As greenhouse gas emissions continue to warm the world’s oceans, marine biodiversity could be on track to plummet within the next few centuries to levels not seen since the extinction of the dinosaurs, according to a recent study in the journal Science by Princeton University researchers.
The paper’s authors modeled future marine biodiversity under different projected climate scenarios. They found that if emissions are not curbed, species losses from warming and oxygen depletion alone could come to mirror the substantial impact humans already have on marine biodiversity by around 2100. Tropical waters would experience the greatest loss of biodiversity, while polar species are at the highest risk of extinction, the authors reported.
“Aggressive and rapid reductions in greenhouse gas emissions are critical for avoiding a major mass extinction of ocean species,” said senior author Curtis Deutsch, professor of geosciences and the High Meadows Environmental Institute at Princeton.
The study found, however, that reversing greenhouse gas emissions could reduce the risk of extinction by more than 70%. “The silver lining is that the future isn’t written in stone,” said first author Justin Penn, a postdoctoral research associate in the Department of Geosciences. “The extinction magnitude that we found depends strongly on how much carbon dioxide [CO2] we emit moving forward. There’s still enough time to change the trajectory of CO2 emissions and prevent the magnitude of warming that would cause this mass extinction.”
Deutsch and Penn, who initiated the study when both were at the University of Washington, combined existing physiological data on marine species with models of climate change to predict how changes in habitat conditions will affect the survival of sea animals around the globe over the next few centuries. The researchers compared their model to the magnitude of past mass extinctions captured in the fossil record, building on their earlier work that linked the geographic pattern of the End-Permian Extinction more than 250 million years ago — Earth’s deadliest extinction event — to underlying drivers, namely climate warming and oxygen loss from the oceans.
The researchers found that their model projecting future marine biodiversity, the fossil record of the End-Permian Extinction, and indeed the distribution of species that we see now follow a similar pattern — as ocean temperature increases and oxygen availability drops, there is a pronounced decrease in the abundance of marine life.
Water temperature and oxygen availability are two key factors that will change as the climate warms due to human activity. Warmer water is itself a risk factor for species that are adapted for cooler climates. Warm water also holds less oxygen than cooler water, which leads to more sluggish ocean circulation that reduces the oxygen supply at depth. Paradoxically, species’ metabolic rates increase with water temperature, so the demand for oxygen rises as the supply decreases. “Once oxygen supply falls short of what species need, we expect to see substantial species losses,” Penn said.
Marine animals have physiological mechanisms that allow them to cope with environmental changes, but only up to a point. The researchers found that polar species are more likely to go globally extinct if climate warming occurs because they will have no suitable habitats to move to. Tropical marine species will likely fare better because they have traits that allow them to cope with the warm, low-oxygen waters of the tropics. As waters north and south of the tropics warm, these species may be able to migrate to newly suitable habitats. The equatorial ocean, however, is already so warm and low in oxygen that further increases in temperature — and an accompanying decrease in oxygen — might make it locally uninhabitable for many species.
The researchers report that the pattern of extinction their model projected — with a greater global extinction of species at the poles compared to the tropics — mirrors the pattern of past mass extinctions. A study Deutsch and Penn published in Science in 2018 showed that temperature-dependent increases in metabolic oxygen demand — paired with decreases in oxygen availability caused by volcanic eruptions — can explain the geographic patterns of species loss during the End-Permian Extinction ago, which killed off 81% of marine species.
The new paper used a similar model to show that anthropogenic warming could drive extinctions from the same physiological mechanism at a comparable scale if warming becomes great enough, Penn said. “The latitude pattern in the fossil record reveals the fingerprints of the predicted extinction driven by changes in temperature and oxygen,” he said.
The model also helps resolve an ongoing puzzle in the geographic pattern of marine biodiversity. Marine biodiversity increases steadily from the poles towards the tropics, but drops off at the equator. This equatorial dip has long been a mystery — researchers have been unsure about what causes it and some have even wondered whether it is real. Deutsch and Penn’s model provides a plausible explanation for the drop in equatorial marine biodiversity — the oxygen supply is too low in these warm waters for some species to tolerate.
The big concern is that climate change will make large swathes of the ocean similarly uninhabitable, Penn said. To quantify the relative importance of climate in driving extinctions, he and Deutsch compared future extinction risks from climate warming to data from the International Union for Conservation of Nature (IUCN) on current threats to various marine animals. They found that climate change currently affects 45% of the marine species at risk of extinction, but is only the fifth-most important stressor after overfishing, transportation, urban development and pollution.
