key: cord-0924078-inag5qoa
authors: Strapasson, Alexandre; Woods, Jeremy; Pérez-Cirera, Vanessa; Elizondo, Alejandra; Cruz-Cano, Diego; Pestiaux, Julien; Cornet, Michel; Chaturvedi, Rajiv
title: Modelling carbon mitigation pathways by 2050: Insights from the Global Calculator
date: 2020-05-13
journal: nan
DOI: 10.1016/j.esr.2020.100494
sha: 519b6b04dd0cc9b4a7017ebc1dec0704445d98a1
doc_id: 924078
cord_uid: inag5qoa

Abstract The Global Calculator (GC) can be used to assess a wide range of climate change mitigation pathways. The GC is an accessible integrated model which calculates the cumulative emissions of a basket of the main greenhouse gases that result from a set of technological and lifestyle choices made at the global level and as defined by the user within a single system dynamics tool. Using the GC, we simulated ambitious scenarios against business as usual trends in order to stay below 2 °C and 1.5 °C of maximum temperature change by the end of this century and carried out a sensitivity analysis of the entire GC model option space. We show that the calculator is useful for making broad simulations for energy, carbon and land use dynamics, and demonstrate how combined and sustained mitigation efforts across different sectors are urgently needed to meet climate targets.

The Global Calculator 1 (GC) is a pioneering initiative aimed at informing the climate debate at the international level, 23 by providing a relatively simple and highly accessible systems tool for policy makers, business leaders, NGOs and econometric model or a profit-optimization model. Optimisation functionality is instead passed to the user who makes 88 combinations of choices and is immediately shown the impacts arising from that set of choices (a pathway). The 89 calculator also provides a novel approach to assess energy demand and supply dynamics. The user begins by defining 90 or setting levels of core 'activities' (e.g., the amount of protein-rich food eaten, the distance travelled, the level of 91 heating and cooling needed for residential and commercial buildings), and then choses (and setting) the food, transport 92 and building solutions that enable those activities (or services) to be provided. For example, once these choices are 93 made, the overall demand for food is calculated and defines the impacts on land resources given the set of 94 technological choices for the provision of the food as made by the end-user (or as default settings under a given pre-95 defined pathway). All the pathways available will be defined by the set of services (activities) demanded and the 96 associated products (fertilisers, cars, houses and windmills) needed to supply those services, which in turn, are 97 manufactured with associated demand for resources (fuels, minerals, biomass, etc.) calculated. All activities, services 98 and product provision use energy which needs to be produced, transported and stored. Finally, both energy demand 99 and supply use fuel resources. This enables the model to be used to assess the impact of both behavioural (e.g., eating 100 and heating habits, modal switching in transport) and technological changes (e.g., electric vehicles, renewable energy 101 (wind, PV, hydro and biomass) and product innovation). To become operational, the calculator deploys a number of representative levers, which are all interconnected as a 106 broad integrated system that may vary over time. A lever is an issue that may substantially affect greenhouse gas forth, by using interpolation between whole levels. Some few levels do not have this type of growing levels of carbon 114 mitigation effort; instead, they vary from levels A to D, given that this variation may not necessarily reduce or increase 115 emissions, comparatively to each other, this would depend on the broad scenario. For example, the GC has a lever 116 about bioenergy provision, which can be offered as either liquid or solid biofuels (note: biogas is a consequential 117 energy from anaerobic digestion) and, hence, the emissions would depend on how they are integrated in their 118 respective commodity chains across the other sectors of the calculator. Further explanations about the levers' levels of 119 all sectors and how they were calibrated can be found in the supporting documentation available on the GC website. A 120 brief explanation about the levers' calibration is also available on dedicated pagers, by clicking on the information 121 icon beside each lever on the calculator's web tool. The focus of this paper is to run some selected scenarios and a sensitivity analysis of the entire model, similarly to the 126 assessment carried out by Elizondo to exemplify the level of effort that would be required to hold the increase in Global temperature 'to well-below 2°C, 143 and pursuing efforts to limit it to 1.5°C' by 2100 , as stated in Article 2 of the Paris Agreement [8]. The temperature 144 change calculated is for the year 2100 and represents a 50% chance of keeping temperature below 2°C and 1.5°C, 145 respectively, based on the GHG abatement contributions and energy use by 2050, extrapolated to 2100. These 146 scenarios are compared with a Business-As-Usual (BAU) pathway, as described below. Further information on the 147 assumptions underpinning each of the lever levels is available from the GC web tool. distributed pathway was originally developed by the DECC et al. [5] , not to be confused with the 'IEA2DS' example 162 pathway that is also available in the GC. There is an increased ambition from both sides of energy markets, demand 163 and supply, when compared to the BAU case. In addition to energy, land is used with more efficient land use The third scenario is a new simulation that represents an even higher mitigation effort that is required to meet the In terms of demography, all three pathways assume that the global population will rise from the current 7.3 billion to In order to replicate these three proposed simulations (i.e., BAU, 1.5D and 2D) directly on the web tool, 197 Table 1 provides the levels of effort used here for simulating each of the three pathways according to the assessed 198 scenario. It is worth noting that the calculator is able to present a large number of mitigation pathways, resulting from 199 the combinatorics of all levers' levels (and intermediate levels) and, therefore, these three chosen scenarios were 200 selected to demonstrate the functionality of the calculator. There are a number of other example pathways available on 201 the web tool, including scenarios proposed by businesses and NGOs. In addition, the GC offers an approximate 202 representation of the IPCC Representative Concentration Pathways 5 (RCPs) for 2.6, 6.0 and 8.5 W/m 2 of radiative 203 forcing 6 in the year 2100 relative to pre-industrial levels, whilst these radiative forcing levels are derived from 204 different GHG concentration trajectories [7] . Although the representation of RCPs in the GC was not assessed in this 205 article, they are also available in the list of example pathways shown on the GC's web tool. 206 207 5 The IPCC Fifth Assessment Report (AR5) provides a number of Representative Concentration Pathways (RCPs) for assessing ranges of potential global warming scenarios. Each RCP represents an equivalent radiative forcing effect in the year 2100 relative to pre-industrial levels, such as, +2.6, +4.5, +6.0, and +8.5 W/m 2 , globally. 6 The term radiative forcing has been used by the IPCC to represent a perturbation in the radiative energy balance of the Earth's climate system, for example, due to an increase in the concentration of greenhouse gases in the atmosphere. 

