You may have heard about or experienced a land heatwave characterized by prolonged periods of unusually high temperatures. However, in recent years, marine scientists have observed the same phenomenon in the world’s oceans. Currently, there is a significant cause for concern over heat waves that occur in the ocean, partially because of the impact they have on marine life, but mostly because these events are increasing in frequency and severity. In this article, we will look at the potentially destructive nature of marine heatwaves, what causes them, and how we can stop them before their effects on the marine ecosystem are permanent. But first, let’s talk about what a marine heatwave is and how it comes about.
About Marine Heatwave?
A marine heatwave occurs when the ocean’s surface becomes unusually hot for a prolonged period of time. As you might have guessed, this heatwave causes a rise in sea temperatures, which changes the marine ecosystem in a potentially permanent way.
Marine heatwaves can be traced as far back as the late fifties, although scientists have only recently begun to document them. To illustrate this point, the furthest instance of a marine heatwave was in 1958 in the Pacific, but NOAA satellites started tracking heat waves at sea in 1981—over 20 years later.
Between 2014 and 2016, the waters off the West Coast of the United States experienced what is now known as the largest marine heatwave ever recorded since 1981. It had a staggering impact on the marine environment and economy of the region. This particular heatwave came to be known simply as “The Blob.”
Even though marine scientists started to call these events marine heatwaves in 2015, it has been known for a while now that ocean temperatures and properties tend to fluctuate.
For instance, there was a similar “Blob” back in the winter of 2013 to 2014 due to a reduction in the ocean’s normal cooling period. The reason behind this heatwave was determined to be a blanket of exceedingly high atmospheric pressure that hovered over the northeast Pacific Ocean, blocking the path of storms that usually pass across the Gulf of Alaska and the West Coast. With no cool winds to mix up cold and warm water and dissipate the heat on the ocean’s surface as was the norm every winter, ocean temperatures rose steadily.
What Causes Marine Heatwaves?
The thing is, heat waves on land are similar to heatwaves in the ocean. They vary from place to place, just like a heatwave in Texas would have different characteristics from one in Seattle. Therefore, the natural variability of the ocean differs from one place to another. All this means is that some places have drastically fluctuating temperatures while others don’t. So, even mild temperature fluctuations are enough to create an anomaly that would affect the marine ecosystem for these places with low variability.
Still, marine scientists insist that something more than the ocean’s natural variability is behind the recent surge of intense marine heatwaves off the West Coast. They unanimously point the finger at the rising greenhouse gas concentrations that pump the atmosphere full of heat, ending up in the ocean. Therefore, when unusual weather patterns bore of the ocean’s natural variability cause temperature fluctuations at sea, they cause a further temperature rise on oceans that are already warmer than usual due to global warming.
According to the evidence they’ve collected, marine scientists speculate that climate change—particularly the continuous warming of the climate—will increase marine heatwaves’ frequency in the future. Already, heatwaves in the oceans are 20 times more frequent than they were a few decades ago due to human influence.
Are Marine Heatwaves Caused By Human Activity? What Does The Study Suggest?
To understand how human influence is linked to the increasing marine heatwaves scientists are recording, we first have to discuss anthropogenic climate change. This refers to the emission of greenhouse gases like carbon dioxide into the atmosphere due to human activity.
A study published by Charlotte Laufkotter, Jakob Zscheischler, and Thomas Frolicher in the scientific journal Science prove that heatwaves have become longer and more intense in all of the world’s oceans. In fact, these events have increased significantly in just a span of 40 years due to global warming.
The study shows that between 1981 and 2017, there were 27 major heat waves, each lasting about 32 days on average and hit peak temperatures of 4.8 degrees Celsius above normal sea temperatures.
Alarmingly, data from the most recent decade to be analyzed shows that 172 major marine heatwaves occurred, each lasting an average of 48 days and reaching temperature peaks of 5.5 degrees Celsius above long-term average sea temperatures.
As much as the ocean’s natural variability causes temperature fluctuations too, these deviations are extremely slight in comparison. Therefore, temperature changes as drastic as the ones recorded in the last decade have created extraordinarily adverse living conditions over an area that’s roughly 1.5 million square kilometers, a worrying predicament for a significant portion of the world’s marine organisms.
Anthropogenic climate change hasn’t just amplified the temperature deviations in the world’s oceans, but it has also increased marine heatwaves’ frequency by over 20 times.
Before the industrial revolution, such heatwaves were observed once every hundred or thousand years. Now, even if we could reduce global warming to just 1.5 degrees above long-term average temperatures, marine heatwaves will occur once per decade or century. But if the temperature rises steadily to 3 degrees, marine scientists expect to observe extreme events at least once a year, or every decade at most.
Marine Heatwaves: Their Devastating Impact on Wildlife
Joaquim Garrabou is a marine biologist who regularly dives around the Medes Islands in the Spanish region of Catalonia. Since 1983, these waters have been a Marine Protected Area due to the diverse marine life thriving in them.
But when Joaquim decides to survey to observe the effects of marine heatwaves on a type of soft coral called gorgonians, he barely has to descend beyond fifteen meters below the surface before he spots a large colony of the coral that has been ravaged by the extreme temperatures.
As a marine biologist, Joaquim knows that even the best-conserved coral colonies have at least a 5% mortality rate—10% at most. Over recent years, however, over 80% of this colony has been affected.
The water he descends into while conducting his grim survey should ideally be between 19 and 22 degrees Celsius, but instead, his thermometer reads 23 degrees. The Medes Islands are often in the grip of land heatwaves. The most recent one, which was recorded on July 1st and lasted 30 days, shows that the temperature is 3 degrees Celsius above the climactic mean calculated between 1974 and 2019.
