Terhaar
Jens
Terhaar
Jens
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ArticleOcean acidification in emission-driven temperature stabilization scenarios: the role of TCRE and non-CO2 greenhouse gases(IOP Publishing, 2023-02-02) Terhaar, Jens ; Frölicher, Thomas L. ; Joos, FortunatFuture ocean acidification mainly depends on the continuous ocean uptake of CO2 from the atmosphere. The trajectory of future atmospheric CO2 is prescribed in traditional climate projections with Earth system models, leading to a small model spread and apparently low uncertainties for projected acidification, but a large spread in global warming. However, climate policies such as the Paris Agreement define climate targets in terms of global warming levels and as traditional simulations do not converge to a given warming level, they cannot be used to assess uncertainties in projected acidification. Here, we perform climate simulations that converge to given temperature levels using the Adaptive Emission Reduction Algorithm (AERA) with the Earth system model Bern3D-LPX at different setups with different Transient Climate Response to cumulative carbon Emissions (TCRE) and choices between reductions in CO2 and non-CO2 forcing agents. With these simulations, we demonstrate that uncertainties in surface ocean acidification are an order of magnitude larger than the usually reported inter-model uncertainties from simulations with prescribed atmospheric CO2. Uncertainties in acidification at a given stabilized temperature are dominated by TCRE and the choice of emission reductions of non-CO2 greenhouse gases (GHGs). High TCRE and relatively low reductions of non-CO2 GHGs, for example, necessitate relatively strong reductions in CO2 emissions and lead to relatively little ocean acidification at a given temperature level. The results suggest that choices between reducing emissions of CO2 versus non-CO2 agents should consider the economic costs and ecosystem damage of ocean acidification.
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ArticleMagnitude, trends, and variability of the global ocean carbon sink from 1985‐2018(American Geophysical Union, 2023-09-11) DeVries, Tim ; Yamamoto, Kana ; Wanninkhof, Rik ; Gruber, Nicolas ; Hauck, Judith ; Muller, Jens Daniel ; Bopp, Laurent ; Carroll, Dustin ; Carter, Brendan ; Chau, Thi-Tuyet-Trang ; Doney, Scott C. ; Gehlen, Marion ; Gloege, Lucas ; Gregor, Luke ; Henson, Stephanie A. ; Kim, Ji-Hyun ; Iida, Yosuke ; Ilyina, Tatiana ; Landschutzer, Peter ; Le Quere, Corinne ; Munro, David R. ; Nissen, Cara ; Patara, Lavinia ; Perez, Fiz F. ; Resplandy, Laure ; Rodgers, Keith B. ; Schwinger, Jorg ; Seferian, Roland ; Sicardi, Valentina ; Terhaar, Jens ; Trinanes, Joaquin ; Tsujino, Hiroyuki ; Watson, Andrew J. ; Yasunaka, Sayaka ; Zeng, JiyeThis contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation-based products. The mean sea-air CO2 flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr−1 based on an ensemble of reconstructions of the history of sea surface pCO2 (pCO2 products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at −2.1 ± 0.3 PgC yr−1 by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr−1 of terrestrially derived CO2, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO2 products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr−1 decade−1, while biogeochemical models and inverse models diagnose an anthropogenic CO2-driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr−1 decade−1, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO2-forced variability by 2–3 times. These results suggest that anthropogenic CO2 dominates the ocean CO2 sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.
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ArticleAn assessment of CO2 uptake in the Arctic Ocean from 1985 to 2018(American Geophysical Union, 2023-11-10) Yasunaka, Sayaka ; Manizza, Manfredi ; Terhaar, Jens ; Olsen, Are ; Yamaguchi, Ryohei ; Landschutzer, Peter ; Watanabe, Eiji ; Carroll, Dustin ; Adiwira, Hanani ; Muller, Jens Daniel ; Hauck, JudithAs a contribution to the Regional Carbon Cycle Assessment and Processes phase 2 (RECCAP2) project, we present synthesized estimates of Arctic Ocean sea-air CO2 fluxes and their uncertainties from surface ocean pCO2-observation products, ocean biogeochemical hindcast and data assimilation models, and atmospheric inversions. For the period of 1985–2018, the Arctic Ocean was a net sink of CO2 of 116 ± 4 TgC yr−1 in the pCO2 products, 92 ± 30 TgC yr−1 in the models, and 91 ± 21 TgC yr−1 in the atmospheric inversions. The CO2 uptake peaks in late summer and early autumn, and is low in winter when sea ice inhibits sea-air fluxes. The long-term mean CO2 uptake in the Arctic Ocean is primarily caused by steady-state fluxes of natural carbon (70% ± 15%), and enhanced by the atmospheric CO2 increase (19% ± 5%) and climate change (11% ± 18%). The annual mean CO2 uptake increased from 1985 to 2018 at a rate of 31 ± 13 TgC yr−1 dec−1 in the pCO2 products, 10 ± 4 TgC yr−1 dec−1 in the models, and 32 ± 16 TgC yr−1 dec−1 in the atmospheric inversions. Moreover, 77% ± 38% of the trend in the net CO2 uptake over time is caused by climate change, primarily due to rapid sea ice loss in recent years. Furthermore, true uncertainties may be larger than the given ensemble standard deviations due to common structural biases across all individual estimates.
