Enhanced Rates of Regional Warming and Ocean Acidification After Termination of Large‐Scale Ocean Alkalinization

Abstract

Termination effects of large‐scale artificial ocean alkalinization (AOA) have received little attention because AOA was assumed to pose low environmental risk. With the Max Planck Institute Earth system model, we use emission‐driven AOA simulations following the Representative Concentration Pathway 8.5 (RCP8.5). We find that after termination of AOA warming trends in regions of the Northern Hemisphere become ∼50% higher than those in RCP8.5 with rates similar to those caused by termination of solar geoengineering over the following three decades after cessation (up to 0.15 K/year). Rates of ocean acidification after termination of AOA outpace those in RCP8.5. In warm shallow regions where vulnerable coral reefs are located, decreasing trends in surface pH double (0.01 units/year) and the drop in the carbonate saturation state (Ω) becomes up to 1 order of magnitude larger (0.2 units/year). Thus, termination of AOA poses higher risks to biological systems sensitive to fast‐paced environmental changes than previously thought.

Carbonate Dissolution Enhanced by Ocean Stagnation and Respiration at the Onset of the Paleocene‐Eocene Thermal Maximum

“…During the early Paleogene, radiative forcing by CO 2 deviates significantly from pure logarithmic behavior, as it is assumed for modern conditions (Caballero & Huber, 2013;González et al, 2018). According to these studies, the climate sensitivity during the Paleocene-Eocene epoch was most probably higher than today's.…”

“…There is growing scientific evidence that climate sensitivity increases in warmer climates due to a strengthening of the water vapor feedback with increasing surface temperatures (Meraner et al, ; Popp et al, ). During the early Paleogene, radiative forcing by CO 2 deviates significantly from pure logarithmic behavior, as it is assumed for modern conditions (Caballero & Huber, ; González et al, ). According to these studies, the climate sensitivity during the Paleocene‐Eocene epoch was most probably higher than today's.…”

Tracking Improvement in Simulated Marine Biogeochemistry Between CMIP5 and CMIP6

“…Consequently, they have helped determine the change in carbon budgets that is compatible with a given level of warming since pre-industrial times. Ocean biogeochemical models have also been used to investigate potential geoengineering solutions to climate change such as solar radiation management [37][38][39], ocean fertilization [40][41][42][43][44][45][46][47], alkalinity addition [48][49][50][51][52] and reversibility experiments (e.g. [53,54]).…”

Detectability of Artificial Ocean Alkalinization and Stratospheric Aerosol Injection in MPI‐ESM

“…In the AOA scenario, atmospheric CO 2 concentrations are designed to follow the RCP4.5 trajectory, while the CO 2 emissions increase according to RCP8.5 (González & Ilyina, 2016; González et al, 2018). The cumulative emissions of the RCP8.5 scenario are 910 GtC larger than those of the RCP4.5 scenario.…”

“…In this study, only single‐model estimates of the externally forced response based on experiments run with the state‐of‐the‐art, Max Planck Institute Earth System Model (MPI‐ESM; González & Ilyina, 2016; González et al, 2018; Sonntag et al, 2018) are considered. Moreover, single‐model estimates of internal variability provided by the Max Planck Institute Grand Ensemble (MPI‐GE; Maher et al, 2019) are used to avoid potential biases that may be related to the sampling uncertainty of internal variability in the CMIP5 database.…”