Rapid, high ocean temperature spikes occurring at double the expected rate affecting marine ecosystems and humans
Oceans globally are experiencing unusual and ‘surprisingly high’ temperatures more frequently than researchers previously expected. These warming events, including marine heatwaves, are occurring at nearly double the rate than the scientists expected. This is disrupting large marine ecosystems and the people who depend on them, say researchers, who identified "surprises" all over the world, including in the Arctic, North Atlantic, eastern Pacific, and off Australia.
The research team led by Dr. Andrew Pershing, Chief Scientific Officer at the Gulf of Maine Research Institute, defined the surprising ocean temperature, as an annual mean temperature that is “two standard deviations above the mean” of the previous three decades. They are called "surprises" as these are conditions that are unexpected based on recent history.
For the study, the team examined 65 large marine ecosystems from 1854-2018. The world’s oceans are divided into large marine ecosystems. According to the International Union for Conservation of Nature (IUCN), such ecosystems “covering large swaths of the world’s coast” have some of its richest marine biodiversity and provide goods and services to billions of people worth over $12 trillion each year.
The researchers found that the number of "surprising" warming events across the large marine ecosystems increased with global warming, especially after 1998. While the researchers expected that about six or seven of 65 ecosystems examined would experience these “surprises" each year,” they instead found an average of 12 ecosystems experiencing these warming events each year, over the past seven years. This includes a high of 23 "surprises" in 2016, says the team. In his previous research, Dr. Pershing had identified the Gulf of Maine as one of the most rapidly warming ecosystems in the global ocean.
“Based on historical and lived experience, people expect certain conditions to prevail in the ecosystems they depend upon. Anthropogenic (human impact on the environment) climate change is now introducing strong trends that push conditions beyond historical levels. Using ocean ecosystems as a case study, we show that the frequency of surprising temperatures is increasing faster than expected. According to our analysis, marine ecosystems are experiencing more frequent surprises, even accounting for recent warming trends,” says the study published in the Proceedings of the National Academy of Sciences (PNAS).
The team predicts that surprising temperatures are likely to reduce the diversity and productivity of marine ecosystems. The researchers looked at the associated impacts of these warming events on both natural and human communities. The research says that in natural communities - for example, coral reefs, fish, plankton - new species that prefer warmer conditions can often replace cold-loving species that suffer when an ecosystem warms. In gradually warming ecosystems, the changeover of species should be able to keep pace, according to the study. However, they warn, in ecosystems that are experiencing change much faster, these natural communities are expected to suffer reductions in both biomass and diversity.
“Our model of natural communities suggests that this will result in a decline in the abundance of species occupying a similar trophic niche; however, the decline will be less strongly felt by fast-reproducing species. This creates the potential for decoupling between different components of the food web. For example, some gelatinous zooplankton can double their abundance in a few days. While the species composition in a region will change, the fast-reproducing component of the ecosystem is more likely to maintain high biomass levels than slower-reproducing species such as fish,” the findings state.
According to the researchers, humans are also significantly impacted by an increase in the number of unusually high ocean temperatures. The researchers explored the challenge rapid ecosystem changes pose to people making decisions about ocean resources. “As the planet continues to warm, ecosystems and human communities are expected to adapt to the changing conditions. However, it is unclear whether such adjustments will keep pace as trends associated with climate changes accelerate,” the findings state.
The authors compared two strategies for making decisions about the ocean - one based on historical data and other based on possible future trends. The researchers say that the lesson is clear: historical experience is becoming less relevant, and history could become an unreliable guide for climate-change-related decision-making. They say to thrive in the future, marine communities need to make decisions based on climate trends rather than historical data.
The researchers explain that the results suggest that many large marine ecosystems are experiencing a high rate of warming, and extreme ocean temperatures will continue to rise. As these conditions are likely to push such ecosystems to their adaptation limits, they require forward-looking strategies for adaptation, according to the authors.
“As the number of these extreme warming events continues to rise, the results of this study highlight the importance of using climate projections and other predictive tools to make decisions about the future. To be successful, human institutions, including businesses, communities, management agencies, and governments will need to adopt strategies that look forward rather than backward,” the study recommends.