The shift to data-driven urban climate governance alters accountability. This Review examines critically the drivers of the shift—standardization, transparency and capacity building—and how best to achieve equitable climate mitigation outcomes within this context.

Cities around the world are at the forefront of enacting climate mitigation policies, but effective action requires a better understanding of potential solutions. This Review offers a systematic exploration of the urban case study literature and discusses ways to best make use of the growing body of cases.

Cities have an important role in climate mitigation. Textual analysis techniques and regression modelling show the progress made by over 1,000 cities reporting in the European Covenant of Mayors initiative, active in climate action at the urban level.

Urban expansion and climate change interact to produce less night-time warming than their sum. Combined implementation of adaptation strategies can offset projected daytime urban warming when applied with GHG emissions reductions, but cannot offset projected nocturnal warming.

Growth in CO₂ emissions has slowed since the Paris Agreement 5 years ago. The COVID-19 pandemic has caused a drop in emissions of about 7% in 2020 relative to 2019, but strong policy is needed to address underlying drivers and to sustain a decline in global emissions beyond the current crisis.

Analysis of 1,550 future energy scenarios finds that uncertainty in solar photovoltaic (PV) uptake is mainly driven by institutional differences in designing and modelling these scenarios, rather than PV cost assumptions. This suggests more organizational diversity is needed in IPCC scenario design.

Warming causes mountain snowpack to melt earlier during local spring. An idealized model suggests that melt date sensitivity to warming depends largely on mean temperature and its seasonal cycle; the largest sensitivities are seen in coastal regions, the Arctic, western United States, Central Europe and South America.

The authors examine the effect of long-term experimental warming on the complexity and stability of molecular ecological networks in grassland soil microbial communities. They find warming increases network complexity, which is strongly correlated with network stability.

The response of low clouds to warming is uncertain among climate models and dominates spread in their projections. Satellite estimates of tropical cumulus and stratocumulus cloud feedbacks, derived using surface warming trends, suggest a more moderate climate sensitivity than many models predict.

The societal response to the pandemic has reduced global power demand, disproportionally affecting coal power generation and thus leading to a strong CO₂ emissions decline. Policy should apply 2020’s lessons to ensure that power sector emissions have peaked in 2018 and go into structural decline.

About 12 months into the COVID-19 pandemic, its immediate and lasting impacts on the climate system and fossil fuel economy are now better understood. These insights will be fundamental to the global recovery — and ideally the green transitions that accompany it — but the implementation will be hard-won.

Energy systems scenarios project a wide range of uncertainty in solar photovoltaic capacity, often thought to stem from techno-economic assumptions. Now research shows that the underlying sources of this uncertainty might be different than expected.

The 2009 pledge to mobilize US$100 billion a year by 2020 in climate finance to developing nations was not specific on what types of funding could count. Indeterminacy and questionable claims make it impossible to know if developed nations have delivered; as 2020 passes, opportunity exists to address these failures in a new pledge.

The ocean connects all corners of the Earth. It supports life, and we need to better understand and support it to ensure a prosperous future.