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1. Governing for Transformative Change across the Biodiversity–Climate–Society Nexus

   https://doi.org/10.1093/biosci/biac031  

   Pascual, Unai ; McElwee, Pamela D ; Diamond, Sarah E ; Ngo, Hien T ; Bai, Xuemei ; Cheung, William W ; Lim, Michelle ; Steiner, Nadja ; Agard, John ; Donatti, Camila I ; et al ( June 2022 , BioScience)

   Abstract Transformative governance is key to addressing the global environmental crisis. We explore how transformative governance of complex biodiversity–climate–society interactions can be achieved, drawing on the first joint report between the Intergovernmental Panel on Climate Change and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services to reflect on the current opportunities, barriers, and challenges for transformative governance. We identify principles for transformative governance under a biodiversity–climate–society nexus frame using four case studies: forest ecosystems, marine ecosystems, urban environments, and the Arctic. The principles are focused on creating conditions to build multifunctional interventions, integration, and innovation across scales; coalitions of support; equitable approaches; and positive social tipping dynamics. We posit that building on such transformative governance principles is not only possible but essential to effectively keep climate change within the desired 1.5 degrees Celsius global mean temperature increase, halt the ongoing accelerated decline of global biodiversity, and promote human well-being. 

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2. A framework for ensemble modelling of climate change impacts on lakes worldwide: the ISIMIP Lake Sector

   https://doi.org/10.5194/gmd-15-4597-2022  

   Golub, Malgorzata ; Thiery, Wim ; Marcé, Rafael ; Pierson, Don ; Vanderkelen, Inne ; Mercado-Bettin, Daniel ; Woolway, R. Iestyn ; Grant, Luke ; Jennings, Eleanor ; Kraemer, Benjamin M. ; et al ( January 2022 , Geoscientific Model Development)

   Abstract. Empirical evidence demonstrates that lakes and reservoirs are warming acrossthe globe. Consequently, there is an increased need to project futurechanges in lake thermal structure and resulting changes in lakebiogeochemistry in order to plan for the likely impacts. Previous studies ofthe impacts of climate change on lakes have often relied on a single modelforced with limited scenario-driven projections of future climate for arelatively small number of lakes. As a result, our understanding of theeffects of climate change on lakes is fragmentary, based on scatteredstudies using different data sources and modelling protocols, and mainlyfocused on individual lakes or lake regions. This has precludedidentification of the main impacts of climate change on lakes at global andregional scales and has likely contributed to the lack of lake water qualityconsiderations in policy-relevant documents, such as the Assessment Reportsof the Intergovernmental Panel on Climate Change (IPCC). Here, we describe asimulation protocol developed by the Lake Sector of the Inter-SectoralImpact Model Intercomparison Project (ISIMIP) for simulating climate changeimpacts on lakes using an ensemble of lake models and climate changescenarios for ISIMIP phases 2 and 3. The protocol prescribes lakesimulations driven by climate forcing from gridded observations anddifferent Earth system models under various representative greenhouse gasconcentration pathways (RCPs), all consistently bias-corrected on a0.5∘ × 0.5∘ global grid. In ISIMIP phase 2, 11 lakemodels were forced with these data to project the thermal structure of 62well-studied lakes where data were available for calibration underhistorical conditions, and using uncalibrated models for 17 500 lakesdefined for all global grid cells containing lakes. In ISIMIP phase 3, thisapproach was expanded to consider more lakes, more models, and moreprocesses. The ISIMIP Lake Sector is the largest international effort toproject future water temperature, thermal structure, and ice phenology oflakes at local and global scales and paves the way for future simulations ofthe impacts of climate change on water quality and biogeochemistry in lakes. 

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3. Atmospheric verification of emissions reductions on paths to deep decarbonization

   https://doi.org/10.1088/1748-9326/acbf69  

   Abdulla, Ahmed ; Telschow, Fabian JE ; Dohner, Julia ; Keeling, Ralph F. ; Schwartzman, Armin ; Victor, David G. ( March 2023 , Environmental Research Letters)

