Marine heatwaves are becoming more frequent under global warming and this is having a significant impact on species' ability to recover.
Marine heatwaves are becoming more frequent under global warming and this is having a significant impact on species' ability to recover.
Since April, the world has seenÌýÌýand that's bad news for the plants and animals that call the ocean home.
Longer and more frequent bouts of extreme temperatures can cause the exodus of some species and the invasion of others, with potentially devastating impacts on the resident ecosystem.
Global warming manifests as a gradual increase in temperatures over time around the world, caused by increased greenhouse gas emissions.
However, scientists are finding that theÌýÌýcome from short-term spikes in temperature.
In the ocean, these discrete periods of extreme temperatures, lasting weeks to months, are calledÌý.
Marine heatwavesÌýÌýeither the atmosphere or by ocean processes.
For example, weather systems likeÌýÌýcan lead to low cloud and greater solar heating while ocean changes can be driven by strengthened poleward currents that move heat from high to low latitudes.
The likelihood and intensity of these atmospheric and oceanic drivers of marine heatwaves can also be affected by large-scale phenomena likeÌýÌýor La Niña.
Larger portions of the oceans are likely to experience marine heatwavesÌý.
Marine heatwaves can have dramatic impacts on marine organisms and ecosystems that may extend for long periodsÌý.
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Image: National Oceanic and Atmospheric Administration
Impacts range from theÌýÌýto mass deaths in fish and marine mammals, encroachment of invasive species andÌý.
Importantly, marine heatwaves have been associated withÌýÌýlike coral reefs, kelp forests and seagrass beds that form the homes and breeding grounds for a large amount of the ocean's biodiversity.
These impacts can have devastating knock-on effects for fisheries, aquaculture and tourism industries, with individual events linked toÌý.
Ìýwas an iconic extreme event.
Intensified winds along the Pacific equator — associated with an extreme La Niña —ÌýÌýand through the Indonesian Archipelago, into the Indian Ocean and poleward along the coast of Western Australia.
This flood of warm water caused a record-breaking marine heatwave thatÌýÌýfor over 100 km along the Australian coast along with one-third (1,300 square kilometres) of theÌý, a UNESCO world heritage site.
The Ningaloo Niño caused deaths and reduced reproduction in abalone, scallops and crabs that led to theÌý.
The Tasman Sea is another hotspot for ocean warming and marine heatwaves.
Two consecutive extreme events occurred the summer of 2015/16 and 2017/18. Their causes were very different.
The first was primarily caused byÌýÌýwhile the second was caused by aÌý.
These and previous events brought an invasion of sea urchins from mainland waters that led to the decimation of kelp forests off eastern Tasmania.
The 2015/16 event alone led to new diseases in cultured oysters, poor salmon performance and high mortalities of abalone. Together this led to.
As marine heatwaves exist on theÌý, these extreme events are becoming more intense and more frequent.
Over the past century the number of days each year experiencing marine heatwave conditions hasÌý.
The shorter time between marine heatwaves means that many populations no longer have the time to recover between events, which can lead to species moving their range or being wiped out.
And this will only worsen in the future.
Ìýshow that some coral reefs areÌý.
And with increased future warming theÌýÌýare in doubt.
Since April, the oceans have been warmerÌý.
It's probably at least 100,000 years — before the last ice age — since temperatures could have been this warm.
As a consequence, scientists are seeing more of the ocean experiencing marine heatwave conditions than ever. And that's before the added push from the developing El Niño.
Over the past few weeks alone, there have been extreme marine heatwaves in all of the ocean basins, including around the UK and Japan, off Peru and in waters extending off of the Californian, Florida and east and west Canadian coasts.
As the Northern Hemisphere enters its warmest season, marine heatwaves are at their most dangerous, pushing marine organisms above their thermal limits.
Over the next few months, expect reports of significant ecosystem harm to start to emerge.
An understanding of the physical drivers of these events and their biological impacts provides scientists with some ability to forecast their likelihood in the future.
This can help marine resource managers make decisions, like moving aquaculture stocks, reducing fishing quotas or taking direct action to suppress warming (like shading of aquaculture cultivation areas, or moving aquaculture pens out of harm's way) in small, high-value regions.
But ultimately, to avoid escalating impacts the only solution is to stop greenhouse gas emissions.
Associate Professor Alex Sen GuptaÌýis a research scientist and lecturer at the Climate Change Research Centre and the Centre For Marine Science and Innovation at UNSW. His work revolves around the role of the ocean in the climate system, how the ocean influences regional climate and what global climate models tell us about the future of the ocean, with a recent focus on marine heatwaves.
Associate Professor Sen Gupta's research has been funded by the Australian Research Council.
Dr Katie SmithÌýis a postdoctoral research assistant at the Marine Biological Association in the UK. Her research interests include understanding the impacts of climate change on marine species, throughout their life history and from individual to whole-ecosystem level.
Originally published underÌýÌýbyÌý.
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