New research shows that the global costs associated with the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) may exceed previous estimates. The study found that the weakening of the AMOC reduces the ability of the oceans to absorb carbon, leading to higher atmospheric CO\u2082 concentrations and more intense global warming. This AMOC carbon cycle feedback, when factored into an integrated climate-economic model, causes additional economic damage worth several trillion US dollars and increases the social cost of carbon (SCC) by about 1 %.<\/p>\n
What is AMOC and why is it important?<\/strong><\/p>\n The Atlantic Meridional Overturning Circulation (AMOC) is a large-scale system of ocean currents that transports warm water from the tropics to the North Atlantic and cold water back to the southern regions. This system is crucial for regulating global climate, influencing temperature and weather patterns around the world. A weakening of the AMOC could have serious consequences, including widespread cooling in the Northern Hemisphere, changes in precipitation, rising sea levels, and disruptions to the carbon cycle.<\/p>\n How does the weakening of the AMOC affect the carbon cycle?<\/strong><\/p>\n The North Atlantic currently absorbs a large portion of anthropogenic CO\u2082, allowing the AMOC to transport dense, carbon-rich water masses from the surface to the deep ocean. As a result of global warming, the AMOC is expected to weaken, reducing the ocean's ability to absorb atmospheric carbon. This results in more CO\u2082 remaining in the atmosphere, further increasing global warming. This process is referred to as the AMOC carbon feedback.<\/p>\n Key findings of the study<\/strong><\/p>\n \u2013 Simulations reveal an approximately linear relationship between AMOC strength and reduction in carbon uptake.<\/p>\n \u2013 By the end of the modeling period, AMOC weakening leads to changes in ocean carbon storage of more than 30 PgC for the 1pct experiment and more than 15 PgC for the SSP2-4.5 scenario.<\/p>\n \u2013 Projections show that the AMOC will weaken by 20 to 50 % by the end of the century. This weakening will reduce ocean carbon storage by 3.9 to 12.4 PgC in 2100.<\/p>\n \u2013 Including the AMOC carbon feedback in the integrated assessment model leads to additional damages worth several trillion US dollars and increases the SCC by approximately 1 %.<\/p>\n \u2013 The effects of the SCC carbon feedback of the AMOC are similar but opposite to the effects of AMOC-induced surface cooling.<\/p>\n \u2013 The economic importance of the AMOC carbon feedback is growing as the world moves towards limiting global warming to internationally agreed levels.<\/p>\n Modeling methods<\/strong><\/p>\n The study uses a large-scale modeling approach that combines Earth system simulations with an integrated assessment model. The MPI-ESM model is used to simulate climate states with an artificially weakened AMOC. The resulting changes in annual ocean carbon storage are then analyzed as a function of the simulated AMOC, leading to a quantitative relationship between AMOC strength and changes in carbon fluxes. AMOC projections from CMIP6 models are used to estimate the strength of the AMOC carbon feedback to 2100 under the SSP2-4.5 scenario. The economic impact of these projected changes is then analyzed in META IAM by calculating the relative change in SCC that results from explicitly incorporating the AMOC carbon feedback into the model structure.<\/p>\n Implications for policymaking<\/strong><\/p>\n The study\u2019s findings have important implications for climate policymaking. The social cost of carbon (SCC) is an important economic indicator of the impact of climate change, quantifying the economic cost per additional ton of CO\u2082 emitted. It is increasingly being used by governments and organizations around the world to inform climate policies and investment decisions. The study highlights that current SCC estimates may not fully capture all the economic costs associated with AMOC slowdowns, particularly the impact on ocean carbon absorption. Including these costs in SCC models could lead to stricter climate policies and increased efforts to reduce greenhouse gas emissions.<\/p>\n Limitations and future research<\/strong><\/p>\n The authors acknowledge that their study has some limitations. The estimates of AMOC-induced carbon flux changes are based on simulations with the MPI-ESM model. Some aspects of ocean and carbon cycle dynamics would likely differ in equivalent simulations with other Earth System Models (ESMs). The economic impact estimate is subject to uncertainties, as well as normative and structural modeling decisions. However, the authors note that the larger body of model evidence from the CMIP6 carbon feedback experiments, as well as other model-based studies, yields similar results, increasing confidence in the dynamics and scale of their findings.<\/p>\n The authors emphasize that their results should not be interpreted as a definitive estimate of the impact of AMOC weakening, but rather as a step on a long journey to assess the full economic consequences of this phenomenon. They highlight the need for further research to examine other potential impacts of AMOC weakening, such as changes in precipitation, sea level, or North Atlantic storm tracks.<\/p>\n The study provides valuable insights into the potential economic consequences of AMOC weakening. It highlights that the reduction in the oceans' ability to absorb carbon due to AMOC weakening could have significant economic costs that are currently not accounted for in standard assessments. Including these costs in SCC models could lead to more stringent climate action and increased efforts to reduce greenhouse gas emissions. Spring<\/strong><\/em><\/p>\n