CMIP6 climate models imply high committed warming

Current climate change is highly transient, and Earth is at a significant distance from thermal equilibrium. This well-established finding is predominantly due to the large flux of thermal energy currently entering the oceans. If globally the sources and sinks of atmospheric GHGs were to become zero, this is identical to stating that their concentrations are subsequently invariant. Such a policy would correspond to a full offset of the remaining emissions by both land and ocean CO2 drawdown, as well as any implementation of carbon capture and storage (CCS) methods. The 5th Intergovernmental Panel on Climate Change (IPCC) report defines this as a “constant composition commitment

Decadal global temperature variability increases strongly with climate sensitivity

Climate-related risks are dependent not only on the warming trend from GHGs, but also on the variability about the trend. However, assessment of the impacts of climate change tends to focus on the ultimate level of global warming1, only occasionally on the rate of global warming, and rarely on variability about the trend. Here we show that models that are more sensitive to GHGs emissions (that is, higher equilibrium climate sensitivity (ECS)) also have higher temperature variability on timescales of several years to several decades2. Counter-intuitively, high-sensitivity climates, as well as having a higher chance of rapid decadal warming, are also more likely to have had historical ‘hiatus’ periods than lower-sensitivity climates. Cooling or hiatus decades over the historical period, which have been relatively uncommon, are more than twice as likely in a high-ECS world (ECS = 4.5 K) compared with a low-ECS world (ECS = 1.5 K). As ECS also affects the background warming rate under future scenarios with unmitigated anthropogenic forcing, the probability of a hyper-warming decade—over ten times the mean rate of global warming for the twentieth century—is even more sensitive to ECS

Testing the assumptions in emergent constraints: why does the “emergent constraint on equilibrium climate sensitivity from global temperature variability” work for CMIP5 and not CMIP6?

It has been shown that a theoretically derived relation between annual global mean temperature variability and climate sensitivity held in the CMIP5 climate model ensemble (Cox et al., 2018a, hereafter CHW18). This so-called emergent relationship was then used with observations to constrain the value of equilibrium climate sensitivity (ECS) to about 3 °C. Since this study was published, CMIP6, a newer ensemble of climate models has become available. Schlund et al. (2020) showed that many of the emergent constraints found in CMIP5 were much weaker in the newer ensemble, including that of CHW18. As the constraint in CHW18 was based on a relationship derived from reasonable physical principles, it is of interest to find out why it is weaker in CMIP6. Here, we look in detail at the assumptions made in deriving the emergent relationship in CHW18 and test them for CMIP5 and CMIP6 models. We show one assumption, that of low correlation and variation between ECS and the internal variability parameter, a parameter that captures chaotic internal variability and sub-annual (fast) feedbacks, that while true for CMIP5 is not true for CMIP6. When accounted for, an emergent relationship appears once again in both CMIP ensembles, implying the theoretical basis is still applicable while the original assumption in CHW18 is not. Unfortunately, however, we are unable to provide an emergent constraint in CMIP6 as observational estimates of the internal variability parameter are too uncertain

The momentum of the solar energy transition

Decarbonisation plans across the globe require zero-carbon energy sources to be widely deployed by 2050 or 2060. Solar energy is the most widely available energy resource on Earth, and its economic attractiveness is improving fast in a cycle of increasing investments. Here we use data-driven conditional technology and economic forecasting modelling to establish which zero carbon power sources could become dominant worldwide. We find that, due to technological trajectories set in motion by past policy, a global irreversible solar tipping point may have passed where solar energy gradually comes to dominate global electricity markets, without any further climate policies. Uncertainties arise, however, over grid stability in a renewables-dominated power system, the availability of sufficient finance in underdeveloped economies, the capacity of supply chains and political resistance from regions that lose employment. Policies resolving these barriers may be more effective than price instruments to accelerate the transition to clean energy

Deciding how to decide: Risk-opportunity analysis as a generalisation of cost-benefit analysis

Policymaking in the UK, the US and many other parts of the world relies heavily on cost-benefit analysis, applied within a market failure framework that rests on the theoretical foundation of welfare economics. These techniques have their roots in the so-called ‘Marginal Revolution’ of the 1870s. As the UK government’s guide to policy appraisal (the ‘Green Book’) acknowledges (section 5.5) these techniques are appropriate for informing policy in contexts of marginal change, but work less well outside those conditions. So, what should be done when the aim is to change big things quickly, or where opportunities for transformative change are available? Concerns have been raised that applying marginal analysis techniques outside their appropriate realm may create a bias towards inaction. But finance ministries may be equally concerned that if policymakers are given free rein to label their policies as ‘transformational’ in intent, and therefore exempt from cost-benefit analysis, a bias for action may be hard to contain. The challenge, then, is to define an approach to informing policy in a broad set of conditions that has analytical rigour, demands a proportionate amount of effort, and avoids undue bias in either direction

A solar future inevitable? How to shape policies to capture the opportunities of cheap solar

Solar power has already grown much faster globally than most governments and analysts expected. This looks set to continue: our model suggests solar is on track to dominate the global power sector even with no additional deployment subsidies. Its deployment will increase faster than is typically assumed, and we project costs including storage to continue falling. New coal and gas plants are set to become uneconomic earlier than anticipated, potentially costing twice as much as solar power with energy storage by the end of this decade. Grid upgrades and policies to support the deployment of energy storage will be important to taking full advantage of this opportunity

How are climate policies assessed in emerging economies? A study of ex-ante policy appraisal in Brazil, China, and India