   A central challenge for sustaining international cooperation to cut global greenhouse gas emissions is confidence that national policy efforts are leading to a meaningful impact on the climate. Here, we apply a detection protocol to determine when the measurable signal of atmospheric CO₂can be distinguished from the noise of the carbon cycle and uncertainties in emission trends. We test that protocol with a database of 226 emission mitigation scenarios—the universe of scenarios vetted by the Intergovernmental Panel on Climate Change. These scenarios are descriptive of ‘baseline’ trajectories of emissions trends in the absence of new policies along with trajectories that reflect substantial policy efforts to stop warming at 1.5 °C–2 °C above pre-industrial levels, as embodied in the Paris Agreement. The most aggressive mitigation scenarios (i.e. 1.5 °C) require 11–16 years to detect a signal of demonstrable progress from the noise; 2 °C scenarios lengthen detection by at least a decade. As more climate policy analysts face the reality that goals of 1.5 °C–2 °C seem infeasible, they have developed ‘overshoot’ scenarios with emissions that rise above the agreed goal and then, later on, fall aggressively to achieve it. These pathways come at the political cost of a 1–2 decade delay in detection, even for the 1.5 °C scenarios. The Paris Agreement requires a global ‘stocktake’ that interrogates national mitigation efforts; our results suggest that this effort must grapple with the question of when the world can gain confidence that the diplomacy on climate is demonstrably making an impact.

    

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4. Heat stored in the Earth system 1960–2020: where does the energy go?

   https://doi.org/10.5194/essd-15-1675-2023  

   von Schuckmann, Karina ; Minière, Audrey ; Gues, Flora ; Cuesta-Valero, Francisco José ; Kirchengast, Gottfried ; Adusumilli, Susheel ; Straneo, Fiammetta ; Ablain, Michaël ; Allan, Richard P. ; Barker, Paul M. ; et al ( January 2023 , Earth System Science Data)

   Abstract. The Earth climate system is out of energy balance, and heat hasaccumulated continuously over the past decades, warming the ocean, the land,the cryosphere, and the atmosphere. According to the Sixth Assessment Reportby Working Group I of the Intergovernmental Panel on Climate Change,this planetary warming over multiple decades is human-driven and results inunprecedented and committed changes to the Earth system, with adverseimpacts for ecosystems and human systems. The Earth heat inventory providesa measure of the Earth energy imbalance (EEI) and allows for quantifyinghow much heat has accumulated in the Earth system, as well as where the heat isstored. Here we show that the Earth system has continued to accumulateheat, with 381±61 ZJ accumulated from 1971 to 2020. This is equivalent to aheating rate (i.e., the EEI) of 0.48±0.1 W m−2. The majority,about 89 %, of this heat is stored in the ocean, followed by about 6 %on land, 1 % in the atmosphere, and about 4 % available for meltingthe cryosphere. Over the most recent period (2006–2020), the EEI amounts to0.76±0.2 W m−2. The Earth energy imbalance is the mostfundamental global climate indicator that the scientific community and thepublic can use as the measure of how well the world is doing in the task ofbringing anthropogenic climate change under control. Moreover, thisindicator is highly complementary to other established ones like global meansurface temperature as it represents a robust measure of the rate of climatechange and its future commitment. We call for an implementation of theEarth energy imbalance into the Paris Agreement's Global Stocktake based onbest available science. The Earth heat inventory in this study, updated fromvon Schuckmann et al. (2020), is underpinned by worldwide multidisciplinarycollaboration and demonstrates the critical importance of concertedinternational efforts for climate change monitoring and community-basedrecommendations and we also call for urgently needed actions for enablingcontinuity, archiving, rescuing, and calibrating efforts to assure improvedand long-term monitoring capacity of the global climate observing system. The data for the Earth heat inventory are publicly available, and more details are provided in Table 4. 

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5. Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle

   https://doi.org/10.1073/pnas.1921914117  

   Yang, Simon ; Chang, Bonnie X. ; Warner, Mark J. ; Weber, Thomas S. ; Bourbonnais, Annie M. ; Santoro, Alyson E. ; Kock, Annette ; Sonnerup, Rolf E. ; Bullister, John L. ; Wilson, Samuel T. ; et al ( May 2020 , Proceedings of the National Academy of Sciences)

   Assessment of the global budget of the greenhouse gas nitrous oxide (${\mathrm{N}}_2$O) is limited by poor knowledge of the oceanic${\mathrm{N}}_2$O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatological${\mathrm{N}}_2$O emissions from the ocean by training a supervised learning algorithm with over 158,000${\mathrm{N}}_2$O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots of${\mathrm{N}}_2$O flux and reveals a vigorous global seasonal cycle. We estimate an annual mean${\mathrm{N}}_2$O flux of 4.2 ± 1.0 Tg N$\cdot {\mathrm{y}}^{-1}$, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. This${\mathrm{N}}_2$O flux ranges from a low of 3.3 ± 1.3 Tg N$\cdot {\mathrm{y}}^{-1}$in the boreal spring to a high of 5.5 ± 2.0 Tg N$\cdot {\mathrm{y}}^{-1}$in the boreal summer. Much of the seasonal variations in global${\mathrm{N}}_2$O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the global${\mathrm{N}}_2$O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmospheric${\mathrm{N}}_2$O budget.

    

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