A groundbreaking study published today in the European Geosciences Union (EGU) journal Earth System Dynamics reveals a critical and previously underestimated connection between Antarctic sea ice, cloud cover, and global warming. This research highlights that the current extent of Antarctic sea ice, which exceeds climate model predictions, suggests more significant global warming in the coming decades.
The study, led by Linus Vogt from Sorbonne University, utilized an emergent constraint based on data from 28 Earth system models and satellite observations spanning 1980 to 2020. This approach allowed the team to reduce uncertainty in climate projections and provide improved estimates of key climate variables. Their findings indicate that ocean heat uptake and the resulting thermal sea level rise by 2100 are projected to be 3–14% higher than the average from CMIP6, a leading collection of climate models. Furthermore, the projected cloud feedback is 19–31% stronger, leading to enhanced climate sensitivity and an estimated global surface warming increase of 3–7% compared to previous predictions.
Understanding the Antarctic Sea Ice Connection
The study found that the extent of Antarctic summer sea ice, previously considered stable and weakly connected to human-caused climate change, is a crucial indicator of the Southern Hemisphere’s climate. Models that begin with a higher, more accurate representation of pre-industrial sea ice levels simulate colder surface waters, colder deep ocean temperatures, and thicker cloud cover in the mid-latitudes. These initial conditions amplify warming responses under greenhouse gas forcing, resulting in a more severe and accelerated warming effect than previously estimated. Essentially, the climate system’s starting point increases its sensitivity to greenhouse gases.
“When we initially discovered this link between historical Antarctic sea ice and future global ocean heat uptake, we were surprised by the strength of the relationship. Antarctic sea ice covers less than 4% of the ocean’s surface, so how could it be so strongly associated with global ocean warming?” says Linus Vogt, who led the study at Sorbonne University in Paris, and is now based at New York University.
This relationship is not merely correlative but is mechanistically explained through ocean-atmosphere feedback. Higher sea ice extent enhances cloud cover, which has an overall cooling effect by reducing incoming solar radiation. Greater sea ice loss in the coming decades is thus linked to larger reductions of clouds, stronger surface warming, and enhanced ocean heat uptake. As a result, the baseline state of sea ice and deep ocean temperatures in models effectively preconditions the magnitude of warming, cloud feedback, and heat uptake in the future.
Implications for Climate Projections and Policy
According to Jens Terhaar, a senior scientist at the division of Climate and Environmental Physics at the University of Bern, “While it has long been known that accurately representing clouds is crucial for climate projections, our study highlights that it is equally important to also accurately simulate the surface and deep ocean circulation and its interaction with sea ice.”
Under future climate change scenarios, models with greater historical sea ice tend to lose more sea ice by 2100, contributing to stronger radiative feedback. This stronger feedback leads to more intense atmospheric and oceanic warming, particularly across the Southern Hemisphere.
This study provides evidence that current models may be underestimating future warming and ocean heat storage. It shows that models tend to simulate a too warm Southern Ocean in the preindustrial state and therefore have too little warming potential. The findings also stress the importance of continued satellite monitoring and improved modeling of cloud processes and deep ocean hydrography, both of which significantly shape global climate projections.
Reevaluating Climate Models and Future Actions
The study warns that previous approaches, which relied on observed trends over limited timeframes, may have underestimated future warming due to their inability to capture systemic changes, or ‘regime shifts,’ that are now becoming more evident, such as the record-low Antarctic sea ice extent in 2023. Furthermore, these older constraint methods relied on trends over short historical windows (e.g., 1980–2015), which are sensitive to internal natural variability and may not represent future climate change accurately.
“Several high-profile studies have used temperature trends over recent decades in an attempt to constrain future warming,” says Vogt. “However, we now found that this approach can give misleading results. Accounting for the sea ice-related mechanism we identified leads to increased estimates of future ocean and atmospheric warming. This likely stronger warming calls for urgent action to reduce greenhouse gas emissions in order to avoid the increased heat waves, floods, and ecosystem impacts associated with ocean warming.”
The announcement comes as the world grapples with the impacts of climate change, underscoring the urgency for policymakers to incorporate these findings into climate strategies. The study’s insights could reshape how future climate models are developed, emphasizing the need for a holistic approach that considers the intricate interactions between sea ice, ocean, and atmosphere.
About the EGU: The European Geosciences Union (EGU) is Europe’s premier geosciences union, dedicated to the pursuit of excellence in the Earth, planetary, and space sciences for the benefit of humanity, worldwide. It is a non-profit interdisciplinary learned association of scientists founded in 2002 with headquarters in Munich, Germany. The EGU publishes a number of diverse scientific journals that use an innovative open access format and organizes topical meetings plus education and outreach activities. Its annual General Assembly is the largest and most prominent European geosciences event, attracting more than 20,000 scientists from all over the world. The meeting’s sessions cover a wide range of topics, including volcanology, planetary exploration, the Earth’s internal structure and atmosphere, climate, energy, and resources.
