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The Paris Agreement on climate change aims to improve cooperation by allowing governments to set their own commitments. Its success hinges on whether governments and investors believe those national commitments. To assess credibility, we interrogate a large novel sample of climate policy elites with decades of experience and well-placed to evaluate whether nations’ policy pledges are aligned with what they are politically and administratively able to implement. This expert assessment reveals that countries making the boldest pledges are also making the most credible pledges, contrasting theoretical warnings of a trade-off between ambition and credibility. We find that the quality of national political institutions is the largest explanator of the variation in credibility, and Europe’s credibility is exceptionally high. We also find that economic factors, such as the costs and benefits of controlling emissions, are statistically unimportant in explaining the credibility of national pledges to cooperate.

Traditionally, analysis of the costs of cutting greenhouse gas emissions has assumed that governments would implement idealized, optimal policies such as uniform economy-wide carbon taxes. Yet actual policies in the real world, especially in large federal governments, are often highly heterogeneous and vary in political support and administrative capabilities within a country. While the benefits of heterogeneous action have been discussed widely for experimentation and leadership, little is known about its costs. Focusing on the United States, we represent plausible variation (by more than a factor of 3) in the stringency of state-led climate policy in a process-based integrated assessment model (GCAM-USA). For a wide array of national decarbonization targets, we find that the nationwide cost from heterogeneous subnational policies is only one-tenth higher than nationally uniform policies. Such results hinge on two critical technologies (advanced biofuels and electricity) for which inter-state trade ameliorates the economic efficiencies that might arise with heterogeneous action. The nationwide cost of cutting emissions can be affected by local policies. This study considers the differences across the US states, with integrated assessment model results showing that varying state policies only increases nationwide costs by about 10%.

Stopping climate change requires revolutionary transformations in industry and agriculture. Ahead of several major climate meetings this year, policymakers struggling to measure progress on climate change should focus less on global emissions, which will be slow to change, and more on technological advances in pioneering niches.

To predict how society and political systems might actually respond to warming, upgrade integrated assessment models. To predict how society and political systems might actually respond to warming, upgrade integrated assessment models.

Decarbonization will require deployment of low-carbon technologies, but analysts have struggled to quantify which ones could be deployed in practice—especially where technologies have faced public opposition. For nuclear power, some analysts have tried to solve this problem with caps on deployment or nuclear-free scenarios; however, social science research has not offered nuanced guidance about these caps. We deploy an experiment involving a large U.S. sample (N = 1226) to disentangle public opposition due to the dread of nuclear power from opposition stemming from its actuarial risk. Respondents are asked to build a power generation portfolio that cuts CO2 emissions, given information about the actuarial risks of technologies. Half the sample is exposed to the nuclear power label while the other half is treated with the risk information but blinded to the label. Respondents who see the labels deploy 6.6 percentage points less nuclear power as a share of the U.S. electricity mix. Our results suggest that dread about nuclear power leads respondents to choose 40% less nuclear generation in 2050 than they would have chosen in the absence of this dread. These methods could apply to other technologies, such as carbon storage, where there may be gaps between actuarial and perceived risks.

Using a multi-sector model of human and natural systems, we find that the nationwide cost from state-varying climate policy in the United States is only one-tenth higher than that of nationally uniform policy. The benefits of state-led action — leadership, experimentation and the practical reality that states implement policy more reliably than the federal government — do not necessarily come with a high economic cost.

In many jurisdictions, policy-makers are seeking to decentralize the electric power system while also promoting deep reductions in the emission of greenhouse gases (GHG). We examine the potential roles for residential energy storage (RES), a technology thought to be at the epicenter of these twin revolutions. We model the impact of grid-connected RES operation on electricity costs and GHG emissions for households in 16 of the largest U.S. utility service territories under 3 plausible operational modes. Regardless of operation mode, RES mostly increases emissions when users seek to minimize their electricity cost. When operated with the goal of minimizing emissions, RES can reduce average household emissions by 2.2-6.4%, implying a cost equivalent of $180 to $5160 per metric ton of carbon dioxide avoided. While RES is costly compared with many other emission-control measures, tariffs that internalize the social cost of carbon would reduce emissions by 0.1-5.9% relative to cost-minimizing operation. Policy-makers should be careful about assuming that decentralization will clean the electric power system, especially if it proceeds without carbon-mindful tariff reforms.

