ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Science 07 Dec 2018: Vol. 362, Issue 6419, eaat1327

These authors report the frequencies of Metabolic Index traits in living species and used these values to define a set of model ecophysiotypes. They then populated the model Permian ocean with each ecophysiotype, and found that ocean warming increases the metabolic O2 demand amid declining supply; this removes the aerobic habitats for the vast majority of ecophysiotypes and implies a high likelihood of extinction.

We are in the midst of an extinction crisis - the so-called 6^th extinction, but compared to the largest extinction in Earth’s history, which occurred at the end of the Permian Period, ours is slow. That “Great Dying,” (~252 million years ago) saw the loss of up to 96% of all marine species and 70% of terrestrial species. They conclude that rapid global warming and accompanying ocean oxygen loss were responsible for the majority of recorded extinctions. Tolerances of marine animals to warming and oxygen loss are physiologically related and are represented in the ratio of temperature-dependent oxygen supply and demand rates, termed the Metabolic Index (φ). If climate warming and oxygen loss reduce φ below the species-specific minimum requirement, the ocean would no longer support active aerobic metabolism and long-term population persistence.

Using a model of the Earth’s climate and coupled geochemical proxy data, the imposed increase in atmospheric greenhouse gas levels raises near-surface ocean temperatures. Extinction intensity should have been lower in the tropics than at high latitudes. Across diverse taxonomic groups, the observed extinction intensity increases with latitude, consistent with the predicted signature of aerobic habitat loss. Temperature-dependent hypoxia can account for more than half of the observed magnitude of regional extinction. These results highlight the future extinction risk arising from a depletion of the ocean’s aerobic capacity that is already under way.

An important factor not considered in this study is the rate of climate change during the end-Permian event. If warming and oxygen loss were imposed slowly, perhaps high-latitude organisms could adapt to warming and oxygen loss, whereas if these changes happened quickly, massive die-off would occur. Existing data suggest that the rates of these changes were rapid.