Jared Lewis’s research while affiliated with International Institute for Applied Systems Analysis and other places

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Publications (21)


Biases in ‘sustainable finance’ metrics could hinder lending to those that need it most
  • Article

October 2024

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20 Reads

Nature

Arjuna Dibley

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Alister Self

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[...]

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Ben Neville

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A food system transformation can enhance global health, environmental conditions and social inclusion
  • Preprint
  • File available

May 2023

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497 Reads

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4 Citations

The current global food system has detrimental outcomes for global health, environmental conditions and social inclusion. A coherent vision of a desirable food system can guide a sustainable food system transformation and help to structure political processes and private decisions by quantifying potential benefits, facilitating debates about co-benefits and trade-offs, and identifying key measures for desirable change. Such a transformation requires integrating measures targeting human diets, livelihoods, biosphere integrity, and agricultural management. Here, we apply a global food and land system modeling framework to quantify the impacts of 23 food system measures by 2050. Our multi-criteria assessment shows that a food system transformation can improve outcomes for health, the environment, social inclusion, and the economy. All individual measures come with trade-offs, particularly those targeting agricultural management, while few trade-offs and multiple co-benefits are linked to dietary change measures. By combining measures in packages, trade-offs can be reduced and co-benefits enhanced. We show that a sustainable food system also requires a transformation of the overall economy to stop global warming, reduce absolute poverty, and create alternative employment options. Within the context of a cross-sectoral sustainable development pathway, the food system transformation improves 14 of our 15 outcome indicators.

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The IPCC Sixth Assessment Report WGIII climate assessment of mitigation pathways: from emissions to global temperatures

December 2022

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359 Reads

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141 Citations

While the Intergovernmental Panel on Climate Change (IPCC) physical science reports usually assess a handful of future scenarios, the Working Group III contribution on climate mitigation to the IPCC's Sixth Assessment Report (AR6 WGIII) assesses hundreds to thousands of future emissions scenarios. A key task in WGIII is to assess the global mean temperature outcomes of these scenarios in a consistent manner, given the challenge that the emissions scenarios from different integrated assessment models (IAMs) come with different sectoral and gas-to-gas coverage and cannot all be assessed consistently by complex Earth system models. In this work, we describe the “climate-assessment” workflow and its methods, including infilling of missing emissions and emissions harmonisation as applied to 1202 mitigation scenarios in AR6 WGIII. We evaluate the global mean temperature projections and effective radiative forcing (ERF) characteristics of climate emulators FaIRv1.6.2 and MAGICCv7.5.3 and use the CICERO simple climate model (CICERO-SCM) for sensitivity analysis. We discuss the implied overshoot severity of the mitigation pathways using overshoot degree years and look at emissions and temperature characteristics of scenarios compatible with one possible interpretation of the Paris Agreement. We find that the lowest class of emissions scenarios that limit global warming to “1.5 ∘C (with a probability of greater than 50 %) with no or limited overshoot” includes 97 scenarios for MAGICCv7.5.3 and 203 for FaIRv1.6.2. For the MAGICCv7.5.3 results, “limited overshoot” typically implies exceedance of median temperature projections of up to about 0.1 ∘C for up to a few decades before returning to below 1.5 ∘C by or before the year 2100. For more than half of the scenarios in this category that comply with three criteria for being “Paris-compatible”, including net-zero or net-negative greenhouse gas (GHG) emissions, median temperatures decline by about 0.3–0.4 ∘C after peaking at 1.5–1.6 ∘C in 2035–2055. We compare the methods applied in AR6 with the methods used for SR1.5 and discuss their implications. This article also introduces a “climate-assessment” Python package which allows for fully reproducing the IPCC AR6 WGIII temperature assessment. This work provides a community tool for assessing the temperature outcomes of emissions pathways and provides a basis for further work such as extending the workflow to include downscaling of climate characteristics to a regional level and calculating impacts.



