Irreversibility of Marine Climate Change Impacts Under Carbon Dioxide Removal

Abstract

Artificial carbon dioxide removal (CDR) from the atmosphere has been proposed as a measure for mitigating climate change and restoring the climate system to a target state after exceedance (“overshoot”). This research investigates to what extent overshoot and subsequent recovery of a given cumulative CO₂ emissions level by CDR leaves a legacy in the marine environment using an Earth system model. We use RCP2.6 and its extension to year 2300 as the reference scenario and design a set of cumulative emissions and temperature overshoot scenarios based on other RCPs. Our results suggest that the overshoot and subsequent return to a reference cumulative emissions level would leave substantial impacts on the marine environment. Although the changes in sea surface temperature, pH, and dissolved oxygen are largely reversible, global mean values and spatial patterns of these variables differ significantly from those in the reference scenario when the reference cumulative emissions are attained.

Plain Language Summary

Commitments by countries to reduce emissions of carbon dioxide (CO₂) fall short of what is needed to limit global warming to below 2°C, a goal of the Paris Agreement, creating a risk that the 2°C limit may be exceeded. Restoring global temperature to a target level after exceedance (“overshoot”) requires artificial carbon dioxide removal (CDR) from the atmosphere. Earlier studies showed that changes in surface air temperature can be reversed by CDR but climate variables that take longer to respond to changes in atmospheric CO₂ are slower to reverse. In this research we investigate to what extent the impacts of overshoot on the marine environment can be reversed with CDR. We show that the ocean responds slowly to a decrease in atmospheric CO₂ concentration by CDR, particularly for scenarios with large levels of overshoot. The overshoot results in substantial impacts on the marine environment for centuries with potentially detrimental effects for marine ecosystems.