Severe marine heatwaves, like 2015's Pacific "blob," are far more likely to occur now than before human-induced global warming began, according to a new study. The findings underscore the importance of achieving ambitious climate goals to reduce the risks of marine heatwaves (MHWs) and avoid irreversible damage to marine ecosystems worldwide. In the last several decades, MHWs - localized periods of extremely high ocean temperatures - have been observed in all Earth's oceans. The longest and largest of which, often referred to as "the blob", occurred between 2013 and 2015 and saw sea temperatures in the north Pacific increase by more than 2.5 degrees Celsius (°C). Like many others in the recent past, this event has had severe impacts on marine organisms and ecosystems and the economic systems they support. However, very few studies to date have explored the link between global warming and the frequency and severity of MHWs. To better understand the human influence on these events and how they've changed due to our rapidly warming world, Charlotte Laufkötter and colleagues evaluated seven of the largest, most impactful and most recent MHWs. Using modeled simulations, they calculated how likely it would be for each to occur during preindustrial and modern climate conditions. The results show that the probabilities of high-impact MHWs occurring have significantly increased due to anthropogenic climate change. According to Laufkötter et al., the most impactful MHWs observed in the last decade would have occurred once every hundreds to thousands of years in preindustrial climate. These same events are projected to occur on a centennial to decadal basis under 1.5°C warming conditions and on a decadal to annual basis should the global average atmospheric temperature rise by 3 °C.
