Researchers at the University of California, Riverside have identified a crucial missing element in the Earth’s carbon recycling process, suggesting that global warming might inadvertently lead to a new ice age. This groundbreaking study challenges the conventional understanding of Earth’s climate regulation, which has long been attributed to the slow but steady process of rock weathering.
Traditionally, scientists believed that Earth’s climate stability was maintained by rain capturing carbon dioxide from the atmosphere. This rainwater then interacts with exposed rocks, particularly silicate rocks like granite, gradually dissolving them. The dissolved carbon, along with calcium, eventually reaches the ocean, where it forms seashells and limestone reefs, effectively sequestering carbon on the sea floor for millions of years.
“As the planet gets hotter, rocks weather faster and take up more CO₂, cooling the planet back down again,” explained Andy Ridgwell, a UCR geologist and co-author of the study published in Science.
Revisiting Geological History
However, geological evidence reveals that past ice ages were so severe that they enveloped the entire planet in snow and ice. This indicates that the gentle regulation of planetary temperature through rock weathering alone cannot account for such extreme climate events.
The researchers propose that the missing link involves carbon burial in the ocean. As atmospheric CO₂ levels rise and the planet warms, more nutrients, such as phosphorus, are washed into the sea. These nutrients stimulate plankton growth, which absorbs carbon dioxide during photosynthesis. When plankton dies, it sinks to the ocean floor, sequestering carbon with it.
Yet, in a warmer climate with increased algal activity, oceans lose oxygen, causing phosphorus to be recycled rather than buried. This creates a feedback loop: more nutrients lead to more plankton, whose decay further depletes oxygen, allowing even more nutrients to be recycled. Simultaneously, significant amounts of carbon are buried, cooling the Earth.
The Overshoot Effect
This process doesn’t merely stabilize the climate; it overshoots, cooling Earth significantly below its initial temperature. In the study’s computer model, this mechanism could potentially trigger an ice age.
Ridgwell likens this phenomenon to a thermostat working overtime to cool a house. “In summer, you set your thermostat around 78°F. As the air temperature climbs outside during the day, the air conditioning removes the excess heat inside until the room temperature comes down to 78 and then it stops,” Ridgwell explained.
In his analogy, Earth’s thermostat isn’t malfunctioning, but it might not be optimally placed, akin to having the thermostat in a different room from the air conditioning unit, leading to uneven performance.
Historical Parallels and Future Implications
In the geological past, lower atmospheric oxygen levels made Earth’s climate regulation system much more erratic, resulting in ancient extreme ice ages. Today, as humans continue to add CO₂ to the atmosphere, the planet is expected to warm in the short term. However, the researchers’ model predicts a cooling overshoot will occur. This time, it is expected to be milder due to the higher oxygen levels in the atmosphere, which dampen the nutrient feedback loop.
“Like placing the thermostat closer to the AC unit,” Ridgwell added. Despite this, it could still be enough to hasten the onset of the next ice age.
Looking Ahead
Ridgwell raises a critical question: “At the end of the day, does it matter much if the start of the next ice age is 50, 100, or 200 thousand years into the future?” He emphasizes the urgent need to focus on limiting current warming trends. The eventual cooling of Earth, no matter how erratic, will not occur swiftly enough to mitigate the immediate impacts of climate change in our lifetime.
This discovery underscores the complexity of Earth’s climate systems and the potential long-term consequences of human-induced warming. As scientists continue to unravel these intricate processes, the study serves as a reminder of the delicate balance that governs our planet’s climate and the importance of sustainable environmental practices.
