Nissen, C., Timmermann, R., Hoppema, M., Gürses, Ö., & Hauck, J. (2022). Abruptly attenuated carbon sequestration with Weddell Sea dense waters by 2100. Nature Communications, 13(1), 3402. https://doi.org/10.1038/s41467-022-30671-3
Antarctic Bottom Water formation, such as in the Weddell Sea in the Southern Ocean, is an efficient vector for carbon sequestration on time scales of centuries. Possible changes in carbon sequestration under changing environmental conditions are unquantified to date, mainly due to difficulties in simulating the relevant processes on high-latitude continental shelves. The authors of this study use a model setup including both ice-shelf cavities and oceanic carbon cycling and demonstrate that by 2100, deep-ocean carbon accumulation in the southern Weddell Sea is abruptly attenuated to only 40% of the 1990s rate in a high-emission scenario, while the rate in the 2050s and 2080s is still 2.5-fold and 4-fold higher, respectively, than in the 1990s. Assessing deep-ocean carbon budgets and water mass transformations, this decline was attributed to an increased presence of modified Warm Deep Water on the southern Weddell Sea continental shelf, a 16% reduction in sea-ice formation, and a 79% increase in ice-shelf basal melt. Altogether, these changes lower the density and volume of newly formed bottom waters and reduce the associated carbon transport to the abyss.
Policy relevant message:
Under the high emissions scenario, carbon sequestration by Weddell Sea dense water formation will reduce by 2100.
Three EU-funded projects under the Horizon 2020 programme, Tipping Points in the Earth System (TiPES), Our Common Future Ocean in the Earth System (COMFORT), and Tipping Points in Antarctic Climate Components (TiPACCs) have worked together towards developing a policy brief that presents the key findings to date from these projects. On that basis, we jointly formulated persisting knowledge gaps as well as policy recommendations.
The projects are hosted by The University of Copenhagen, The University of Bergen and NORCE and involve Bjerknes Centre for Climate Research.
A special report focussing on tipping points in the IPCC context is urgently needed to synthesise existing knowledge across the different scientific communities and inform policy makers and the general public about the risks of crossing tipping points in response to anthropogenic climate change.
Urgent implementation of a drastic reduction of GHG emissions, which are the primary cause of global warming and ocean acidification, in order to avoid further stability loss of major Earth system tipping elements and long-lasting changes in ocean properties.
Reduction of deforestation rates in both tropical and boreal forests alongside efforts toward binding international agreements to limit land-use change to sustainable levels. A global satellite-based monitoring system should also be implemented to assess the health of terrestrial ecosystems. At the same time, large-scale ecosystem protection and reforestation will help reduce atmospheric greenhouse gas concentrations globally and reduce drought risk regionally.
Appropriate global resource management needs to be implemented to achieve GHG emission reductions in line with the Paris Agreement, and to avoid problematic path dependencies and lock-in situations. Human societies must engage in the transformation towards i) green energy production, ii) sustainable exploitation and food production both on land and in the ocean, and iii) climate-friendly land use and urban planning and development.
Climate-neutral transformations need to be achieved urgently: there is already progress underway, such as the notable European Union Green Deal, including the goal to become climate neutral by 2050 supported by the ‘Restore our Ocean and Waters by 2030’ Mission, as well as the European Climate Pact. However, it is critical that these processes are accelerated to prevent the cumulative and compounding negative societal and Earth system impact.
Download the policy brief summarising findings of all three tipping point projectshere.
Oziel, L., Schourup-Kristensen, V., Wekerle, C., & Hauck, J. (2022). The Pan-Arctic Continental Slope as an Intensifying Conveyer Belt for Nutrients in the Central Arctic Ocean (1985–2015). Global Biogeochemical Cycles, 36(6), e2021GB007268. https://doi.org/10.1029/2021GB007268
Microscopic algae called phytoplankton are the base of the trophic chain, sustaining the entire Arctic Ocean (AO) ecosystem. In the central parts of the AO, multi-year sea-ice used to limit transmission of light in the surface ocean and therefore control phytoplankton growth and primary productivity. However, the massive loss in sea-ice during the last 3 decades allowed more and more light to penetrate the water column, making nutrient availability the main bottom-up control of the AO productivity. A major part of the bio-available nutrients reaching the surface in the central AO are transported with ocean currents from the adjacent North Atlantic and Pacific and from deeper water masses. Using a biogeochemical model resolving processes at high spatial resolution, we were able to quantify the different transport pathways of nutrients with ocean currents and revealed that despite increasing supply along the anticlockwise flowing boundary current, the central AO is still running into more severe nutrient limitation.