Schematic diagram of the assessment framework
The input scenario data refers to the institutional scenario data assessed in this study. The schematic is composed of database inputs (institutional scenario data, data from the scenarios underlying the IPCC’s Special Report on 1.5 °C), data processing steps, decision steps that lead to the application of certain steps, as well as user-defined inputs, and outputs of the framework.
Comparison of emission characteristics between the SR1.5 pathways and the institutional scenarios assessed in this study
a CO2 emissions from energy and industrial processes, (b) CO2 emissions from Agriculture, Forestry, and Land Use (AFOLU), (c) CH4 emissions, (d) N2O emissions. The box represents the interquartile range with the median represented by the solid horizontal line. The whiskers represent the full range across the corresponding pathway class. All emissions (apart from panel a) are infilled using the Quantile Rolling Windows (QRW) method, except for Shell Sky 1.5 which reports these emissions.
Assessment of the three criteria for Paris Agreement consistency
a, d Greenhouse gas emissions. b, e Temperature rise above 1850–1900 (the solid line is the ensemble median and the shaded plumes are the 33rd–66th percentile). c Probability of exceeding 1.5 °C. f Probability of exceeding 2 °C. Calculations for (b, c, e, f) are performed using MAGICC6.
Key energy system characteristics across pathways
The dashed vertical line separates two groups of indicators. Panels (a–d) are focused on the share of different fuels and/or technologies in total electricity generation. Panels (e, f) capture total final consumption, and the electrification of end-use. a Share of wind and solar in electricity generation. b Share of nuclear in electricity generation. c Share of coal in electricity generation. d Share of natural gas in electricity generation. e Share of electricity in total final consumption. f Total final energy consumption. The numbers in parentheses refer to the number of IPCC’s Special Report on 1.5 °C (SR1.5) database scenarios of each category. Where a specific scenario is missing in the panel (for instance, in panel e), it is either because the data are not reported, or, in the case of the International Energy Agency’s (IEA) Sustainable Development Scenario (SDS) from 2020, because the scenario ends in 2040.
Institutional decarbonization scenarios evaluated against the Paris Agreement 1.5 °C goal

August 2022

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203 Reads

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39 Citations

Scientifically rigorous guidance to policy makers on mitigation options for meeting the Paris Agreement long-term temperature goal requires an evaluation of long-term global-warming implications of greenhouse gas emissions pathways. Here we employ a uniform and transparent methodology to evaluate Paris Agreement compatibility of influential institutional emission scenarios from the grey literature, including those from Shell, BP, and the International Energy Agency. We compare a selection of these scenarios analysed with this methodology to the Integrated Assessment Model scenarios assessed by the Intergovernmental Panel on Climate Change. We harmonize emissions to a consistent base-year and account for all greenhouse gases and aerosol precursor emissions, ensuring a self-consistent comparison of climate variables. An evaluation of peak and end-of-century temperatures is made, with both being relevant to the Paris Agreement goal. Of the scenarios assessed, we find that only the IEA Net Zero 2050 scenario is aligned with the criteria for Paris Agreement consistency employed here. We investigate root causes for misalignment with these criteria based on the underlying energy system transformation.


The IPCC Sixth Assessment Report WGIII climate assessment of mitigation pathways: from emissions to global temperatures

June 2022

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272 Reads

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8 Citations

While the IPCC’s physical science report usually assesses a handful of future scenarios, the IPCC Sixth Assessment Working Group III report (AR6 WGIII) on climate mitigation assesses hundreds to thousands of future emissions scenarios. A key task is to assess the global-mean temperature outcomes of these scenarios in a consistent manner, given the challenge that the emission scenarios from different integrated assessment models come with different sectoral and gas-to-gas coverage and cannot all be assessed consistently by complex Earth System Models. In this work, we describe the “climate assessment” workflow and its methods, including infilling of missing emissions and emissions harmonisation as applied to 1,202 mitigation scenarios in AR6 WGIII. We evaluate the global-mean temperature projections and effective radiative forcing characteristics (ERF) of climate emulators FaIRv1.6.2, MAGICCv7.5.3, and CICERO-SCM, discuss overshoot severity of the mitigation pathways using overshoot degree years, and look at an interpretation of compatibility with the Paris Agreement. We find that the lowest class of emission scenarios that limit global warming to “1.5 °C (with a probability of greater than 50 %) with no or limited overshoot” includes 90 scenarios for MAGICCv7.5.3, and 196 for FaIRv1.6.2. For the MAGICCv7.5.3 results, “limited overshoot” typically implies exceedance of median temperature projections of up to about 0.1 °C for up to a few decades, before returning to below 1.5 °C by or before the year 2100. For more than half of the scenarios of this category that comply with three criteria for being “Paris-compatible”, including net-zero or net-negative greenhouse gas (GHG) emissions, are projected to see median temperatures decline by about 0.3–0.4 °C after peaking at 1.5–1.6 °C in 2035–2055. We compare the methods applied in AR6 with the methods used for SR1.5 and discuss the implications. This article also introduces a ‘climate-assessment’ Python package which allows for fully reproducing the IPCC AR6 WGIII temperature assessment. This work can be the start of a community tool for assessing the temperature outcomes related to emissions pathways, and potential further work extending the workflow from emissions to global climate by downscaling climate characteristics to a regional level and calculating impacts.


