Mean warming not variability drives marine heatwave trends
Marine heatwaves have been shown to be increasing in frequency, duration and intensity over the past several decades. Are these changes related to rising mean temperatures, changes to temperature variability, or a combination of the two? Here we investigate this question using satellite observations of sea surface temperature (SST) covering 36 years (1982–2017). A statistical climate model is used to simulate SST time series, including realistic variability based on an autoregressive model fit to observations, with specified trends in mean and variance. These simulated SST time series are then used to test whether observed trends in marine heatwave properties can be explained by changes in either mean or variability in SST, or both. We find changes in mean SST to be the dominant driver of the increasing frequency of marine heatwave days over approximately 2/3 of the ocean; while it is the dominant driver of changes in marine heatwave intensity (temperature anomaly) over approximately 1/3 of the ocean. We also find that changes in mean SST explain changes in both MHW properties over a significantly larger proportion of the world’s ocean than changes in SST variance. The implication is that given the high confidence of continued mean warming throughout the twenty-first century due to anthropogenic climate change we can expect the historical trends in marine heatwave properties to continue over the coming decades.
KeywordsExtreme event Climate change Stochastic model Sea surface temperature
This study makes a contribution to the International Marine Heatwaves Working Group (http://www.marineheatwaves.org). NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://www.esrl.noaa.gov/psd/. This work was supported by the National Sciences and Engineering Council of Canada (NSERC) Discovery Grant RGPIN-2018-05255.
- Hasselmann K (1976) Stochastic climate models part I. Theory Tellus 28(6):473–485Google Scholar
- Priestley MB (1981) Spectral analysis and time series. Academic Press, New YorkGoogle Scholar
- Smale D, Wernberg T, Oliver ECJ, Thomsen M, Harvey B, Straub S, Burrows M, Alexander L, Benthuysen J, Donat M, Feng M, Hobday A, Holbrook N, Perkins-Kirkpatrick S, Scannell H, Sen Gupta A, Payne B, Moore P (2019) Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nat Clim Change. https://doi.org/10.1038/s41558-019-0412-1 Google Scholar
- Stocker T, Dahe Q, Plattner GKE (2013) Working group I contribution to the IPCC fifth assessment report climate change 2013, the physical science basis. IPCCGoogle Scholar