How Carbon Dioxide Threatens Both Corals and Human Health

As global temperatures rise, new research highlights a shared physiological vulnerability between humans and coral reefs driven by increasing carbon dioxide levels, according to a perspective published in The Lancet on April 18, 2026. The article underscores that while the ecological threats to coral reefs from ocean warming and acidification are well documented, emerging evidence suggests that elevated CO₂ may also disrupt fundamental biological processes in humans in ways that are not yet fully understood.

The perspective, authored by an interdisciplinary team of marine biologists, environmental health researchers and physiologists, argues that the dismissal of carbon dioxide as a direct health threat to humans—based on its role as a natural component of respiration—may be overly simplistic. While CO₂ is not toxic at atmospheric levels, the researchers note that sustained increases in ambient and dissolved CO₂, particularly in urban indoor environments and oceanic systems, may interfere with acid-base balance, oxygen transport, and cellular signaling pathways conserved across species.

In corals, rising seawater CO₂ leads to ocean acidification, which impairs calcification—the process by which corals build their calcium carbonate skeletons. This weakening of skeletal structure makes reefs more vulnerable to erosion and storm damage, compounding the stress from bleaching events caused by heat. The authors draw a parallel to human physiology, noting that disturbances in bicarbonate buffering and pH regulation—central to both coral calcification and human respiratory and renal function—could be disrupted under chronic CO₂ exposure.

“We initially thought of CO₂ as a passive byproduct of metabolism, not an active disruptor,” said Dr. Lena Torres, lead author of the perspective and a researcher at the Scripps Institution of Oceanography. “But the data show that both coral and human cells respond to shifts in CO₂ and pH with changes in gene expression, enzyme activity, and ion channel function. These are ancient, conserved mechanisms—what harms a coral’s ability to build its skeleton may, over time, affect how human cells manage energy, pH, and oxidative stress.”

The perspective cites recent studies showing that prolonged exposure to moderately elevated CO₂ levels—such as those found in poorly ventilated indoor spaces or projected future outdoor urban environments—can lead to subtle but measurable effects in humans, including reduced cognitive performance, altered sleep patterns, and changes in kidney bicarbonate handling. While these effects are not acute or immediately dangerous, the researchers warn that chronic, low-grade physiological strain could contribute to long-term health risks, particularly in vulnerable populations.

These findings align with broader concerns about the health impacts of climate change that extend beyond extreme weather and infectious disease. The World Health Organization has previously identified air quality, heat stress, and food and water insecurity as key climate-related health risks. This perspective adds a novel dimension by focusing on the direct biochemical consequences of rising CO₂, independent of temperature or pollution.

However, the authors emphasize that the evidence for direct CO₂ effects on human health remains observational and mechanistic, drawn largely from laboratory studies, environmental epidemiology, and comparative physiology. They caution against interpreting these findings as proof of imminent harm, stressing instead the need for longitudinal human studies and improved monitoring of indoor and outdoor CO₂ levels in relation to health outcomes.

“We are not suggesting that CO₂ is a toxin in the traditional sense,” Torres clarified. “But we are urging a reevaluation of the assumption that because CO₂ is natural and essential to life, it cannot become harmful under altered conditions. Just as too much oxygen or water can be disruptive, so too can an imbalance in CO₂—especially when it persists over years or decades.”

The perspective concludes by calling for greater collaboration between climate scientists, marine researchers, and public health experts to study shared biomarkers of stress in humans and corals. Such interdisciplinary work, the authors argue, could reveal early warning signals applicable to both ecosystems and human populations, particularly in coastal communities where environmental and health vulnerabilities overlap.

As the planet continues to warm and atmospheric CO₂ concentrations surpass 450 parts per million—levels not seen in millions of years—the interconnected fate of humans and coral reefs may serve as a powerful reminder that environmental health and human health are deeply intertwined. Understanding these shared vulnerabilities, the researchers say, is not only a scientific imperative but a public health necessity.