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ArticleThe Southern Ocean Carbon Cycle 1985–2018: Mean, Seasonal Cycle, Trends, and Storage(American Geophysical Union, 2023-11-10) Hauck, Judith ; Gregor, Luke ; Nissen, Cara ; Patara, Lavinia ; Hague, Mark ; Mongwe, Precious ; Bushinsky, Seth ; Doney, Scott C. ; Gruber, Nicolas ; Le Quere, Corinne ; Manizza, Manfredi ; Mazloff, Matthew R. ; Monteiro, Pedro M. S. ; Terhaar, JensWe assess the Southern Ocean CO2 uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2. The Southern Ocean acted as a sink for CO2 with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75 ± 0.28 PgC yr−1) and pCO2-observation-based products (0.73 ± 0.07 PgC yr−1). This sink is only half that reported by RECCAP1 for the same region and timeframe. The present-day net uptake is to first order a response to rising atmospheric CO2, driving large amounts of anthropogenic CO2 (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO2-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26 ± 0.06 and 0.11 ± 0.03 Pg C yr−1 decade−1, respectively). This is despite nearly identical pCO2 trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO2 was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push toward better process understanding of drivers of the carbon cycle.
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ArticleGlobal surface ocean acidification indicators from 1750 to 2100(American Geophysical Union, 2023-03-23) Jiang, Li-Qing ; Dunne, John ; Carter, Brendan R. ; Tjiputra, Jerry F. ; Terhaar, Jens ; Sharp, Jonathan D. ; Olsen, Are ; Alin, Simone ; Bakker, Dorothee C. E. ; Feely, Richard A. ; Gattuso, Jean-Pierre ; Hogan, Patrick ; Ilyina, Tatiana ; Lange, Nico ; Lauvset, Siv K. ; Lewis, Ernie R. ; Lovato, Tomas ; Palmieri, Julien ; Santana-Falcon, Yeray ; Schwinger, Joerg ; Seferian, Roland ; Strand, Gary ; Swart, Neil ; Tanhua, Toste ; Tsujino, Hiroyuki ; Wanninkhof, Rik ; Watanabe, Michio ; Yamamoto, Akitomo ; Ziehn, TiloAccurately predicting future ocean acidification (OA) conditions is crucial for advancing OA research at regional and global scales, and guiding society's mitigation and adaptation efforts. This study presents a new model-data fusion product covering 10 global surface OA indicators based on 14 Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), along with three recent observational ocean carbon data products. The indicators include fugacity of carbon dioxide, pH on total scale, total hydrogen ion content, free hydrogen ion content, carbonate ion content, aragonite saturation state, calcite saturation state, Revelle Factor, total dissolved inorganic carbon content, and total alkalinity content. The evolution of these OA indicators is presented on a global surface ocean 1° × 1° grid as decadal averages every 10 years from preindustrial conditions (1750), through historical conditions (1850–2010), and to five future Shared Socioeconomic Pathways (2020–2100): SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. These OA trajectories represent an improvement over previous OA data products with respect to data quantity, spatial and temporal coverage, diversity of the underlying data and model simulations, and the provided SSPs. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change and ocean acidification. The gridded data product is available in NetCDF at the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information: https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0259391.html, and global maps of these indicators are available in jpeg at: https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/synthesis/surface-oa-indicators.html.
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ArticleAssessment of global ocean biogeochemistry models for ocean carbon sink estimates in RECCAP2 and recommendations for future studies(American Geophysical Union, 2024-03-14) Terhaar, Jens ; Goris, Nadine ; Muller, Jens D. ; DeVries, Tim ; Gruber, Nicolas ; Hauck, Judith ; Perez, Fiz F. ; Seferian, RolandThe ocean is a major carbon sink and takes up 25%–30% of the anthropogenically emitted CO2. A state-of-the-art method to quantify this sink are global ocean biogeochemistry models (GOBMs), but their simulated CO2 uptake differs between models and is systematically lower than estimates based on statistical methods using surface ocean pCO2 and interior ocean measurements. Here, we provide an in-depth evaluation of ocean carbon sink estimates from 1980 to 2018 from a GOBM ensemble. As sources of inter-model differences and ensemble-mean biases our study identifies (a) the model setup, such as the length of the spin-up, the starting date of the simulation, and carbon fluxes from rivers and into sediments, (b) the simulated ocean circulation, such as Atlantic Meridional Overturning Circulation and Southern Ocean mode and intermediate water formation, and (c) the simulated oceanic buffer capacity. Our analysis suggests that a late starting date and biases in the ocean circulation cause a too low anthropogenic CO2 uptake across the GOBM ensemble. Surface ocean biogeochemistry biases might also cause simulated anthropogenic fluxes to be too low, but the current setup prevents a robust assessment. For simulations of the ocean carbon sink, we recommend in the short-term to (a) start simulations at a common date before the industrialization and the associated atmospheric CO2 increase, (b) conduct a sufficiently long spin-up such that the GOBMs reach steady-state, and (c) provide key metrics for circulation, biogeochemistry, and the land-ocean interface. In the long-term, we recommend improving the representation of these metrics in the GOBMs.