Frequency of marine heatwaves in the North
Atlantic and North Pacific since 1950
Hillary A. Scannell1,2, Andrew J. Pershing2, Michael A. Alexander3, Andrew C. Thomas1,
and Katherine E. Mills2
1School of Marine Sciences, University of Maine, Orono, Maine, USA, 2Gulf of Maine Research Institute, Portland, Maine, USA,
3NOAA/Earth System Research Laboratory, Boulder, Colorado, USA
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]...
