Using Integrated Assessment Models to Achieve the Paris Climate Target

Integrated assessment models (IAMs) have become central tools in global assessments of how to achieve the Paris climate target. But how reliable are the insights that can be drawn from IAMs? This thesis identifies and begins to assess three challenges associated with the use of IAM ensembles and individual IAMs to draw insights on climate mitigation. First, it highlights the importance of model independence for the robustness of insights that can be drawn from IAM ensembles. It develops a method that uses model documentation to construct a model family tree and uses this method to identify likely model dependencies between IAMs in the IPCC’s 5th assessment report (AR5). The analysis shows that the 14 most influential IAMs in AR5 form three branches, the largest of which (including MERGE, MESSAGE, MERGE-ETL, REMIND, WITCH, and BET) is responsible for about half of the scenarios in AR5. The model documentation also indicates that an expanding set of policy questions has incentivised a continuous increase in the detail and scope of IAMs over time. The findings give reason to believe that the diversity of model choices and assumptions included in the AR5 IAM ensemble might be limited. Second, it argues, based on a debate on values in science in philosophy, that the exclusively positive estimates of the cost of mitigation in AR5 are problematic because they don’t capture the full range of cost estimates found in the literature and because the uncertainty of the cost of mitigation is important. A review of the literature reveals that general equilibrium models, which are responsible for all the cost estimates in AR5, can (despite claims to the contrary) be modified to generate net negative costs, but that few of the IAMs in AR5 include mechanisms that typically contribute to net negative costs. It is also found that the model intercomparison studies that are responsible for most of the AR5 cost estimates focused only on aspects that increase the cost of mitigation. Overall, this gives reason to believe that the AR5 IAM ensemble might be biased against net negative mitigation costs. Third, it shows that predictions of climate policy impacts based on the Future Technology Transformations (FTT) simulation model are highly sensitive to a scaling parameter whose correct value is deeply uncertain. This result, which is obtained using Monte Carlo analysis and uniform and independent distributions (around ±50% of default values) for investor discount rates, technology build times, technology lifetimes, learning rates, and the scaling factor in a global sensitivity analysis, shows that the use of diffusion theory to derive technology deployment – which is seen by those who designed FTT to present a unique feature of the model – does not in itself ensure reliable predictions. In fact, the result indicates that predictions from both energy system optimisation models, which are more widely used, and FTT depend on similar unknowns related to future rates of technological change. Based on these three challenges, the thesis concludes, a diversity of model choices and assumptions is crucial for ensuring robust insights and for reflecting important uncertainties associated with IAM research

Systems Innovation, Inertia and Pliability: A mathematical exploration with implications for climate change abatement

This paper develops a stylised mathematical interpretation of innovation and inertia in economic systems, characteristics which feature in economics literature traceable back at least to Schumpeter and other economic theorists of innovation, as well as economic historians. Such characteristics are particularly important in energy systems and their potential response to climate change, where it is important to distinguish operational/fuel substitution from investment because the latter necessarily embodies both inertia and innovation, in systems as well as technologies. We argue that integrated assessments of climate abatement need to focus on investment, including the associated characteristics of both learning and inertia, and derive in detail the mathematical basis for incorporating these factors through marginal investment cost curves. From this we also introduce the concept of �pliability� as an expression of the ratio between costs which are significant but transitional (including learning investments, infrastructure and overcoming inertia), as compared to the enduring costs implied by purely exogenous technology assumptions. We then incorporate these features in a global model of optimal climate mitigation and show that they can generate a very different profile and pattern of results from traditional �integrated assessment� models, pinpointing the key sensitivities. We conclude that alongside all the attention devoted to evaluating climate change impacts and technology scenarios, far more effort should be devoted to understanding the structural characteristics of how the global energy system may respond to climate change mitigation

Challenges in the harmonisation of global integrated assessment models: a comprehensive methodology to reduce model response heterogeneity

Harmonisation sets the ground to a solid inter-comparison of integrated assessment models. A clear and transparent harmonisation process promotes a consistent interpretation of the modelling outcomes divergences and, reducing the model variance, is instrumental to the use of integrated assessment models to support policy decision-making. Despite its crucial role for climate economic policies, the definition of a comprehensive harmonisation methodology for integrated assessment modelling remains an open challenge for the scientific community. This paper proposes a framework for a harmonisation methodology with the definition of indispensable steps and recommendations to overcome stumbling blocks in order to reduce the variance of the outcomes which depends on controllable modelling assumptions. The harmonisation approach of the PARIS REINFORCE project is presented here to layout such a framework. A decomposition analysis of the harmonisation process is shown through 6 integrated assessment models (GCAM, ICES-XPS, MUSE, E3ME, GEMINI-E3, and TIAM). Results prove the potentials of the proposed framework to reduce the model variance and present a powerful diagnostic tool to feedback on the quality of the harmonisation itself

Constructing public health policies in post crisis countries: lessons to learn from the associations between free-sugars consumption and diabetes, obesity and dental caries before, during and after sanctions in Iraq.