Policy relevant message:
The continental slope contributes to the transport of nutrients in the ArcticOcean. Yet, despite an intensification of ocean dynamics, the Arctic Ocean is still shifting from a light-limited to a nutrient-limited system.
The European Climate Pact unites people around a common cause to build a sustainable Europe for us all and all the generations to come. The Climate Pact initiative was launched by the European Commission as part of the European Green Deal in support of the EU’s goal to be the first climate-neutral continent in the world by 2050.
The European Climate Pact Ambassadors are people passionate about climate action, eager to make an impact and prevent climate change through various activities in their networks and local communities. Recently, Dagmara has become the European Climate Pact Ambassador representing COMFORT, the University of Bergen and Norway. Dagmara’s overarching goal is to directly translate Ocean and climate change scientific knowledge into political and societal action through two-way communication with policy makers and citizens. Oceans produce 50% of our oxygen, regulate weather and climate, and thus protecting it is a matter of global urgency. As a Climate Ambassador, her mission is to enhance the awareness of the Ocean’s role in climate regulation, the impacts of climate change on the Ocean and sustainable solutions to protect it.
There is a threat of imminent abrupt and irreversible transitions in the Earth system, both on land and in the ocean. A reduction in greenhouse gas (GHG) emissions and in land-use change must be implemented urgently to mitigate these changes through political, economic, and societal measures. Yet, considerable knowledge gaps remain concerning the processes underlying the dynamics of tipping elements,
Three EU funded Horizon2020 projects have been investigating tipping behaviour in the Earth system: Tipping Points in the Earth System (TiPES), Our Common Future Ocean in the Earth System (COMFORT), and Tipping Points in Antarctic Climate Components (TiPACCs). In the joint policy brief, you can find key findings of the three projects, persisting knowledge gaps as well as policy recommendations.
The policy brief is available for free download here.
We are pleased to share that COMFORT has been a top-ranking contributor to the latest IPCC report (Working Group II: Impacts, Adaptation and Vulnerability) among the European Climate, Infrastructure and Environment Executive Agency (CINEA)
Żebrowski, P., Dieckmann, U., Brännström, Å., Franklin, O., & Rovenskaya, E. (2022). Sharing the Burdens of Climate Mitigation and Adaptation: Incorporating Fairness Perspectives into Policy Optimization Models. In Sustainability (Vol. 14, Issue 7). https://doi.org/10.3390/su140737372
Mitigation of, and adaptation to, climate change can be addressed only through the collective action of multiple agents. The engagement of involved agents critically depends on their perception that the burdens and benefits of collective action are distributed fairly. Integrated Assessment Models (IAMs), which inform climate policies, focus on the minimization of costs and the maximization of overall utility, but they rarely pay sufficient attention to how costs and benefits are distributed among agents. Consequently, some agents may perceive the resultant model-based policy recommendations as unfair. In this paper, the authors propose how to adjust the objectives optimized within IAMs so as to derive policy recommendations that can plausibly be presented to agents as fair. They review approaches to aggregating the utilities of multiple agents into fairness-relevant social rankings of outcomes, analyze features of these rankings, and associate with them collections of properties that a model’s objective function must have to operationalize each of these rankings within the model. Moreover, for each considered ranking, the authors propose a selection of specific objective functions that can conveniently be used for generating this ranking in a model. Maximizing these objective functions within existing IAMs allows exploring and identifying climate polices to which multiple agents may be willing to commit.
