Marine heatwaves - prolonged periods of anomalously high ocean surface temperatures - are likely to become more frequent, extensive and intense as a result of global warming, according to a study published in this week’s Nature. The authors report that the number of marine-heatwave days doubled between 1982 and 2016, and this is projected to increase further if global temperatures continue to increase.
Thomas Frolicher and colleagues analysed past changes and assessed future trends in different marine-heatwave characteristics. Using daily global sea surface temperature data covering the period 1982-2016 and 12 global Earth system models for the period 1861-2100, the authors found that marine heatwaves will become more frequent, extensive, intense and longer-lasting as a result of continued global warming.
If temperatures were to rise by 3.5 degrees Celsius relative to preindustrial levels by the end of the 21st century, as is predicted to result from current national policies for the reduction of global carbon emissions, the authors found that the average probability of marine heatwaves occurring would be 41 times higher than in preindustrial times. On average, the spatial extent of the heatwaves would be 21 times larger, their duration would increase to 112 days and their maximum intensity would rise to 2.5 degrees Celsius. However, the authors note that these increases would be reduced if warming was limited to 1.5 or 2.0 degrees Celsius above preindustrial levels by the end of the century. Under a scenario in which temperatures rose by 1.5 degrees, the probability of marine heatwaves occurring would be 40% of that at 3.5 degrees.