Global emissions of CO2 have been rising at 1–2% per year, and the gap between emissions and what is needed to stop warming at aspirational goals like 1.5ºC is growing. To stabilize warming at 1.5ºC, most studies find that societies must rapidly decarbonize their economy while also removing CO2 previously emitted to the atmosphere. In response to these realities, dozens of national governments, thousands of local administrative governments, and scores of scientists have made formal declarations of a climate crisis that demands a crisis response. In times of crisis, such as war or pandemics, many barriers to policy expenditure and implementation are eclipsed by the need to mobilize aggressively around new missions; and policymaking forged in crisis often reinforces incumbents such as industrial producers. Though highly motivated to slow the climate crisis, governments may struggle to impose costly polices on entrenched interest groups and incumbents, resulting in less mitigation and therefore a greater need for negative emissions.We model wartime-like crash deployment of CO2 direct air capture (DAC) as a policy response to the climate crisis, calculating (1) the crisis-level financial resources which could be made available for DAC; (2) deployment of DAC plants paired with all combinations of scalable energy supplies and the volumes of CO2 each combination could remove from the atmosphere; and (3) the effects of such a program on atmospheric CO2 concentration and global mean surface temperature.Government expenditure directed to crises has varied, but on average may be about 5% of national GDP. Thus, we calculate that an emergency DAC program with annual investment of 1.2–1.9% of global GDP (anchored on 5% of US GDP; $1–1.6 trillion) removes 2.2–2.3 GtCO2 yr–1 in 2050, 13–20 GtCO2 yr–1 in 2075, and 570–840 GtCO2 cumulatively over 2025–2100. Though comprising several thousand plants, the DAC program cannot substitute for conventional mitigation: compared to a future in which policy efforts to control emissions follow current trends (SSP2-4.5), DAC substantially hastens the onset of net-zero CO2 emissions (to 2085–2095) and peak warming (to 2090–2095); yet warming still reaches 2.4–2.5ºC in 2100. Only with substantial cuts to emissions (SSP1-2.6) does the DAC program hold temperature rise to 2ºC.Achieving such massive CO2 removals hinges on near-term investment to boost the future capacity for upscaling. With such prodigious funds, the constraints on DAC deployment in the 2–3 decades following the start of the program are not money but scalability. Early deployments are important because they help drive the technology down its learning curve (indeed, in the long run, initial costs matter less than performance ceilings); they are also important because they increase the potential for future rapid upscaling. Deployment of DAC need not wait for fully decarbonized power grids: we find DAC to be most cost-effective when paired with electricity sources already available today: hydropower and natural gas with renewables; fully renewable systems are more expensive because their low load factors do not allow efficient amortization of capital-intensive DAC plants.

Scholars and practitioners have focused in recent years on the potential for achieving cooperation in small “clubs” of countries. While solutions to global climate change will eventually re...

Under the Paris Agreement nations made pledges known as nationally determined contributions (NDCs), which indicate how national governments are evaluating climate risks and policy opportunities. We find that NDCs reveal important systematic patterns reflecting national interests and capabilities. Because the ocean plays critical roles in climate mitigation and adaptation, we created a quantitative marine focus factor (MFF) to evaluate how governments address marine issues. In contrast to the past, when oceans received minimal attention in climate negotiations, 70% of 161 NDCs we analysed include marine issues. The percentage of the population living in low-lying areas—vulnerable to rising seas—positively influences the MFF, but negotiating group (Annex 1 or small island developing states) is equally important, suggesting political motivations are crucial to NDC development. The analysis reveals gaps between scientific and government attention, including on ocean deoxygenation, which is barely mentioned. Governments display a keen interest in expanding marine research on climate priorities. The ocean is a key part of the climate system but is often neglected in individual country priorities. Analysis of Nationally Determined Contributions reveals 70% include marine issues. The level of inclusion varies dependent on country factors including vulnerability to rising seas.

Three trends will combine to hasten it, warn Yangyang Xu, Veerabhadran Ramanathan and David G. Victor. Three trends will combine to hasten it, warn Yangyang Xu, Veerabhadran Ramanathan and David G. Victor.

Deep decarbonization in the U.S. will require a shift to an electrified society dominated by low-carbon generation. Many studies assume a role for nuclear power in the new energy economy, and the nuclear industry anticipates an eventual transition from light water reactors to advanced, non-light water designs. The development of these advanced reactors is emblematic of the type of dramatic change that is needed to transition from fossil fuels and deeply decarbonize the energy system. The Office of Nuclear Energy (NE) in the U.S. is entrusted with the allocation of public sector expenditures for this transition, but there is little to show for its efforts; no advanced design is remotely ready for deployment. Here, we report results from structured interviews we conducted with 30 nuclear energy veterans to elicit their impressions of the state of U.S. fission innovation. Most experts assessed NE as having been largely unsuccessful in enabling the development of advanced designs. The interview results highlight the importance of leadership and programmatic discipline, and how their absence leads to poor performance in driving change. Responses point to the likely demise of nuclear power and nuclear science in the U.S. without significant improvements in leadership, focus and political support.

