 and 8.5). It is found that the highest mountain elevations warm by a factor 1.5 ± 0.2 compared with the ambient surface temperature anomalies at the sea level. In scenario RCP8.5, high elevations above 3000 m reach up to 4–5 °C warmer temperatures by the late 21st century. The uncertainty due to multi‐model ensemble spread is overall larger than the statistical downscaling uncertainty, except for the highest elevations where both contribute equally to the uncertainty range. For the late 21st century, however, the largest uncertainty stems from the choice of emission scenarios.