The heat is on
Anthropogenic climate change is causing not only more episodes of historically high air temperatures but also more frequent spells of unusually increased ocean temperatures. Marine heatwaves, defined as periods of anonymously high regional surface ocean temperatures, have also become common in recent decades. Laufkötter et al. show that the frequency of these events has already increased more than 10-fold because of anthropogenic global warming, making marine heatwaves, which typically occurred once in hundreds to thousands of years in preindustrial times, likely to occur on an annual to decadal basis if the global average air temperature rises by 3°C.
Science, this issue p. 1621
Marine heatwaves (MHWs)—periods of extremely high ocean temperatures in specific regions—have occurred in all of Earth’s ocean basins over the past two decades, with severe negative impacts on marine organisms and ecosystems. However, for most individual MHWs, it is unclear to what extent they have been altered by human-induced climate change. We show that the occurrence probabilities of the duration, intensity, and cumulative intensity of most documented, large, and impactful MHWs have increased more than 20-fold as a result of anthropogenic climate change. MHWs that occurred only once every hundreds to thousands of years in the preindustrial climate are projected to become decadal to centennial events under 1.5°C warming conditions and annual to decadal events under 3°C warming conditions. Thus, ambitious climate targets are indispensable to reduce the risks of substantial MHW impacts.
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