The gorgonian colonies he’s inspecting are dying out even at depths of 40 – 50 meters. These coral reefs, which have a temperature tolerance threshold of 24 – 25 degrees Celsius, have been subjected to temperatures above their limits for weeks on end.
As Joaquim explains, such exposure can cause pathogenic virulence and physiological stress to the gorgonians, which is the reason behind the mass mortalities he is observing.
And it’s not just in the Medes Islands. Coral reefs beyond the Mediterranean—from California to Australia—are experiencing the brunt of rising sea temperatures. And the most sobering fact of the matter is that these are long-lived species that can live for hundreds of years, so they will need at least a century to recover even if global temperatures begin to drop at a consistent rate.
Marine Heatwaves Threaten Global Biodiversity
The persistent warming of the atmosphere presents a new threat to the world’s oceans’ global biodiversity. Although many of the world’s oceans are affected, the Indian, Pacific, and Atlantic oceans are particularly vulnerable to the effects of extreme regional ocean warming because they contain high levels of marine life biodiversity.
The marine ecosystems of these oceans are susceptible to adverse effects from heat waves due to the prevalence of location-specific species, the co-existence of high levels of biodiversity, and human activity such as fishing. As a result, marine heatwaves on these sections of the global ocean may have a lethal impact on kelp forests, corals, and seagrasses, which are critical foundation species that marine life depends on to thrive.
As anthropogenic climate change continues to drive up global temperatures, marine heatwaves are set to become extremely disruptive phenomena that will soon impact the distribution and provision of ecological products and services in the coming years.
How Can We Minimize Harm from Marine Heat Waves?
Marine heatwaves similar to the infamous Blob are being witnessed on more of the world’s oceans. They are expected to continue in frequency and intensity as a result of climate change. But scientists are at a loss on stopping them because there is no reliable way to predict a heatwave on the ocean.
At the moment, the reigning strategy is a reactive one, not a proactive one. Marine wildlife experts and fishers are often caught flatfooted, which means that only after a marine heatwave strikes do they scramble into action.
Still, oceanographers are busy trying to observe the patterns that emerge before such an event strikes so that they can better forecast them and prevent (or at least minimize) their staggering ecological and economic damage.
According to Eric Oliver, an assistant professor of oceanography at Dalhousie University (Nova Scotia), heatwaves are part of the ocean systems’ natural cycle. Even before the emission of greenhouse gases became a problem, ocean temperatures frequently fluctuated every day of the year, sometimes even becoming extremely cold or extremely warm.
The problem is that anthropogenic climate change has bumped up to average sea temperatures, so what scientists would previously consider as hot temperatures are witnessed more often. That means that every once in a while, huge sections of the ocean experience extraordinarily high heat.
Most ocean organisms have evolved to withstand hotter or cooler temperatures. Still, with ocean temperatures reaching unprecedented highs and experiencing prolonged durations of heat waves, many of these are pushed to mass mortality.
In 2011, the Australian government had to step in and ban blue crab fishing for a year after a heatwave in the Shark Bay pushed killed huge colonies of the blue crab. That move may have saved the blue crab population from sure extinction. However, sea abalones in the same region didn’t fare nearly as well—and they still haven’t recovered to date.
A lack of accurate predictions makes it hard to be proactive about marine heatwaves, according to Thomas Wernberg, who is an associate professor of marine ecology based at the University of Western Australia. Consequently, he recruited a group of scientists to study marine heatwaves in 2014, which has since created protocols for tracking, measuring, defining, and naming marine heatwaves.
Predicting heatwaves will have numerous ecological and economic benefits because fishers, aquaculturists, and wildlife managers will have more time to act. For example, fish farmers could hold off fishing the vulnerable species, and lawmakers could create seasonal fishing rules or turn heavily affected regions into protected areas.
Proactivity could also come in the form of human involvement. Fish and wildlife managers could store the seeds and animals of the most vulnerable marine species so that they can be restored after a devastating heatwave.
Climate scientist Dillon Amaya, who works at the University of Colorado, is hopeful that we will be able to predict marine heatwaves with remarkable accuracy as time goes by. Using a 2019 Pacific heatwave dubbed “The Blob 2.0” as a basis, he discovered that it emerged due to a lethargic weather system over the pacific that led to weaker winds than were normally experienced in that region.
The lack of cool winds to dissipate heat on the ocean’s surface that year led to the accumulation of stagnant air over the Pacific. Using this information and recent technology, Amaya can simulate marine heatwaves, a monumental step towards learning when, why, and how these heatwaves occur.
He explained that now marine scientists have gained enough insight to see them as the unique yet deterministic events they are, which wasn’t possible ten years ago. Creating simulations is currently the best way to learn the mechanics of heatwaves, which is a step in the right direction for predicting future marine heatwaves.
The Bottom Line
Marine heatwaves are natural phenomena that have been occurring throughout the history of the earth. But the recent rise in global temperatures resulting from greenhouse gas emissions is pushing up average ocean temperatures, making heat waves deadlier than ever to the global marine ecosystem.
The chances are high that marine heatwaves won’t slow down or stop any time soon, but scientists are already working on ways to accurately predict them to be proactive about saving our marine species.
Nevertheless, it is a problem that will persist endlessly as the greenhouse effect continues to increase global temperatures, consequently making heat waves that were previously only moderately devastating into extinction-level events for many critical marine species.