Marine species could make drastic shifts in their historic ranges as the earth warms, changes in the ocean that haven’t been seen in 3 million years, according to a new study.
That reorganization of marine biodiversity won’t be as drastic if the world limits warming to 2°C, according to the study, which was published this week in Nature Climate Change. But scenarios with higher than 2°C warming, especially those that see the earth warming an average of 2.2°C to 3.7°C by 2100, pose a large threat to marine species, causing many of them to migrate from their historic ranges in search of cooler waters.
In a warmer world, species could move out of the tropics — a region that, right now, is rich in marine biodiversity — and into the polar regions. That migration poses dangers for species already living in the poles, who could be out-competed for food and space by these newcomers. This change in ocean biodiversity could be more drastic than any seen in the last 3 million years, the study found. That’s worrisome for ocean ecosystems, and also for the fishermen who depend on certain species of fish to be present in certain locations.
To come to their findings, the researchers set up a model using tens of thousands of “pseudo-species.” The model world was made up of different theoretical species occupying different ecological niches, an environment that the researchers made accurate by checking it against data on existing species. Gregory Beaugrand, lead author of the study and director of research at the National Center for Science Research in France, said that the scientists developed this pseudo-species model because science has identified so few of the ocean’s actual species — an estimated 200,000, or 10 percent, in all.
“For those species, we know very little about their biology and ecology (e.g. spatial distribution),” Beaugrand said in an email. “In such a case, the investigation of the implications of climate change for marine biodiversity is challenging, for the past, the present and the future. That is why we have created theoretical species, we created tens of thousands of them and allowed them to colonize the ocean provided they can withstand the local climatic regime.”
The researchers were then able to model how the pseudo-species would react under different warming scenarios, and were able to compare these predictions to marine biodiversity levels during the last ice age about 20,000 years ago and the mid-Pliocene period 3 million years ago. During the mid-Pliocene, carbon dioxide concentrations in the atmosphere were at about 400 ppm, and temperatures were about 2°C to 3°C higher than they are today.
The researchers found that, under the most drastic warming scenario — in which temperatures would likely rise an average of 3.7°C by 2100 — biodiversity in 70 percent of the oceans is expected to change more than it has at any point since the mid-Pliocene. That most dramatic warming scenario is largely considered the “do-nothing” scenario — what will happen if countries around the world don’t do anything to address climate change. Since countries are making strides to curb carbon emissions, it isn’t likely we’ll reach this scenario — but since climate models don’t typically take into account carbon feedback loops like permafrost melt, it isn’t out of the question.
Other emissions scenarios that call for less warming than the most drastic scenario but more than 2°C, however, also pointed to a change in biodiversity more drastic than any other since the mid-Pliocene in 46 to 51 percent of the world’s oceans.
“This is quite worrying to see that in a century we could have changes in biodiversity that we could compare to changes that happened between a glacial and an interglacial period,” Beaugrand said. Those changes, he said, likely took place over a time period of about 5,000 years. “The only possibility to avoid such changes is to control global warming and to remain below the threshold of 2°C.”
Though the researchers didn’t look into extinction possibilities in this study, Beaugrand said they were planning to in future studies.
Beaugrand’s study isn’t the first to warn of the drastic changes that could come to the ocean as the planet warms. One study from January concluded that if humans don’t curb carbon emissions soon, they risk causing a massive extinction in the oceans. Another study from 2014 found that certain species will move northward as waters warm. And though the study didn’t address ocean acidification — which is occurring as increased carbon emissions lower the pH of the oceans — it’s also making life difficult for some marine species, particularly shellfish, whose larvae have trouble forming shells if water is too acidic.