Effective mitigation of climate change requires a robust set of policy interventions. Existing policy appraisal frameworks and approaches impact the design and choice of these policy options. However, their application to transformative climate policy can present several shortcomings. In light of criticism around current appraisal methods, we review the climate policy appraisal landscape and interview policy experts in three major emerging economies: Brazil, China and India. Little research has been done on the perception, approach, and practice of policy appraisal in these countries, even though they will have a significant impact on global progress to mitigate climate change. We find that policy appraisal in Brazil, China, and India is supported by guidelines, but the detail and implementation of those guidelines vary significantly. Cost–benefit analysis (CBA) is the prevailing decision-making framework in both Brazil and India whereas multi-criteria analysis is the dominant framework in China. Practitioners appear to understand CBA and its limitations well but also value its usability and the perception of robustness. Across all countries, political considerations can outweigh appraisal findings; respondents suggested this can be negative, in the sense that appraisal results are sometimes ignored, but can also be positive in the sense that other objectives are considered. Existing approaches present several limitations, particularly regarding transformational change, which could hamper progress to formulate and implement effective climate and energy policy

Energy transition in Brazil: innovation, opportunities and risks

This report summarises work performed during the past three years on innovation in the energy sector and the impact of environmental policies on trade and emissions, as part of an international programme on the Economics of Energy Innovation and System Transition (EEIST), with results from the programme in Brazil. It illustrates why (and how) the way in which policy is assessed matters for policymakers: specifically, tools that emphasise interactions between policies and an economy in constant evolution can pinpoint risks and opportunities. It draws on extensive knowledge as published in three main reports under the EEIST programme, which address (i) the theoretical underpinnings and implications for risk-opportunity analysis (ROA), from which follow (ii) ten principles for policymaking in the energy transition; and (iii) frames the modelling science around new economic modelling, with 15 case studies emerging from the interaction between modellers and policy engagement across Brazil, China and India. This report provides insights on how unique dimensions of the Brazilian landscape and financial situation give scope for effective action towards a low-carbon re-industrialisation. Written for technical and policy teams in Brazil, with particular relevance to the ministerial, development banks and energy regulators, it illustrates in particular that the dynamic nature of low-carbon re-industrialisation offers opportunity, with ROA a more useful tool than traditional (but impractical) cost-benefit analysis (CBA) to assess the green transition via empirical case studies. It supports this with four additional modelling case studies implementing the learning from this work in policy-relevant modelling. An appendix summarises the engagement strategy built upon communities of practice in Brazil, as a potential example to future science-policy interface collaboration.Este relatório resume o trabalho realizado durante os últimos três anos sobre a inovação no sector da energia e o impacto das políticas ambientais no comércio e nas emissões, como parte de um programa internacional sobre a Economia da Inovação Energética e da Transição de Sistemas (EEIST), com resultados do programa no Brasil. Ilustra por que (e como) a forma como a política é avaliada é importante para os decisores políticos: especificamente, as ferramentas que enfatizam as interações entre as políticas e uma economia em constante evolução podem identificar riscos e oportunidades. Baseia-se no amplo conhecimento publicado em três relatórios principais no âmbito do programa EEIST, que abordam (i) os fundamentos teóricos e as implicações para a análise de risco-oportunidade (ROA), dos quais se seguem (ii) dez princípios para a formulação de políticas na transição energética ; e (iii) enquadra a ciência da modelagem em torno de uma nova modelagem econômica, com 15 estudos de caso emergentes da interação entre modeladores e do envolvimento político no Brasil, China e Índia. Este relatório fornece insights sobre como dimensões únicas do cenário e da situação financeira brasileira dão espaço para ações eficazes em direção a uma reindustrialização de baixo carbono. Escrito para equipes técnicas e políticas no Brasil, com particular relevância para os ministérios, bancos de desenvolvimento e reguladores de energia, ilustra em particular que a natureza dinâmica da reindustrialização de baixo carbono oferece oportunidades, sendo o ROA uma ferramenta mais útil do que a tradicional (mas impraticável) análise custo-benefício (ACB) para avaliar a transição verde através de estudos de caso empíricos. Apoia isto com quatro estudos de caso de modelização adicionais que implementam a aprendizagem deste trabalho na modelização relevante para políticas. Um apêndice resume a estratégia de engajamento construída sobre comunidades de prática no Brasil, como um exemplo potencial para futura colaboração na interface ciência-política

Energy transition in Brazil: innovation, opportunities and risks

Brazil has recently re-committed to environmental policy and international cooperation. This enhances the practical value of joint research to accelerate a transition towards a more sustainable economy, in particular in view of its hosting of COP30, which will be held in the port city of Belem, on the Amazon river delta. This report summarises work performed during the past three years on innovation in the energy sector and the impact of environmental policies on trade and emissions, as part of an international programme on the Economics of Energy Innovation and System Transition (EEIST), with results from the programme in Brazil. It illustrates why (and how) the way in which policy is assessed matters for policymakers: specifically, tools that emphasise interactions between policies and an economy in constant evolution can pinpoint risks and opportunities. It draws on extensive knowledge as published in three main reports under the EEIST programme, which address (i) the theoretical underpinnings and implications for risk-opportunity analysis (ROA), from which follow (ii) ten principles for policymaking in the energy transition; and (iii) frames the modelling science around new economic modelling, with 15 case studies emerging from the interaction between modellers and policy engagement across Brazil, China and India. This report provides insights on how unique dimensions of the Brazilian landscape and financial situation give scope for effective action towards a low-carbon re-industrialisation. Written for technical and policy teams in Brazil, with particular relevance to the ministerial, development banks and energy regulators, it illustrates in particular that the dynamic nature of low-carbon re-industrialisation offers opportunity, with ROA a more useful tool than traditional (but impractical) cost-benefit analysis (CBA) to assess the green transition via empirical case studies. It supports this with four additional modelling case studies implementing the learning from this work in policy-relevant modelling. An appendix summarises the engagement strategy built upon communities of practice in Brazil, as a potential example to future science-policy interface collaboration