Multi-century dynamics of the climate and carbon cycle under both high and net negative emissions scenarios

May 2022

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439 Reads

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47 Citations

Future climate projections from Earth system models (ESMs) typically focus on the timescale of this century. We use a set of five ESMs and one Earth system model of intermediate complexity (EMIC) to explore the dynamics of the Earth's climate and carbon cycles under contrasting emissions trajectories beyond this century to the year 2300. The trajectories include a very-high-emissions, unmitigated fossil-fuel-driven scenario, as well as a mitigation scenario that diverges from the first scenario after 2040 and features an “overshoot”, followed by a decrease in atmospheric CO2 concentrations by means of large net negative CO2 emissions. In both scenarios and for all models considered here, the terrestrial system switches from being a net sink to either a neutral state or a net source of carbon, though for different reasons and centered in different geographic regions, depending on both the model and the scenario. The ocean carbon system remains a sink, albeit weakened by carbon cycle feedbacks, in all models under the high-emissions scenario and switches from sink to source in the overshoot scenario. The global mean temperature anomaly is generally proportional to cumulative carbon emissions, with a deviation from proportionality in the overshoot scenario that is governed by the zero emissions commitment. Additionally, 23rd century warming continues after the cessation of carbon emissions in several models in the high-emissions scenario and in one model in the overshoot scenario. While ocean carbon cycle responses qualitatively agree in both globally integrated and zonal mean dynamics in both scenarios, the land models qualitatively disagree in zonal mean dynamics, in the relative roles of vegetation and soil in driving C fluxes, in the response of the sink to CO2, and in the timing of the sink–source transition, particularly in the high-emissions scenario. The lack of agreement among land models on the mechanisms and geographic patterns of carbon cycle feedbacks, alongside the potential for lagged physical climate dynamics to cause warming long after CO2 concentrations have stabilized, points to the possibility of surprises in the climate system beyond the 21st century time horizon, even under relatively mitigated global warming scenarios, which should be taken into consideration when setting global climate policy.


Realization of Paris Agreement pledges may limit warming just below 2 °C

April 2022

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1,061 Reads

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437 Citations

Nature

Over the last five years prior to the Glasgow Climate Pact¹, 154 Parties have submitted new or updated 2030 mitigation goals in their nationally determined contributions and 76 have put forward longer-term pledges. Quantifications of the pledges before the 2021 United Nations Climate Change Conference (COP26) suggested a less than 50 per cent chance of keeping warming below 2 degrees Celsius2–5. Here we show that warming can be kept just below 2 degrees Celsius if all conditional and unconditional pledges are implemented in full and on time. Peak warming could be limited to 1.9–2.0 degrees Celsius (5%–95% range 1.4–2.8 °C) in the full implementation case—building on a probabilistic characterization of Earth system uncertainties in line with the Working Group I contribution to the Sixth Assessment Report⁶ of the Intergovernmental Panel on Climate Change (IPCC). We retrospectively project twenty-first-century warming to show how the aggregate level of ambition changed from 2015 to 2021. Our results rely on the extrapolation of time-limited targets beyond 2030 or 2050, characteristics of the IPCC 1.5 °C Special Report (SR1.5) scenario database⁷ and the full implementation of pledges. More pessimistic assumptions on these factors would lead to higher temperature projections. A second, independent emissions modelling framework projected peak warming of 1.8 degrees Celsius, supporting the finding that realized pledges could limit warming to just below 2 degrees Celsius. Limiting warming not only to ‘just below’ but to ‘well below’ 2 degrees Celsius or 1.5 degrees Celsius urgently requires policies and actions to bring about steep emission reductions this decade, aligned with mid-century global net-zero CO2 emissions.


Can updated climate pledges limit warming well below 2°C?

November 2021

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319 Reads

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119 Citations

Science

As part of the 2015 Paris Agreement, countries agreed to regularly revisit and enhance their national climate strategies and, every 5 years, to offer new emissions targets in the form of nationally determined contributions (NDCs) (1). This year’s 26th Conference of Parties provides a waypoint in this updating process as countries have been offering enhanced or completely new NDCs (2, 3) (henceforth, updated pledges) (4). We find that compared with the 2015 pledges, the updated pledges suggest a strengthening of ambition through 2030. By calculating probabilistic temperature outcomes over the 21st century for five emissions scenarios (see the figure and table S1), we find that the updated pledges provide a stronger near-term foundation to deliver on the long-term goals of the Paris Agreement of reducing the probability of the worst levels of temperature change this century and increasing the likelihood of limiting temperature change to well below 2°C.


Citations (16)


... Here, we examine potential pathways for the sustainable development of the Chinese food system. Our systematic approach aligns with a global sustainable food system development 15,16 to assess the combined health, environmental and socioeconomic dynamics under multiple future scenarios of the Chinese food system (Table 1). ...

Reference:

Bundled measures for China’s food system transformation reveal social and environmental co-benefits
A food system transformation can enhance global health, environmental conditions and social inclusion

... The use of NP as a SCM is a proven strategy to reduce CO₂ emissions associated with cement production [9,11]. Life Cycle Assessment (LCA) studies show that substituting 30-50 % of ordinary Portland cement with NP can lower the carbon footprint of concrete primarily due to a reduction in clinker production and lower energy required for grinding NP compared to clinker, the most emission-intensive component [19,51]. Local sourcing of NP further minimizes transportation-related emissions, enhancing its environmental benefits [52]. ...