BACKGROUND: This article aims to provide evidence for an informed public health policy on free-sugar consumption in post-crisis countries. METHODS: Iraq was selected as a case study. A systematic search for published data on the prevalence/incidence of type-2 diabetes, overweight/obesity, dental caries and free-sugar consumption levels in Iraq was conducted using MEDLINE, the Iraqi Academic Scientific journals and relevant international organisations' websites. Comparable data before (1980-1990), during (1991-2002) and after (2003-2015) the United Nations sanctions (UNS) were included. RESULTS: Ten studies were included. Quality scores ranged between 3 and 7/8. Free-sugar consumption decreased dramatically during the UNS (from 50 to 16.3 kg/person/year) and started increasing afterwards (24.1 kg/person/year). Changes in type-2 diabetes, overweight/obesity and caries levels mirrored those of free-sugar consumption. Caries declined markedly during UNS and started increasing afterwards. Comparable data on diabetes and overweight/obesity were only available for the periods during and after the UNS. Both of these conditions started increasing with increased free-sugar consumption after lifting the UNS. CONCLUSIONS: There is a need to develop a public health policy in post-crisis countries to maintain the reduction in free-sugar consumption, and hence promote both general and dental health, by integrating the common risk factor approach into the social determinant framework

The impact of U.S. re‐engagement in climate on the Paris targets

The Paris Agreement seeks to combine international efforts to keep global temperature increase to well-below 2°C. Whilst current ambitions in many signatories are insufficient to achieve this goal, optimism prevailed in the second half of 2020. Not only did several major emitters announce net-zero mitigation targets around mid-century, but the new Biden Administration immediately announced the U.S.’s re-entry into Paris and a net-zero goal for 2050. U.S. federal re-engagement in climate action could have a considerable impact on its national greenhouse gas emissions pathway, by significantly augmenting existing state-level actions. Combined with U.S. re-entry in the Paris Agreement, this could also serve as a stimulus to enhance ambitions in other countries. A critical question then becomes what such U.S. re-engagement, through both national and international channels, would have on the global picture. This commentary explores precisely this question, by using an integrated assessment model to assess U.S. national emissions, global emissions, and end-of-century temperatures in five scenarios combining different climate ambition levels in both the U.S. and the rest of the world. Our analyses finds that ambitious climate leadership by the Biden Administration on top of enhanced climate commitments by other the major economies could potentially be the trigger for the world to fulfill the temperature goal of the Paris Agreement

A multi-model analysis of long-term emissions and warming implications of current mitigation efforts

Most of the integrated assessment modelling literature focuses on cost-effective pathways towards given temperature goals. Conversely, using seven diverse integrated assessment models, we project global energy CO2 emissions trajectories on the basis of near-term mitigation efforts and two assumptions on how these efforts continue post-2030. Despite finding a wide range of emissions by 2050, nearly all the scenarios have median warming of less than 3 °C in 2100. However, the most optimistic scenario is still insufficient to limit global warming to 2 °C. We furthermore highlight key modelling choices inherent to projecting where emissions are headed. First, emissions are more sensitive to the choice of integrated assessment model than to the assumed mitigation effort, highlighting the importance of heterogeneous model intercomparisons. Differences across models reflect diversity in baseline assumptions and impacts of near-term mitigation efforts. Second, the common practice of using economy-wide carbon prices to represent policy exaggerates carbon capture and storage use compared with explicitly modelling policies

Diagenesis of archaeological bone and tooth

An understanding of the structural complexity of mineralised tissues is fundamental for exploration into the field of diagenesis. Here we review aspects of current and past research on bone and tooth diagenesis using the most comprehensive collection of literature on diagenesis to date. Environmental factors such as soil pH, soil hydrology and ambient temperature, which influence the preservation of skeletal tissues are assessed, while the different diagenetic pathways such as microbial degradation, loss of organics, mineral changes, and DNA degradation are surveyed. Fluctuating water levels in and around the bone is the most harmful for preservation and lead to rapid skeletal destruction. Diagenetic mechanisms are found to work in conjunction with each other, altering the biogenic composition of skeletal material. This illustrates that researchers must examine multiple diagenetic pathways to fully understand the post-mortem interactions of archaeological skeletal material and the burial environment