The sensitivity analysis was carried out by firstly setting the GC to its default IEA6DS pathway (our BAU pathway).

Then, each lever was individually set in-turn to its mitigation levels 1, 2, 3 and 4, with the changes to total greenhouse 212 emissions by 2050 at each level recorded. Each lever was tested one at a time, moving back to the default IEA6DS 213 example pathway after the changes were made to a lever's settings. Thus, it was possible to assess the potential impact 214 of each individual lever and its respective four levels of effort. This is important to reflect on the significance of each 

The results and discussion are split into three sub-sections: firstly, the modelling simulations, providing a comparative 221 analysis of the three assessed carbon mitigation pathways; secondly, the results from the sensitivity analysis; thirdly, 222 some additional considerations. Source: Prepared by the authors, using the Global Calculator.

The GC also provides a Sankey diagram for energy flows between supply and demand, as shown in Figure 5 , Figure 6 because it depends on the availability of surplus land before it can make a significant contribution to emissions 376 reductions, with surplus land only becoming available dependent on potential productivity improvements in cropping 377 and in energy crops, moderation in diets (as discussed above) and the use of agricultural residues, as discussed by 378 Strapasson et al. [2] also using the GC.

The sensitivity analysis may also vary according to the baseline considered for the assessment. Figure 12 shows, for 

It is important to clarify that the GC does not provide disaggregated results, for example, per continent or at country 405 level. This is because its model's dataset either uses consolidated information at global scale or estimated global 406 weighted averages using regional data e.g. in the case of assessing changes in transport modes (travel sector) and 

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The authors acknowledge the effort of the team responsible for preparing the GC as an open access tool, sponsored by 450 the former UK DECC (currently UK BEIS) and Climate-KIC, particularly the following colleagues and respective

• The Global Calculator is able to demonstrate carbon mitigation pathways for both 2 o C and 1.5 o C targets.• The model enables its users to design and reflect on new global energy strategies and policies.• The sensitivity analysis shows each sector's contribution for reducing GHG emissions globally.

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: