In late 2013, a huge patch of water along the North American coast heated above typical seasonal temperatures.
This enormous increase, dubbed the "Blob" after a 1958 horror film about an alien life form that grows as it consumes everything in its path, lasted for an abnormally long time, killing fish, birds, and other marine mammals, especially in 2015 and 2016.
According to a research published in the journal Nature Communications Earth and Environment, the Blob has appeared in at least two occasions since then, and now, a team of scientists has pinpointed the systematic warming in the Pacific Ocean that fueled the Blob's growth. The source of the Blob is not natural climatic variation, but human influences.
A group of researchers led by Armineh Barkhordarian, an expert on atmospheric science and member of the Universitat Hamburg's Cluster of Excellence "Climate, Climatic Change, and Society," demonstrated how the long-term warming pool has contributed to local marine heatwaves.
The most recent marine heatwave, which lasted from 2019 to 2021, caused water temperatures to rise by up to six degrees Celsius. According to the study, the extreme event was directly caused by increasing manmade greenhouse-gas emissions. The probability of such a heatwave occurring without all of the excess greenhouse gasses humans have pumped into the atmosphere is less than one percent.
The team also found that the water temperature above the warming pool in the northeast Pacific increased by 0.05 degrees Celsius (32.09 degrees Fahrenheit) per year over the previous 25 years. During the cold season, the team also observed a decrease in low clouds, which generally have a cooling effect on the water below. During the winter, this intensifies the atmospheric high-pressure systems above the warm water pool.
Overall, the area saw summers that were 37 days longer on average, and winters that cooled off less. As a result, there have been 31 marine heatwaves in this area alone during the past 20 years, compared to only nine from 1982 to 1999.
"This warming pool will continue to increase the water temperature in the future, increasing both the frequency and intensity of local marine heatwaves," Barkhordarian explained in a press release.
The findings are consistent with previous research that foundthat human-caused climate change is 20 times more likely now.
"More frequent and extreme marine heatwaves are a significant burden on affected ecosystems. This not only poses a significant threat to biodiversity, but it can also push these marine ecosystems past a tipping point, after which they cannot continue to recover," Barkhordarian said. "The discovery of the long-term warming pool will now provide us with essential information about the possibility of such extreme events in the future."
Huge pockets of unusually warm water are becoming more common around the world, including new warm areas in the North Pacific Ocean and elsewhere. However, heat waves will become more frequent, stronger, and lasting longer if global warming continues. Oceans are in danger of a mass extinction event comparable to the "Great Dying."
By the end of the century, our oceans might drastically alter, which underscores the urgency of reducing our reliance on fossil fuels.