The extreme marine heatwave known as The Blob lasted more than 350 days and expanded across much of the North Pacific Ocean. It was the biggest, longest marine heatwave in decades. Photo by NASA Physical Oceanography Distributed Active Archive Center
Sept. 24 (UPI) -- In 2015, a marine heatwave dubbed "The Blob" expanded across the Northern Pacific. At its peak, the mass of warm water extended more than 2,000 miles in length, measured 1,000 miles wide and extended several hundred feet beneath the ocean surface.
According to a new study, anthropogenic climate change has made extreme heatwaves like the Blob more likely. In fact, the study's authors claim human-caused global warming is directly to blame for the Blob.
"The Blob would not have occurred in a world without climate change," lead study author Charlotte Laufkötter, a marine scientist at the University of Bern in Switzerland, told UPI in an email.
The Blob was the largest and longest heatwave in the last half-century, covering a few million square miles of ocean and lasting more than 350 days.
"Twenty years ago, the longest heatwaves lasted approximately 50 days," Laufkötter said.
For the study, published Thursday in the journal Science, Laufkötter and her colleagues began by surveying satellite data to analyze the relationship between air and ocean temperatures and the development and evolution of several large modern marine heatwaves.
Next, researchers used climate models to gauge the influence of anthropogenic climate change on extreme marine heatwaves, or EMHs. Essentially, researchers simulated marine heatwaves in two world: a 'real' one, with modern levels of greenhouse gas emissions, and an imaginary one, or preindustrial one, without greenhouse gas emissions.
"Both worlds included the variability of the climate system. We then calculated the probability in both worlds with which a heatwave as large as the Blob occurs," Laufkötter said. "The difference between the two probabilities tells us to what extent heatwaves like the Blob are influenced by anthropogenic climate change."
"In case of the Blob this was 100 percent, or in other words the Blob would not have occurred in a world without climate change," she said.
Currently, there is a 1-in-100 chance that a marine heatwave as extreme as the Blob develops during any given year. In other words, the Blob was the equivalent of a 100-year flood. Those odds will shift as the climate continues to warm.
"Already, at 1.5 degrees [Celsius] of global warming, it will be a one in approximately 10 year event," Laufkötter said.
The hotter the planet and its oceans get, the more likely extreme marine heatwaves will become. At 3 degrees warming, simulations showed Blob-like heatwaves will become an annual occurrence.
The only way to ensure extreme marine heatwaves remain an anomaly, instead of commonplace, is to stop global warming.
"In my understanding, limiting global warming to 1.5 degrees is still possible if there is immediate and determined action from all nations to fight climate change," Laufkötter said. "However, the time window to do so is short. Global warming will likely rise to 1.5 degrees Celsius above pre-industrial levels between 2030 and 2052 if warming continues to increase at the current rate."
Marine heatwaves are a serious threat to environmental and human health. Over the last few decades, an uptick in marine heatwaves has triggered a rise in coral bleaching events, damaging the foundation of some of the ocean's most biodiverse ecosystems. Marine heatwaves can also increase the mortality of fish, as well as kill off seagrass and kelp forests.
"The Blob caused increased mortality of sea birds, salmon, and marine mammals, very low ocean primary productivity, harmful algal blooms and large alterations to open-ocean and coastal ecosystems," Laufkötter said.
Marine heatwaves also pose a threat to human populations on land, as they trigger extreme weather patterns, including drought, heavy precipitation and heat wave events.
Currently, most of what scientists know about marine heatwaves is from a surface-level perspective. Laufkötter hopes followup studies will offer deeper -- literally -- insights.
"Little is known about marine heatwaves at depth," she said. "We are also interested in marine extreme events other than heat, such as low chlorophyll, low oxygen or low pH events."