In 2015 China provided access to electricity to its entire population—the first of the large emerging and developing countries to achieve that landmark goal that most advanced industrialized countries met decades earlier. We found some key experiences and lessons to be learned from China’s successful program to provide electricity for all. Substantial funding from the central government, delivered by mechanisms sensitive to local provincial needs, were essential to success. Also vital was use of off-grid solar home systems for the most remote users for whom grid connection would be quite costly.

The Paris Agreement highlights the need for local climate leadership. The University Of California’s approach to deep decarbonization offers lessons in efficiency, alternative fuels and electrification. Bending the emissions curve globally requires efforts that blend academic insights with practical solutions.

This paper develops a new microgrid investment planning model that determines cost-optimal investment and operation of distributed energy resources (DERs) in a microgrid. We formulate the problem in a bilevel framework, using particle swarm optimization to determine investment and the DER-CAM model (Distributed Energy Resources Customer Adoption Model) to determine operation. The model further uses sequential Monte Carlo simulation to explicitly simulate power outages and integrates time-varying customer damage functions to calculate interruption costs from outages. The model treats nonlinearities in reliability evaluation directly, where existing linear models make critical simplifying assumptions. It combines investment, operating, and interruption costs together in a single objective function, thereby treating reliability endogenously and finding the cost-optimal trade-off between cost and reliability - two competing objectives. In benchmarking against a version of the DER-CAM model that treats reliability through a constraint on minimum investment, our new model improves estimates of reliability (the loss of load expectation) by up to 600%, of the total system cost by 6%-18%, of the investment cost by 32%-50%, and of the economic benefit of investing 27%-47%. Improvements stem from large differences in investment of up to 56% for natural gas generators, solar photovoltaics, and battery energy storage.

One of the most significant impacts of the United Nations Framework Convention on Climate Change (UNFCCC) has been the establishment of a participatory process for Reducing Emissions from Deforestation and Forest Degradation (REDD+). We analyse the case of Brazil, the country whose land-use emissions from deforestation and forest degradation have declined the most. Through semi-structured interviews with 29 country policy experts – analysed in full text around 7 categories of activities that existing literature identifies as central elements of an effective governance system – we find weak links between the international REDD+ system and what actually happens on the ground inside Brazil. The greatest weaknesses are rooted in the absence of any formal learning system, which prevents higher-level efforts from obtaining useful feedback from lower-level entities responsible for implementation. Analytically our approach is rooted in the idea of ‘experimentalist governance’ in which local policy experiments map the space of what is possible and effective with transformative land policy. These experiments provide information to broader international initiatives on how local implementation shapes the ability and strategy to reach global goals. The Brazilian experience suggests that even when international funding is substantial, local implementation remains a weak link. REDD+ reforms should focus less on the total amount of money being spent and much more on how those funds are used to generate useful local policy experiments and learning. Key policy insightsA nascent system of experimentalist governance to implement REDD+ is taking shape in Brazil. However, the potential for experimentalism to improve policy reforms within Brazil is far from realized;Experimentalist problem-solving approaches could have a big impact on REDD+ with stronger incentives to promote experimentation and learning from experience;Reforms to REDD+ incentive schemes should focus less on the total amount of money being spent and more on whether those funds are actually generating experimental learning and policy improvement – in Brazil and in other countries struggling with similar challenges. A nascent system of experimentalist governance to implement REDD+ is taking shape in Brazil. However, the potential for experimentalism to improve policy reforms within Brazil is far from realized; Experimentalist problem-solving approaches could have a big impact on REDD+ with stronger incentives to promote experimentation and learning from experience; Reforms to REDD+ incentive schemes should focus less on the total amount of money being spent and more on whether those funds are actually generating experimental learning and policy improvement – in Brazil and in other countries struggling with similar challenges.

Most studies of deep decarbonization find that a diverse portfolio of low-carbon energy technologies will be required, including carbon capture and storage (CCS) that mitigates emissions from fossil fuel power plants and industrial sources. While many projects essential to commercializing the technology have been proposed, most (>80%) end in failure. Here we analyze the full universe of CCS projects attempted in the U.S. that have sufficient documentation (N=39)—the largest sample ever studied systematically. We quantify 12 project attributes that the literature has identified as possible determinants of project outcome. In addition to costs and technological readiness, which prior research has emphasized, we develop metrics for attributes that are widely thought to be important yet have eluded systematic measurement, such as the credibility of project revenues and policy incentives, and the role of regulatory complexity and public opposition. We build three models—two statistical and one derived through the elicitation of expert judgment—to evaluate the relative influence of these 12 attributes in explaining project outcome. Across models, we find the credibility of revenues and incentives to be among the most important attributes, along with capital cost and technological readiness. We therefore develop and elicit experts’ judgment of 14 types of policy incentives that could alter these attributes and improve the prospects for investment in CCS. Knowing which attributes have been most responsible for past successes and failures allows developers to avoid past mistakes and identify clusters of near-term CCS projects that are more likely to succeed.