<(From Left) Professor Haewon McJeon, Dr. Paul Wolfram>
Earth is not infinite. Pollution beyond certain levels threatens the climate and ecosystems. To prevent this, scientists have proposed "Planetary Boundaries," defining the safe operating limits of the Earth system. A KAIST research team recalculated climate change and nitrogen pollution using the same standard and found that current carbon emissions already exceed the planet's sustainable limit by more than double.
KAIST (President Kwang Hyung Lee) announced on the 6th of March that Professor Haewon McJeon of the Graduate School of Green Growth and Sustainability, in collaboration with Dr. Paul Wolfram's team at the Pacific Northwest National Laboratory (PNNL) of the U.S. Department of Energy, recalculated the carbon dioxide emission boundary using an annual emissions (flow) framework rather than the traditional cumulative carbon stock framework.
Until now, climate change has been evaluated based on how much CO₂ accumulates in the atmosphere (stock). In contrast, nitrogen and phosphorus pollution have been assessed based on how much is emitted each year (flow). Because these problems were measured using different metrics, it was difficult to fairly compare their relative severity. The research team therefore recalculated carbon emissions using the same annual emissions framework used for nitrogen pollution.
Based on the condition of limiting the rise in global average temperature to within 1.5°C, the analysis showed that the Earth's safe limit for annual CO₂ emissions is approximately 4–17 gigatons (Gt CO₂ per year). However, humanity's current annual emissions amount to about 37 gigatons (Gt CO₂ per year). This level exceeds the Earth's safe operating space by more than twofold.
Professor Haewon McJeon stated, "When carbon emissions are compared using the same framework as nitrogen pollution, the severity of climate change becomes much clearer," adding, "This study helps place different environmental problems on the same analytical basis, which can contribute to setting clearer policy priorities."
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He further emphasized, "The need for integrated strategies that simultaneously consider carbon, nitrogen, and phosphorus pollution is growing," adding that global efforts toward decarbonization must accelerate further.
The study was jointly led by Professor Haewon McJeon and Dr. Paul Wolfram as co-corresponding authors, with Hassan Niazi, Page Kyle, and other researchers from PNNL participating as collaborators. The research results were published on February 16 in the international journal Nature Sustainability.
※ Paper title: "Ensuring consistency between biogeochemical planetary boundaries"
DOI: https://doi.org/10.1038/s41893-026-01770-6
This research was supported by the project "Development of an AI-Based Next-Generation Integrated Assessment Model for Climate–Human Interactions" funded by the Ministry of Science and ICT and the National Research Foundation of Korea.
In a Science commentary published on March 5 titled "Thirty-six solutions to stabilize Earth's climate," Professor McJeon revisited the progress of climate technologies over the past 20 years. He pointed out that although humanity has possessed many of the necessary technologies, they have not been implemented quickly enough, allowing the climate crisis to intensify. He also emphasized that the pace of decarbonization must accelerate to achieve carbon neutrality.
※ Commentary: "Thirty-six solutions to stabilize Earth's climate"
Link: https://doi.org/10.1126/science.aed5212
