A groundbreaking study from researchers at the University of Gothenburg has shed new light on the sources of rising atmospheric carbon dioxide levels following the last ice age. Traditionally, scientists have attributed the increase in carbon dioxide during the transition from glacial to interglacial periods primarily to changes in oceanic carbon storage. However, this new research suggests that thawing permafrost on northern lands played a far more significant role than previously recognized. The implications of this revelation deepen our understanding of Earth’s natural climate cycles and offer a crucial perspective on how carbon reservoirs respond to warming.
For many decades, the cyclical ebb and flow of atmospheric CO₂ concentrations have been linked closely with the global climate changes between ice ages and interglacial intervals. In these transitions, atmospheric carbon dioxide levels have been observed to climb roughly 100 parts per million as the climate warmed. The prevailing scientific explanation hinged on the oceans: colder oceans absorb more carbon, while warmer, more stratified oceans hold less, releasing CO₂ to the atmosphere during warming phases. While this ocean-centric view has dominated the discourse, the University of Gothenburg’s new meta-analysis challenges this paradigm by attributing nearly half of the post-glacial carbon dioxide increase to carbon emissions from thawing permafrost, particularly lands north of the Tropic of Cancer.
Permafrost — permanently frozen ground found primarily in the high latitudes of the Northern Hemisphere — serves as a substantial carbon sink. During the last Ice Age, large quantities of organic carbon were sequestered in soils that remained frozen, effectively locking away carbon that had accumulated from plant matter and other biological materials. These frozen deposits often included layers of loess, wind-blown silt and mineral dust accumulated to depths of tens of meters, overlaying organic-rich soils and preserved under permafrost conditions. The cold temperatures inhibited microbial activity and decomposition, stabilizing vast carbon stocks in these frozen grounds. When temperatures increased during the transition out of the Ice Age, this permafrost thawed, releasing carbon back into the atmosphere through decomposition processes.
By employing detailed pollen analyses spanning approximately the last 21,000 years and integrating these data into sophisticated climate models, researchers reconstructed the historical vegetation patterns across the Northern Hemisphere. This approach allowed the team to estimate organic carbon content in soils over millennia by correlating vegetation types with carbon storage capacities. Sampling every millennium, the study mapped the dynamics of carbon exchange between soil and atmosphere in response to changing climatic conditions and biomes. This innovative methodology enabled a more precise quantification of carbon fluxes in regions covered by permafrost, substantially enhancing the resolution of paleoclimate carbon budgets.
The last glacial maximum, around 21,000 years ago, saw massive continental ice sheets blanketing northern latitudes, including all of Scandinavia and present-day Canada. Vast tracts of Siberia, parts of China, and central Europe experienced intense permafrost conditions. As the climate warmed during the period roughly between 17,000 and 11,000 years ago, these permafrost zones rapidly thawed. The thaw resulted in a sizeable release of carbon dioxide back into the atmosphere. Whereas earlier models primarily accounted for oceanic emissions, the inclusion of terrestrial permafrost emissions markedly improves alignment between observed and modeled atmospheric CO₂ concentration trends.
Critically, the study finds that carbon dioxide levels rose from approximately 180 ppm during the glacial maximum to about 270 ppm by the start of the Holocene epoch, the current geological period that began around 11,700 years ago. This change reflects a natural cycle regulated by interactions across atmosphere, ocean, and land systems. Interestingly, after this initial increase, CO₂ concentrations stabilized for millennia despite continued permafrost thaw, due in part to compensatory carbon uptake by expanding peatlands and newly available land exposed as ice sheets retreated. Peatlands, known for their exceptional carbon sequestration potential, played a pivotal role in offsetting emissions from thawing permafrost, highlighting the complexity of terrestrial carbon feedbacks.
While these natural carbon dynamics illustrate Earth’s resilience during past climate shifts, the current anthropogenic impact far exceeds these historical natural variations. Since the onset of the Industrial Revolution about 250 years ago, fossil fuel combustion has substantially increased atmospheric CO₂ levels from pre-industrial values of roughly 280 ppm to over 420 ppm today. This unprecedented rise is driven by the release of ancient carbon compounds buried deep underground, an entirely novel disturbance to Earth’s carbon cycle with no historical analogue. Moreover, ongoing global warming continues to accelerate the thawing of contemporary permafrost, raising concerns about exacerbating atmospheric carbon levels through additional positive feedback loops.
One of the study’s lead researchers, Amelie Lindgren, highlights the urgency of understanding the combined effects of permafrost thaw and diminishing land availability. Unlike the post-glacial period, when retreating ice sheets exposed new land for carbon sequestration and the expansion of peatlands mitigated emissions, current sea-level rise threatens to reduce available terrestrial carbon sinks. With shrinking land surface areas and rapidly thawing permafrost, future carbon emissions may no longer be balanced by natural carbon uptake, amplifying the risks associated with ongoing anthropogenic climate change. This finding underscores the fragility of Earth’s carbon balance under accelerated warming scenarios.
The research contributes a vital piece to the puzzle of paleoclimate carbon dynamics, demonstrating the significant role terrestrial carbon reservoirs in northern high latitudes have played historically and will continue to play in the future. By revising estimates of carbon sources and sinks during critical historical epochs, the findings improve predictive models essential for climate policy and mitigation strategies. They also emphasize the urgent need to monitor and manage permafrost regions carefully, as their degradation holds substantial consequences for the global carbon cycle and, consequently, climate stability.
This comprehensive analysis, published in the renowned journal Science Advances, utilized a meta-analytical approach, synthesizing data from diverse paleoecological and climatological studies. By integrating multiple lines of evidence—including biological proxies like pollen, geochemical indicators, and climate simulations—the study achieves a robust, interdisciplinary understanding of the complex interactions shaping Earth’s historical atmospheric composition. The research sets a new standard for combining empirical data and modeling techniques to unravel Earth’s intricate climate history.
In conclusion, the unexpected magnitude of carbon emissions from thawing permafrost since the last ice age fundamentally reshapes our understanding of natural carbon cycle variability. It provides critical context for comprehending current and future anthropogenically driven changes in atmospheric greenhouse gases. As permafrost continues to thaw under modern warming, studying these natural precedents offers invaluable insights into potential feedback mechanisms and highlights the pressing need for urgent climate action to avoid triggering irreversible carbon release from Earth’s frozen reservoirs.
Subject of Research: Carbon cycle dynamics and sources of atmospheric CO₂ variations since the last ice age.
Article Title: Massive losses and gains of northern land carbon stocks since the Last Glacial Maximum
News Publication Date: 29-Aug-2025
Web References: http://dx.doi.org/10.1126/sciadv.adt6231
Image Credits: Boris Radosavljevic
Keywords: Permafrost, Carbon cycle, Ice age, Interglacial period, Atmospheric CO₂, Paleoclimate, Soil carbon, Peatlands, Climate change, Last Glacial Maximum, Carbon emissions, Northern Hemisphere
