Impacts of North American forest cover changes on the North Atlantic Ocean circulation
| Title: | Impacts of North American forest cover changes on the North Atlantic Ocean circulation |
|---|---|
| Authors: | V. M. Bauer, S. Schemm, R. Portmann, J. Zhang, G. K. Eirund, S. J. De Hertog, J. Zibell |
| Source: | Earth System Dynamics, Vol 16, Pp 379-409 (2025) |
| Publisher Information: | Copernicus Publications, 2025. |
| Publication Year: | 2025 |
| Collection: | LCC:Science LCC:Geology LCC:Dynamic and structural geology |
| Subject Terms: | Science, Geology, QE1-996.5, Dynamic and structural geology, QE500-639.5 |
| More Details: | Planetary-scale forestation has been shown to induce global surface warming associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). This AMOC slowdown is accompanied by a negative North Atlantic sea surface temperature (SST) anomaly resembling the known North Atlantic warming hole found in greenhouse gas forcing simulations. Likewise, a reversed equivalent of the SST response has been found across deforestation experiments. Here, we test the hypothesis that localised forest cover changes over North America are an important driver of this response in the downstream North Atlantic Ocean. Moreover, we shine a light on the physical processes linking forest cover perturbations to ocean circulation changes. To this end, we perform simulations using the fully coupled Earth system model CESM2, where pre-industrial vegetation-sustaining areas over North America are either completely forested (“forestNA”) or turned into grasslands (“grassNA”). Our results show that North American forest cover changes have the potential to alter the AMOC and North Atlantic SSTs in a manner similar to global ones. North American forest cover changes mainly impact the ocean circulation through modulating land surface albedo and, subsequently, air temperatures. We find that comparably short-lived cold-air outbreaks (CAOs) play a crucial role in transferring the signal from the land to the ocean. Around 80 % of the ocean heat loss in the Labrador Sea occurs within CAOs during which the atmosphere is colder than the underlying ocean. A warmer atmosphere in forestNA compared to the “control” scenario results in fewer CAOs over the ocean and thereby reduced ocean heat loss and deep convection, with the opposite being true for grassNA. The induced SST responses further decrease CAO frequency in forestNA and increase it in grassNA. Lagrangian backward trajectories starting from CAOs over the Labrador Sea confirm that their source regions include (de-)forested areas. Furthermore, the subpolar gyre circulation is found to be more sensitive to ocean density changes driven by heat fluxes than to changes in wind forcing modulated by upstream land surface roughness. In forestNA, sea ice growth and the corresponding further reduction in ocean-to-atmosphere heat fluxes forms an additional positive feedback loop. Conversely, a buoyancy flux decomposition shows that freshwater forcing only plays a minor role in the ocean density response in both scenarios. Overall, this study shows that the North Atlantic Ocean circulation is particularly sensitive to upstream forest cover changes and that there is a self-enhancing feedback between CAO frequencies, deep convection, and SSTs in the North Atlantic. This motivates studying the relative importance of these high-frequency atmospheric events for ocean circulation changes in the context of anthropogenic climate change. |
| Document Type: | article |
| File Description: | electronic resource |
| Language: | English |
| ISSN: | 2190-4979 2190-4987 |
| Relation: | https://esd.copernicus.org/articles/16/379/2025/esd-16-379-2025.pdf; https://doaj.org/toc/2190-4979; https://doaj.org/toc/2190-4987 |
| DOI: | 10.5194/esd-16-379-2025 |
| Access URL: | https://doaj.org/article/07a93badaf40490f88516112351cc2f6 |
| Accession Number: | edsdoj.07a93badaf40490f88516112351cc2f6 |
| Database: | Directory of Open Access Journals |
| ISSN: | 21904979 21904987 |
|---|---|
| DOI: | 10.5194/esd-16-379-2025 |
| Published in: | Earth System Dynamics |
| Language: | English |