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Abstract The recent sea ice changes in the Northern Hemisphere (NH), necessitate elucidating the sea ice variability over the past 2.6 million years (Ma), when the Earth’s glacial cycles transitioned from ∼41 to ∼100 kyr periodicity, following the Mid-Pleistocene Transition (MPT) period (0.7–1.2 Ma). Here, we analyze a coupled general circulation model (CGCM) simulation to understand how the NH sea ice responds to changes in the transient orbital, greenhouse gas (GHG), and ice-sheet forcings. We find that the Earth’s axial tilt (obliquity) and axial wobble (precession) strongly influence the variability in high-latitude (>70° N) perennial sea ice and mid-latitude (35° N–70° N) seasonal sea ice, respectively, by modifying the net surface shortwave radiation. Meanwhile, the GHG forcing affects the glacial–interglacial sea ice predominantly in the Labrador Sea, Irminger–Iceland basin sector, and Central North Pacific regions during the MPT and post-MPT (0.0–0.7 Ma) periods by modulating the downwelling longwave radiation. Additionally, we confirm that variability with longer periodicity (∼100 kyr) from GHG and ice-sheet forcings is most pronounced in NH sea ice during the MPT and post-MPT periods.

The original article can be found online at https://doi.org/10.1038/s41467-024-54339-2.Correction to:Nature Communicationshttps://doi.org/10.1038/s41467-024-54339-2, published online 19 November 2024In the Acknowledgements in this article, the grant number 'NRF-2022M3I6A108599' should have read 'NRF-2022M3I6A1085990'. The original article has been updated.By Hyo-Jeong Kim; Jin-Soo Kim; Soon-Il An; Jongsoo Shin; Ji-Hoon Oh and Jong-Seong KugReported by Author; Author; Author; Author; Author; Author [Extracted from the article]

The loss of ecosystem carbon (the sum of vegetation, litter, and soil carbon) may occur in a permafrost region under mitigation pathways, which could reduce the efficiency of carbon dioxide removal. Here, we investigate changes in permafrost under net-zero and negative emissions, based on idealized emission-driven simulations using a state-of- the- art Earth system model. While acting as a net ecosystem carbon sink during most of the positive emission phase, permafrost becomes a net ecosystem carbon source just before reaching net-zero and negative emissions. Permafrost slowly recovers, especially in regions with high organic carbon content, and net ecosystem carbon loss persists until the end of simulations, resulting in a cumulative net ecosystem carbon loss of approximately 14 petagrams of carbon (PgC) in both scenarios. In addition, methane emissions increase under net-zero and negative emissions, due to the irreversibility of the inundated areas. We conclude that the permafrost ecosystem carbon loss may continue under net-zero and negative emissions, which could hinder climate change mitigation efforts. [ABSTRACT FROM AUTHOR]