Back on June 26, 2025 – Science News Desk, A new scientific report is sending a strong message: what happened hundreds of millions of years ago could be happening again but much faster this time.
Echoes from Deep Time: Ancient CO₂ Spikes Warn of Fast-Moving Climate Crisis
On June 26, 2025, the Science News Desk reported a groundbreaking study that shines a stark light on Earth’s climatic past—and its unnervingly fast-moving present and future. Published just days earlier on June 23, 2025, in the prestigious journal Proceedings of the National Academy of Sciences, this research reveals that hundreds of millions of years ago, Earth's atmosphere experienced multiple, massive episodes of carbon dioxide (CO₂) spikes—dramatic increases that altered global climates and ocean ecologies over thousands of years. Remarkably, this historical phenomenon could be repeating today but at an alarmingly faster pace, driven principally by human activity.
Five Major CO₂ Spikes in the Deep Past
The study, led by Professor Isabel Montañez from the University of California, Davis, focuses on a critical window from roughly 310 to 290 million years ago. During this period—part of the late Carboniferous to early Permian eras—there were at least five significant CO₂ surges. These episodes released colossal volumes of CO₂ into Earth’s atmosphere due to extensive volcanic activity and underground coal seam fires.
To uncover this history, Montañez and her colleagues examined ancient rock samples from South China. These rocks were originally ocean sediments, allowing the scientists to piece together a comprehensive record of past atmospheric CO₂ levels and ocean oxygenation over those millions of years. Their analysis showed correlation between spikes in atmospheric CO₂ and subsequent dramatic drops in oxygen levels in the oceans.
The 304 Million-Year-Old Event of Ocean “Dead Zones”
One particularly severe event occurred about 304 million years ago. At that time, massive volcanic eruptions and coal fires emitted huge amounts of CO₂, causing global temperatures to rise substantially. Warmer oceans hold less dissolved oxygen, a problem compounded by meltwater from glaciers disrupting ocean circulation and oxygen distribution to deeper waters. The result was devastating: nearly 25% of the ocean floor became anoxic, or oxygen-free, establishing extensive “dead zones” where marine life struggled or perished.
These dead zones are not just relics of the past. Today, scientists worry about their expansion because oxygen-starved areas severely limit habitats for fish, corals, and countless other sea creatures essential to the health of marine ecosystems and human economies relying on fishing and tourism.
Insights from an Oxygen-Rich Ancient Atmosphere
A key point of concern from the research is the oxygen content in Earth’s atmosphere during that era. In the late Paleozoic, atmospheric oxygen was estimated to be up to 50% higher than today’s levels. Despite this oxygen-rich environment, the spikes in CO₂ still caused vast ocean oxygen losses. This fact is sobering for current conditions where oxygen levels are lower and CO₂ emissions are accelerating far faster than those ancient events.
Since the 1950s, oceanographers have observed a roughly 2% decline in oceanic oxygen levels worldwide due to rising temperatures and pollution. Projections from current trends suggest that we could lose an additional 3–4% of ocean oxygen by 2100 if greenhouse gas emissions continue unabated. This accelerated change could exacerbate marine dead zones and threaten biodiversity more severely than historic precedents.
Evolutionary Slowdowns and Ecosystem Stress
The researchers also noted that these ancient oxygen drops slowed evolutionary rates in marine life. Species diversity stalled as animals faced chronic oxygen starvation, halting biological innovation and adaptation for extended periods. While these CO₂-driven oxygen dips did not precipitate Earth’s largest mass extinctions, they nonetheless imposed intense ecological stress and reshaped marine habitats.
This evolutionary slowdown echoes the modern concern that rapidly changing ocean chemistry—due to warming, acidification, and oxygen depletion—may reduce the resilience of marine species to adapt, threatening ocean food webs and human livelihoods dependent on marine resources.
Modern Parallels and a Dire Warning
Professor Montañez emphasizes the importance of these ancient natural experiments: they offer the clearest analogs we have for understanding today’s climate crisis. The historic spikes demonstrate that large, rapid increases in atmospheric CO₂ can disrupt ocean oxygen levels and marine ecosystems even when the planet’s atmosphere had more oxygen than now.
Today’s carbon emissions are orders of magnitude faster, primarily fueled by fossil fuel combustion, deforestation, and industrial activity. This velocity of change leaves less time for ecosystems to adapt or recover, raising fears that we could soon witness a modern version of an ancient oceanic crisis if global emissions are not dramatically curtailed.
What Can Be Done to Protect Ocean Health?
Given these findings, scientists urge urgent action on multiple fronts. Reducing global CO₂ emissions is critical—not only to stabilize atmospheric greenhouse gases but also to protect ocean oxygen levels and biodiversity. Transitioning to renewable energy sources, implementing carbon capture technologies, and enforcing international climate agreements are key components.
Moreover, protecting marine environments through the creation and expansion of marine protected areas can safeguard vulnerable ecosystems. Monitoring ocean oxygen levels and “dead zones” with advanced technologies helps identify at-risk regions, enabling timely interventions.
Public awareness and education also play an essential role. Understanding the scientific link between atmospheric CO₂, ocean oxygen, and marine health empowers individuals, policymakers, and businesses to support climate-positive choices.
Conclusion: Lessons from the Past to Shape Our Future
This new research compellingly underscores that the Earth’s climatic and biological systems are deeply interconnected and vulnerable to abrupt environmental changes. The fossil record serves as a cautionary tale: even when oxygen levels were once high, huge surges of CO₂ triggered prolonged ecological crises in the oceans.
The rapid pace of today’s CO₂ emissions threatens a similar fate but accelerated, placing marine ecosystems—and by extension, all life dependent on healthy oceans—in jeopardy. Acting now to reduce emissions and protect ocean ecosystems offers the best hope of avoiding a catastrophic replay of Earth’s ancient carbon crises.
