To achieve the temperature goal of the Paris Agreement, transformative actions are needed. The circular economy (CE) is one concept that gained popularity in recent years, with its proclaimed selling point to combine economic development with benefits to businesses, society, and the environment. However, definitions of CE diverge, applications appear across vastly different settings, and overall there is a lack of understanding of how much CE strategies can contribute to climate change mitigation (mitigation). We systematically screened 3244 records in Web of Science and Scopus, restricted to papers in English. We then selected studies against pre-determined eligibility criteria that, had to (1) refer explicitly to CE or closely related concepts (e.g. performance economy, cradle-to-cradle, material or product efficiency); and (2) refer to a climate change mitigation potential. We identified 341 studies, summarized, and grouped into six sectors (industry, waste, energy, buildings, transport, and agriculture). These sectors are not completely mutually exclusive, but partially overlapping. Nonetheless, sectoral classifications relate to existing categorizations and map well with international assessments of climate change mitigations, such as those of the Intergovernmental Panel on Climate Change (IPCC). Our review sets out to summarize the results of the scientific literature on the extent to which CE strategies can contribute to mitigation. Even though our query explicitly required a consideration of climate change, only 10% of all studies contributed insights on how the CE can support mitigation. We find that the highest saving potential is evidenced in the industry, energy, and transport sector; mid-range savings in the waste and building sector; and lowest gains are to be expected in agriculture. The majority of studies investigate incremental measures claiming but not demonstrating climate change mitigation. Most studies indicate potential but implementation remains weak. Assessments should move from attributional to consequential analysis to avoid misleading policy makers.

Urban transport provides access to multiple services, structures and impedes daily life of residents, and translates into wellbeing considerations, sustainability impacts, and GHG emissions. Thus motivated, multiple disciplines, ranging from psychology to urban planning, are invested in understanding the potential for transitioning to low-carbon and sustainable urban transport systems. While each discipline has carved out a growing body of knowledge, a consistent cross-disciplinary understanding of psychological, sociological, and urban form determinants of urban mobility choices is, perhaps surprisingly so, still lacking. Here, we systematically review the reviews of several strands of literature and lay out the evidence for individual, social, and infrastructure level factors pertinent to urban mode choice. Synthesizing the results from 75 review papers, we find that all three dimensions (individual, social, and infrastructure) unambiguously interfere with mode choice. Individuals are most motivated to shift modes, if they are well informed, if personal norms match low-carbon mode use, and, most importantly, if they perceive to have personal control over decisions. Perceptions about common travel behaviour (descriptive social norms), especially if supported by perceived normative beliefs of others (injunctive norms), are highly influential to support mode shift. However, the overall margin of shift as induced by individual and social settings remains limited. Instead, the infrastructure factors explain large differences in mode choice. New shared mobility modes, and teleworking and shopping, add a long tail to modes chosen, but are no game changer. We conclude that a transition to low-carbon mobility requires low-carbon infrastructure, which leverages enthusiastic individuals’ concerns and empowers them for mode change, and that address safety concerns prevalent especially in cities of the Global South. The mode shift to low-carbon option can then be sustained and enhanced by social influence in the form of collective social norms.

Despite the importance of evaluating all mitigation options so as to inform policy decisions addressing climate change, a systematic analysis of household-scale interventions to reduce carbon emissions is missing. Here, we address this gap through a state-of-the-art machine-learning assisted meta-analysis to comparatively assess the effectiveness of a range of monetary and behavioral interventions in energy demand of residential buildings. We identify 122 studies and extract 360 effect sizes representing trials on 1.2 million households in 25 countries. We find that all the studied interventions reduce energy consumption of households. Our meta-regression evidences that monetary incentives are on an average more effective than behavioral interventions, but deploying the right combinations of interventions together can increase overall effectiveness. We estimate global cumulative carbon emissions reduction of 8.64 Gt CO2 by 2040, though deploying the most effective packages and interventions could result in greater reduction. While modest, this potential should be viewed in conjunction with the need for derisking mitigation with energy demand reductions and realizing substantial co-benefits.

Urban street space is increasingly contested. However, it is unclear what a fair street space allocation would look like. We develop a framework of ten ethical principles and three normative perspectives on street space -streets for transport, streets for sustainability, and streets as place -and discuss 14 derived street space allocation mechanisms. We contrast these ethically grounded allocation mechanisms with real-world allocation in 18 streets in Berlin. We find that car users, on average, had 3.5 times more space available than non-car users. While some allocation mechanisms are more plausible than others, none is without normative implications. Without exception, all principles suggest that on-street parking for cars is difficult to justify, and that more space should be allocated to cycling. We argue that street space fairness principles should be systematically integrated into urban and transport planning.

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