VU Researchers Reveal Link Between Climate Regime Shifts and Mass Extinctions

Over the past 539 million years, Earth’s climate and carbon cycle have not changed gradually. Instead, they remained in relatively stable states for extended periods, separated by comparatively abrupt transitions. Vilnius University (VU) Faculty of Chemistry and Geosciences geologist and palaeontologist Professor Andrej Spiridonov and his doctoral researcher Robertas Stankevičius, together with an international team of scientists, have identified five such long-term Earth system regimes.

The study, published in Nature Communications, shows that life was most vulnerable during transitions from one long-term climate and carbon-cycle state to another. During these transitional periods, biological stress increased, rates of species turnover accelerated, and the risk of extinction rose.

What Determined the Scale of Mass Extinctions?

“Mass extinctions throughout Earth’s history are usually associated with specific catastrophes: massive volcanic eruptions, rapid global warming, oxygen depletion and acidification of the oceans, or asteroid impacts. However, our study suggests that these events should be viewed within a broader context,” says Prof. Spiridonov.

According to him, the long-term climate state, or megaclimate, determines how the Earth system and the biosphere respond to much more rapid disturbances, such as abrupt warming or an increase in atmospheric carbon dioxide concentrations. The sensitivity of the Earth system to such changes varied across different geological periods. The study showed that life was more vulnerable under persistently warm climatic conditions. Knowing the immediate trigger of a crisis is therefore not enough; it is also important to understand the state of the entire Earth system at the time.

The researchers emphasise that transitions between climate regimes were not the direct cause of every mass extinction. Rather, the long-term structure of the climate and carbon cycle created a general background of biosphere vulnerability, which influenced how strongly life responded to volcanism, rapid warming, changes in the oceans, or an asteroid impact.

Five Long-Term Regimes Identified in Earth’s History

The researchers analysed the past 539 million years, covering the entire Phanerozoic Eon, during which complex life evolved and diversified. They combined stable carbon and oxygen isotope data, reconstructions of ancient temperatures and atmospheric carbon dioxide levels, and the history of marine biodiversity.

“Using recurrence analysis, early-warning indicators of critical transitions, and a mathematical model of the climate and carbon cycle, we identified five long-term megaclimate regimes. The Earth system remained in these states for tens or even hundreds of millions of years before transitioning to another relatively stable state,” explains Prof. Spiridonov.

These regimes encompassed very different stages of Earth’s history, ranging from the greenhouse climate of the early Palaeozoic and the late Palaeozoic ice age to the Mesozoic greenhouse and the subsequent cooling of the Cenozoic.

The researchers called these states “Haggis” intervals. The name was inspired by the traditional Scottish dish and by the recurrence plots, whose variegated, block-like structure represents the repetition of different system states.

Prof. Spiridonov was particularly surprised by how clearly the Cambrian and Ordovician periods differed from other stages of Earth’s history. Many of the principal animal body plans found today emerged during this period, when biosphere vulnerability was also at its highest.

“The recurrence plots showed that the carbon-cycle state of the Cambrian and Ordovician periods was genuinely exceptional. The remaining approximately 450 million years of the Phanerozoic, beginning with the Late Ordovician mass extinction, displayed much greater recurrence. This was probably related to the emergence and establishment of land plants on the continents, as they fundamentally altered the cycling of carbon within the Earth system,” he says.

Researchers Developed a Biosphere Vulnerability Index

To assess the condition of life during different periods, the researchers calculated a biosphere vulnerability index. It incorporates not only extinction rates but also the emergence of new taxa, overall organism turnover, and the level of biological diversity existing at the time.

“A high index value means that the biosphere is undergoing rapid restructuring: some groups of organisms disappear, while others emerge or replace them. Environmental stress is usually associated primarily with extinctions, but it can also be reflected in the rapid emergence of new species or genera. When environmental conditions change abruptly, a species may become extinct, but isolated populations may also adapt rapidly to new conditions and eventually develop into new species.

“The vulnerability index therefore captures overall taxonomic turnover and assesses it in the context of total biodiversity: the greater the diversity, the broader the ecological space in which life can exist. A rapidly restructuring biosphere experiences greater macroevolutionary stress and may respond more sensitively to additional environmental disturbances,” explains Prof. Spiridonov.

According to the researcher, peaks in vulnerability coincided with almost all the periods of elevated extinction examined in the study, including the so-called Big Five – the five largest mass-extinction crises in Phanerozoic history. Particularly pronounced increases in vulnerability were recorded during the early and middle Palaeozoic and at the Permian–Triassic boundary, when the largest known mass extinction occurred.

The study also revealed substantial differences between long-term climate states. During the warm early Cambrian, the biosphere remained consistently vulnerable, whereas its vulnerability was lowest during the generally cool Cenozoic. This suggests that long-term temperatures and the boundaries of the climate system helped shape the broader background against which extinction risk developed.

Distinguishing the Cause of a Crisis From the State of the Biosphere

Until now, mass-extinction crises have often been studied as individual events, with research focusing primarily on identifying their immediate triggers. The new framework makes it possible to distinguish between two separate factors: the specific event that triggered a crisis and the long-term environmental conditions that may have made the biosphere particularly sensitive at the time.

“Long-term climate regimes created a certain baseline level of biological stress. Shorter-term climatic fluctuations and catastrophic events occurred within an environment already shaped by those conditions. A severe biological crisis could therefore arise without a transition of the entire climate system, but its impact depended on the system’s preceding state,” says the VU researcher.

The authors note that their framework is designed for global and interregional datasets rather than individual geological sections. Ancient geological records vary in resolution and contain gaps and chronological uncertainties. The boundaries of the identified regimes and their relationship with different biological crises will therefore need to be tested through further research.

In the future, the method could be applied to individual groups of organisms, ecosystems, regions, and different geological periods. This could help reveal which forms of life were most sensitive to climate-system transitions and whether the same environmental disturbance genuinely produced biological consequences of different magnitudes under different long-term Earth system states.

The research was conducted by scientists from Vilnius University, The Open University in the United Kingdom, the University of New Mexico, the Potsdam Institute for Climate Impact Research, the University of Potsdam, and the UK’s National Physical Laboratory.

Prof. Spiridonov contributed to formulating the general methodological approach used to link climate states with macroevolutionary indicators. He also proposed and formalised the concept of biosphere vulnerability and carried out the empirical calculations. Doctoral researcher Robertas Stankevičius conducted a central part of the study’s recurrence analysis and contributed to the development of new methods for calculating the recurrence of climate and evolutionary states.

The research originated in an international scientific working group in Edinburgh supported by the Isaac Newton Institute for Mathematical Sciences and the International Centre for Mathematical Sciences’ Mathematics for Humanity programme. The Lithuanian researchers were supported by the Research Council of Lithuania under project S-MIP-24-62, “BretEvoGeneralized”.