2.11.2020: Online Ocean Circulation and Climate Dynamics Colloquium

online 2 pm
Webex meeting room: https://geomar.webex.com/geomar/j.php?MTID=mc3fd174db2454055ee2dbf9d174e5d7d

Meeting number (access code): 137 941 9247
Meeting password: 8Ztj584VbWx

Abstract:
Marine heatwaves are important events in oceanic systems that can have devastating consequences for ecosystems, causing ecological changes and socioeconomic losses. Prominent marine heatwaves have occurred recently and attracted scientific and public interest, but comprehensive assessments of how these events have been changing globally is missing. Using daily satellite observations, daily in situ measurements, and gridded monthly in situ-based sea surface temperatures we identify significant increases in marine heatwaves over the past century. We further estimate future changes in marine heatwaves to the end of the 21st century, as simulated by CMIP5 global climate model projections. We find that from 1925 to 2016, global averages of marine heatwave frequency and duration have increased by 34% and 17%, respectively, resulting in a 54% increase in annual marine heatwave days. Importantly, these trends can largely be explained by the increase in mean ocean temperatures, rather than a change in variability. Future projections show significant, and accelerating, increases in MHWs properties into the 21st century with many parts of the ocean reaching a near-permanent MHW state by the late 21st century, regardless of emissions scenario considered (RCP4.5, 8.5). Comparison with simulations of a natural world, without anthropogenic forcing, indicate that these trends have emerged from the range of natural variability within the first two decades of the 21st century. This implies that the climate system has departed significantly from natural marine heatwave conditions under which ecosystems evolved, and therefore impacts on marine ecosystems can be expected to be widespread, significant and persistent.

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