However, Penn said, climate change could soon eclipse all of these stressors in importance: “Extreme warming would lead to climate-driven extinctions that, near the end of the century, will rival all current human stressors combined.”
The paper, “Avoiding ocean mass extinction from climate warming,” was published April 29 in Science. The work was supported by grants from the National Science Foundation (OCE-1737282), the National Oceanic and Atmospheric Administration (NA18NOS4780167), California SeaGrant and Ocean Protection Council, and the UW Program on Climate Change.
METHOD OF RESEARCH
SUBJECT OF RESEARCH
Avoiding ocean mass extinction from climate warming
ARTICLE PUBLICATION DATE
And this is Rud’s take.
Ridiculous New Alarm—Climate Caused Mass Ocean Extinction!!
I was reading the electronic news today and spotted a Google News synopsis of a WaPo piece wailing about a new paper today (April 28, 2022) in Science, “Avoiding Ocean Mass Extinction from Climate Warming” by two Princeton ‘researchers’. This post is in three parts: what the WaPo reported, what the paper abstract said (the rest is paywalled), and what the SI shows is going on.
“One third of all marine animals will be extinct in 300 years, new research shows.” (The horror…)
“The new biological and climate models were tested by simulating the Permian extinction.” (So they must be right.)
“The climate models predict species behavior (like extinction) based on simulated organism types.” (Climate models of simulated organisms, sure.)
“Global warming threatens marine biota with losses of unknown severity. Here we quantify global and local extinction risks in the ocean across a range of climate futures on the basis of the ecophysiological limits of diverse animal species and calibration against the fossil record. With accelerating greenhouse gas emissions, species losses from warming and oxygen depletion alone (poster comment—the thesis is warmer water holds less dissolved oxygen (true) so hypoxia is an extinction mode) become comparable to current direct human impacts (IUCN red list, 89% of marine species NOT threatened at all) within a century AND culminate in a mass extinction rivaling those in Earth’s past.”
Associated Science editor comment: “A stark future for ocean life.”
OK, so the WaPo was actually reasonably reporting on Science hyperventilation. They may even have got the ‘1/3 in 300 years’ from the body of the paper I chose not to read after reviewing the SI. Just shows the alarmist echo chamber.
This is always a good skeptic cheapskate trick, since it is never paywalled and often reveals ‘dirty secrets’ not in the paper itself. As here, excerpted after downloading it.
The climate models used were 16 from CMIP5 and CMIP6. The global warming scenario in both was of course the physically impossible RCP8.5.
The ‘ecophysiotypes’ were based on warm water and hypoxia tolerance across several different orders of marine organisms including bony fishes, cephalopods, bivalves… They were estimated in figure S3, with the following R^2: 0.08, 0.08, 0.21, 0.03, 0.08, 0.05. In other words, just statistical junk ‘ecophysiotypes’.
The SI has the RCP8.5 models warming the ocean upper 500 meters by 2300 a stunning 5C on average (!!, SI figure S8), resulting in an O2 loss of about 30%. The problem is, 30% oxygen depletion isn’t close to marine hypoxia.
The best of all (sarcasm) was how they validated all this by showing they could simulate the Permian extinction (when almost 90 percent of marine organisms went extinct). I have done considerable research on the Permian extinction. It was almost certainly caused by the vast Siberian Traps flood basalt eruptions lasting almost 1 million years. This released vast amounts of SO2, which cooled the atmosphere but grossly acidified the oceans on washout. The eruptions were also through vast Siberian coal deposits, causing them to burn and release enormous quantities of CO2 to warm the atmosphere. We know this from coal ash deposits from the period in Chinese lakebeds. Now, the SO2 and CO2 would have offset some in the atmosphere, but NOT in the oceans. Which is why the Permian extinction was most severe on marine life, not terrestrial plant and animal life.
So these Princeton folks claimed to be able to simulate that and match the Permian fossil record using their CMIP5 and CMIP6 climate models, using their statistically dodgy ‘ ecophysiotypes’. But their SI graphical evidence in support of this claim simply does not do so. Nor could it ever have. As SI figure 1a and 1B amply demonstrate.