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Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points

Periodic Reporting for period 1 - COMFORT (Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points)

Reporting period: 2019-09-01 to 2021-02-28

Human-induced forcing has instigated an unprecedentedly rapid and pervasive change of the Earth system and climate. Ocean biogeochemical climate is altered due to the progressing uptake of heat and CO2 (carbon dioxide) caused by human activity. The drivers include biogeochemical fluxes from land: river loads, atmospheric deposition, land-atmosphere greenhouse gas fluxes. Consequently, enhanced stratification, changes in global circulation, acidification, and loss of oxygen with the potential spreading of dead zones have already been observed globally. Additionally, ocean extreme events associated with these changes are expected to become more frequent and intense. Particularly dangerous are changes that, once a critical threshold or tipping point (TP) is reached due to external forcing, they accelerate strongly, and occur much faster than the rate of forcing. Past research has dealt mainly with Earth system tipping elements associated with low probability/high impact of risk events. In contract, COMFORT focuses on likelihood and quantification of ocean related high probability/high impact of risk tipping points, their impact on the wider Earth system, and provides the framework for taking optimal action to limit damage. The overall objective of COMFORT is to close knowledge gaps for key ocean tipping elements within the Earth system under anthropogenic physical and chemical climate forcing through a coherent interdisciplinary research approach. The project aims to provide added value to decision and policy makers in terms of safe marine operating spaces, climate mitigation targets, and feasible mitigation pathways. It focuses on the triple threat of (1) warming, (2) deoxygenation, and (3) ocean acidification, and how to optimally deal with it.

The following specific objectives are addressed (CT=core theme, WP= work package; Figure):
1. Identify climate-induced ocean TPs and attribute them to processes (CT1, WPs 1-2).
2. Quantify related impacts and establish multi-dimensional safe operating spaces (SOS) (CT2, WPs 3-4).
3. Provide respective mitigation targets and options, as well as projected mitigation pathways (CT3, WPs 5-6).
4. Integrate stakeholder knowledge and provide new results including data to users (CT4, WPs 7-10).
Within CT1, a new global comprehensive dataset of physical and biogeochemical ocean data over the historical period was compiled. Also, major screenings of TPs along with insights into the dynamics of TPs and abrupt changes have been carried out by employing Earth System model (ESM) simulations and observational datasets. COMFORT results show that under continued global warming, it is expected that the Arctic Ocean primary production will become less light-limited due to sea ice retreat, but more nutrient limited through increased Pacific-Arctic-Atlantic connectivity. Also, warming and acidification signals of the North Atlantic will be injected ‘rapidly’ into the Arctic Ocean representing the primary mechanism of Arctic warming and acidification. Furthermore, COMFORT results show that the frequency of large and impactful marine heatwaves has already increased more than 20-fold due to global warming. Additionally, acidity extremes and compound events will become more frequent and intense under continued climate change with detrimental impacts on marine ecosystems.

In CT2, a significant progress was made on TP case studies to assess the impacts, risks, and thresholds for habitat conditions, ecosystem changes, and fisheries under projected changes of key physical and chemical forcings . This work provided the definition of ecoregions, and the identification of ecological niches of benthic mesophotic communities from present conditions. Also, a bleaching susceptibility map and an indicator for the risk of coral bleaching in the Indian Ocean have been formed. Modelling studies of tuna species provided an estimation of the climate change impact on the tuna stock in the Pacific and further impact on the economy of small Pacific Islands States that heavily depend on this resource. Furthermore, the diverse fish stocks data was analysed to explore if climate induced TPs cascade to food webs and higher trophic levels. A first quantitative test of the SOS approach was conducted which will allow the assessment of revised mitigation scenarios.

A comprehensive assessment of mitigation options and targets has been initiated in CT3. First, a list of target variables and metrics to evaluate future projection and SOS has been developed. Currently, the contribution and risks of marine technical mitigation measures to achieve low greenhouse gas emission scenarios is being assessed, including carbon removal scenarios.

In CT4, the Stakeholder Reference Group (SRG) consisting of members from complementary domains and a two-way communication have been established. Additionally, the project results have been formatted with interoperable access to all users and all scientific publications are publicly available. Externally, COMFORT scientists have promoted the new results through their roles in international assessments and strategic documents.
COMFORT made progress beyond the start-of-the-art. New evidence on oceanic abrupt changes, their location and timing, and their dynamics have been provided using a variety of methods and contributing to the respective scientific literature through peer-reviewed publications. New ways to analyse the impact of climate change and ocean acidification on marine living resources have been developed and are now applied. Progress has also been made concerning compilations of environmental ecosystem thresholds and mitigation targets. New Earth system model runs have been carried out including runs on carbon dioxide removal and selected re-runs with storage of results at high time resolution. A huge new observational data sets on ocean biogeochemistry has been compiled and is currently made available for the scientific community.

The knowledge on marine tipping points and the new tools will be key for designing optimal mitigation pathways concerning emission scenarios and additional mitigation measures. Expected results will be further substantial additions to the scientific literature on abrupt oceanic change with respect to physics, biogeochemistry, and ecosystems. The work on the first 18 months of the project provides a good basis for the further progress of the project delivery on mitigation targets based on observational evidence, Earth system model projections, and ecosystem analysis. We will also receive a better estimate of the robustness of the results on tipping elements, tipping point dynamics, and the issue of irreversibility.

COMFORT work has already contributed to a larger awareness of the scientific community and the public concerning potential damage from imminent ocean tipping points due to warming, ocean acidification, and deoxygenation. An example is the PNAS Perspective article that has been published to this extent. The wider societal implications of COMFORT results are that anticipation of abrupt and partially irreversible change of the oceans is put on improved measurable quantitative ground. The new results on emergent Earth system hazards will help to make efforts towards limiting the damage of increased greenhouse gas emissions to the marine part of the Earth system more effective and will contribute to a follow-up of the Paris agreement guided by scientific guardrails
COMFORT project structure