The IPCC Sixth Assessment Report WGIII climate assessment of mitigation pathways: from emissions to global temperatures

... The International Energy Agency (IEA) has proposed a forecasting energy scenario or pathway called (Net Zero Emissions by 2050 Scenario) or (NZE Scenario) or simply (NZE), which predicts needed transitions in the global energy economy to reach net zero CO₂ emissions by 2050, which is consistent with limiting the global temperature rise in 2100 to 1.5 °C above the pre-industrial levels (with at least a 50% probability, and with limited overshoot) [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. In addition, the IEA-NZE scenario meets the 7 th Sustainable Development Goal (SDG-7), namely "Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all", which is aimed to be achieved by 2030 [65][66][67][68][69][70][71][72][73][74]. ...

Institutional decarbonization scenarios evaluated against the Paris Agreement 1.5 °C goal

... FaIR is an open-source, simple and computationally fast climate emulator of full-complexity ESMs. FaIR is one of the models used in the Intergovernmental Panel on Climate Change (IPCC) 6th Assessment Report (AR6) Working Group WGI and WGIII reports (IPCC, 2021;IPCC, 2022;Kikstra et al., 2022). The model consists of a simplified representation of the global carbon cycle coupled with a climate response model with two ocean layers (Millar et al., 2017;Smith et al., 2018). ...

The IPCC Sixth Assessment Report WGIII climate assessment of mitigation pathways: from emissions to global temperatures

... As opposed to earlier studies (Liddicoat et al., 2021;Koven et al., 2022), atmospheric CO 2 is freely evolving and not prescribed, whereas E FOS is prescribed and does not need to be diagnosed. From Eq. (6), we derive the cumulative airborne fraction (C AF ), ocean-borne fraction (C OF ), and land-borne fraction (C LF ): ...

Multi-century dynamics of the climate and carbon cycle under both high and net negative emissions scenarios

... Environmental impact assessments (EIAs) are another vital regulatory requirement, evaluating potential environmental effects of biofuel production, such as water consumption, soil degradation, and biodiversity impacts. Additionally, international frameworks like the Paris Agreement under the United Nations Framework Conservation on Climate Change underscore the importance of adhering to regularity standards for biofuel (Meinshausen et al. 2022). ...

Realization of Paris Agreement pledges may limit warming just below 2 °C

Nature

... GCAM solves for commodity prices in 5-year time steps such that supply and demand are in equilibrium in all energy, agriculture, and water markets. GCAM has been used for several decades in major studies assessing global climate mitigation policy progress 36 , alternative land protection policies 37 , and impacts of global trade 38 . ...

Can updated climate pledges limit warming well below 2°C?
  • Citing Article
  • November 2021

Science

... In general, seaweed farming is subject to globally increasing temperatures, more common and extreme heat waves, and an increase in ocean acidification (i.e., a decrease in pH), which implies a higher availability of CO 2 . By the end of this century, atmospheric CO 2 concentration is expected to achieve 1000 ppm (IPPC), which will cause an increment of 2.5-fold of the dissolved CO 2 concentrations and result in a decrease of approximately 0.4 pH units (Costa et al. 2021). In addition, surface water temperature is expected to increase by 0.5-5 °C during the next century (Düsedau et al. 2023). ...

Global Carbon and other Biogeochemical Cycles and Feedbacks

... Pathways belonging to the C1 category limit warming to 1.5°C in 2100 with a greater than 50% chance and hold warming below 1.5°C throughout the 21 st century with at least a 34% chance. This category of pathways have been used to identify pathways that are consistent with the Paris Agreement temperature goal 26,37 . We further proceed to classify these low and no overshoot pathways according to their consistency with an alternative, plausible interpretation of Article 2.1, and Article 4 of the Paris Agreement, that we lay out in this paper. ...

Institutional “Paris Agreement Compatible” Mitigation Scenarios Evaluated Against the Paris Agreement 1.5°C Goal

... They represent one of the largest terrestrial reservoirs of atmospheric carbon. Due to the forecasted climate change, ecosystems of the boreal biome may shift from a sink of atmospheric carbon (Winkler et al., 2021) to its source (Koven et al., 2021). Such an effect can be predicted due to CO 2 emissions from ecosystems being larger than CO 2 uptake during photosynthesis, which, in fact, signifies an increase in decomposition of organic matter and in root respiration (Ryu et al., 2019;Bonan, 2008). ...

23rd Century surprises: Long-term dynamics of the climate and carbon cycle under both high and net negative emissions scenarios