Schwinger, J., Asaadi, A., Goris, N., & Lee, H. (2022). Possibility for strong northern hemisphere high-latitude cooling under negative emissions. Nature Communications, 13(1), 1095. https://doi.org/10.1038/s41467-022-28573-5
It is well established that a collapse or strong reduction of the Atlantic meridional overturning circulation (AMOC) would substantially cool the northern high latitudes. In this study the authors show that there is a possibility that such cooling could be amplified under deliberate CO2 removal and result in a temporary undershoot of a targeted temperature level. This behaviour was found in Earth system models that show a strong AMOC decline in response to anthropogenic forcing. Idealised simulations of CO2 removal with one of these models indicate that the timing of negative emissions relative to AMOC decline and recovery is key in setting the strength of the temporary cooling. This study shows that the pronounced temperature-fluctuations at high northern latitudes found in these simulations would entail considerable consequences for sea-ice and permafrost extent as well as for high latitude ecosystems.
Policy relevant message:
Cooling of the northern hemisphere as a result of a collapse or strong reduction of the Atlantic meridional overturning circulation (AMOC) can be amplified by Carbon dioxide removal (CDR) techniques. Therefore, not emitting CO2 into the atmosphere is a preferable action over post emission CO2 removal.
Norberg, J., Blenckner, T., Cornell, S. E., Petchey, O. L., & Hillebrand, H. (2022). Failures to disagree are essential for environmental science to effectively influence policy development. Ecology Letters, 00, 1–19. https://doi.org/10.1111/ele.13984
While environmental science, and ecology in particular, is working to provide better understanding to base sustainable decisions on, the way scientific understanding is developed can at times be detrimental to this cause. Locked-in debates are often unnecessarily polarised and can compromise any common goals of the opposing camps. The present paper is inspired by a resolved debate from an unrelated field of psychology where Nobel laureate David Kahneman and Garry Klein turned what seemed to be a locked-in debate into a constructive process for their fields. The present paper is also motivated by previous discourses regarding the role of thresholds in natural systems for management and governance, but its scope of analysis targets the scientific process within complex social-ecological systems in general. The authors of this paper identified four features of environmental science that appear to predispose for locked-in debates: (1) The strongly context-dependent behaviour of ecological systems. (2) The dominant role of single hypothesis testing. (3) High prominence is given to theory demonstration compared to an investigation. (4) The effect of urgent demands to inform and steer policy. This fertile ground is further cultivated by human psychological aspects as well as the structure of funding and publication systems.
Völker, C., & Ye, Y. (2022). Feedbacks Between Ocean Productivity and Organic Iron Complexation in Reaction to Changes in Ocean Iron Supply. Frontiers in Marine Science, 9. https://doi.org/10.3389/fmars.2022.777334
Low concentrations of iron, an important micronutrient for photosynthetic organisms, limit growth in large parts of the ocean. The solubility and availability of iron are to a large degree determined by organic iron-binding molecules, so-called ligands. While ligands come from a variety of sources, many of them are produced in autotrophic (nutrition produced by organisms themselves) or heterotrophic (nutrition gained externally) production in the ocean, leading to the possibility of feedbacks between marine primary production and iron availability. The diversity of ligands, reaching from siderophores, small molecules involved in bacterial iron uptake, to breakdown products and long-lived macromolecules like humic substances, means that feedbacks could be both negative and positive or there may even be no feedback at all. The authors of this study investigate first, how the cycling of this ligand pool can be described simplistically in a model such that it reproduces the observed global distribution of dissolved iron and phosphorus as closely as possible. They show that the inclusion of a ligand similar to refractory dissolved organic carbon leads to an improved agreement with observations in our model. The inclusion of a second, shorter-lived siderophore-like ligand does not strongly affect this agreement. In a second step, the authors study how feedbacks affect how iron distribution and oceanic productivity react to changes in external supply of iron. To be consistent with present-day iron distribution, the dominant feedback is positive, increasing the sensitivity of global biological productivity and hence carbon cycling to changes in iron supply. The strength of the feedback increases with increasing ligand life-time. The negative feedback associated with siderophore-like ligands has the potential to mitigate the positive feedback, especially at the surface and for global export production, but more research on the production and decay of siderophores is needed for a better quantification. Ocean biogeochemical models that assume a constant ligand concentration and hence neglect possible feedbacks may therefore underestimate the reaction of the global carbon cycle to the strong increase in dust deposition under future or glacial climate conditions.
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