Despite the adoption of the Paris Agreement ten years ago, fossil CO2 emissions continue to rise, pushing atmospheric CO2 levels to 423 ppm in 2024 and driving human-induced warming to 1.36°C, within years of breaching the 1.5°C limit 1,2. Accurate reporting of anthropogenic and natural CO2 sources and sinks is a prerequisite to tracking the effectiveness of climate policy and detecting carbon sink responses to climate change. Yet notable mismatches between reported emissions and sinks have so far prevented confident interpretation of their trends and drivers 1. Here, we present and integrate recent advances in observations and process understanding to address some long-standing issues in the global carbon budget estimates. We show that the magnitude of the natural land sink is substantially smaller than previously estimated, while net emissions from anthropogenic land-use change are revised upwards 1. The ocean sink is 15% larger than the land sink, consistent with new evidence from oceanic and atmospheric observations 3,4. Climate change reduces the efficiency of the sinks, particularly on land, contributing 8.3 ± 1.4 ppm to the atmospheric CO2 increase since 1960. The combined effects of climate change and deforestation turn Southeast Asian and large parts of South American tropical forests from CO2 sinks to sources. This underscores the need to halt deforestation and limit warming to prevent further loss of carbon stored on land. Improved confidence in assessments of CO2 sources and sinks is fundamental for effective climate policy.

Contact: Dr. Shouting Tuo State Key Laboratory of Marine Geology Tongji University 1239 Siping Road, Shanghai 200092, China Email: [email protected], Tel.: +86-21-6598 2198

PAGES Shanghai 2025