Pacific Ocean ‘marine heatwaves’ likely to become more frequent, intense

By Kipp Robertson
3 April 2016 (MyNorthwest.com) – That oceanic “blob” that has been at least partially to blame for Washington’s warmer weather is real, and recent research shows it could return more frequently. A paper co-authored by Hillary Scannell, a University of Washington oceanographer and doctoral student, notes that the “blobs” are not as rare as some may have originally thought. Furthermore, we should expect more in the future. Marine “heat waves” are “likely to become more frequent and intense,” the paper states. That goes right along with what others have said in the past, such as state climatologist and University of Washington Professor Nick Bond. He told KIRO Radio’s Ron and Don that while the “blob” in the Pacific Ocean is a “short-term climate event,” it is something that we will see more in the future. “The globe has warmed,” he said. “Temperatures here in Washington state, especially nighttime temperatures in the summer, have warmed over the last century.” The “blob” off Washington’s coast is thought to be a contributing factor to our warmer weather and the low snowpack between 2014 and 2015. The water warms the air above it, which then increases temperatures on land. [more]

Pacific Ocean’s ‘marine heatwaves’ likely to become more frequent, intense

ABSTRACT: Extreme and large-scale warming events in the ocean have been dubbed marine heatwaves, and these have been documented in both the Northern and Southern Hemispheres. This paper examines the intensity, duration, and frequency of positive sea surface temperature anomalies in the North Atlantic and North Pacific Oceans over the period 1950–2014 using an objective definition for marine heatwaves based on their probability of occurrence. Small-area anomalies occur more frequently than large-area anomalies, and this relationship can be characterized by a power law distribution. The relative frequency of large- versus small-area anomalies, represented by the power law slope parameter, is modulated by basin-scale modes of natural climate variability and anthropogenic warming. Findings suggest that the probability of marine heatwaves is a trade-off between size, intensity, and duration and that region specific variability modulates the frequency of these events.

1 Introduction

Heatwaves on land are becoming more frequent, intense, and persistent due to anthropogenic climate change, and these events have had major impacts on human health and economic productivity [Meehl and Tebaldi, 2004; Stott et al., 2004; Trenberth et al., 2007]. A similar phenomenon in the ocean has recently been identified and is associated with adverse consequences to both fishery productivity and marine ecosystems [Pearce et al., 2011; Mills et al., 2013]. These events have been referred to as marine heatwaves and have been described as regions of large-scale and persistent positive sea surface temperature (SST) anomalies [Pearce et al., 2011]. Well-known marine heatwaves have occurred in the Mediterranean Sea [Black et al., 2004; Olita et al., 2007], off Western Australia [Pearce and Feng, 2013], in the northwest Atlantic [Mills et al., 2013; Chen et al., 2014, 2015], and in the northeast Pacific [Bond et al., 2015; Hartmann, 2015]. Like heatwaves on land, marine heatwaves are likely to become more frequent and intense under continued anthropogenic warming assuming fixed temperature thresholds [Solomon et al., 2007]. However, if temperature fluctuations are examined about the mean warming trend, marine heatwaves occur as spatially and temporally isolated extreme events. This reasoning suggests a level of stochasticity in the likelihood of heatwaves akin to analogous atmospheric phenomena [e.g., Hunt, 2007; Teng et al., 2013].