A new study investigating summer marine heatwaves in the Northeast Pacific Ocean projects that they may become even more intense and longer-lasting than expected by long-term warming. This could have serious implications for marine ecosystems and fishery economics. The study was recently published in the journal Communications Earth & Environment by scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI).
What if the record-breaking 2019 Northeast Pacific marine heatwave occurred in a climate that was 4 °C warmer than today? The authors of the study answered this question by modeling the oceanic heatwave in different climates. They use a so-called storyline approach in which they simulate the event under different conditions: in preindustrial climate, in the present situation, and in a climate that is 4 °C warmer. This approach offers the opportunity to explore the effects of climate change in regards to thermodynamics and to understand the processes driving the evolution of extreme events. This is the first time it has been successfully applied to an oceanic extreme. “The storyline approach offers ‘what if’ scenarios that make the effects of climate change tangible for diverse audiences”, says Marylou Athanase, first author of the study and climate dynamics scientist at AWI, “We expect that this intuitive concept will be adopted by the research community and that our method and findings might well be utilized in numerous future studies on marine extremes.”
The study shows that marine heatwave events are likely to become more extreme in the future, even when accounting for the long-term rise of ocean temperatures due to climate change.
This is attributed to air-sea feedbacks that can modulate temperature changes within the marine heatwaves. The identified processes include reductions in clouds and ocean mixed-layer depth, and air advection, meaning air transport, from fast-warming subpolar regions. Looking at the complex interplay of these air-sea processes, they model their response to a 4 °C warmer climate. They find an overall amplification of the temperatures within the marine heatwave, particularly pronounced in the coastal and central Northeast Pacific.
Heatwaves in the ocean pose a threat to marine species and ecosystems, as temperatures can become too high for certain local organisms. Within such marine heatwaves, AWI scientists find that temperatures could increase by 50% more than the global long-term ocean warming. “The projected amplification we identified could thus place even greater stress than expected on marine ecosystems and fishery economics”, notes Marylou Athanase.
Original publication:
Athanase, M., Sánchez-Benítez, A., Goessling, H. F., Pithan, F., Jung, T. (2024) Projected amplification of summer marine heatwaves in a warming Northeast Pacific Ocean. Commun Earth Environ. https://doi.org/10.1038/s43247-024-01212-1