Volume 11 Issue 3, March 2021

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.

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.

Gender has a powerful influence on experiences of, and resilience to, climate change. In this Review, the authors provide an overview of four common gender assumptions, and offer four suggestions for a more informed pursuit of gender equality in climate change policy and practice.

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.

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.

Global emissions could decrease 3.9–5.6% over 5 years due to COVID-19, and the interconnected economy means lockdown-related declines reach beyond borders. As countries look to stimulate their economies, how fiscal incentives are allocated and invested will determine longer-term emission changes.

Quantifying the temperature impacts of anthropogenic emissions helps monitor proximity to the Paris Agreement goals. Human activities warmed global mean temperature during the past decade by 0.9 to 1.3 °C above 1850–1900 values, with 1.2 to 1.9 °C from greenhouse gases and −0.7 to −0.1 °C from aerosols.

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.

Tibetan Plateau runoff projections are uncertain due to precipitation change uncertainty in climate models. Historical precipitation–circulation relationships constrain future wet-season precipitation and runoff change, suggesting worsening water scarcity for the Indus and Ganges river basins.

Projections of terrestrial water storage (TWS)—the sum of all continental water—are key to water resource and drought estimates. A hydrological model ensemble predicts climate warming will more than double the land area and population exposed to extreme TWS drought by the late twenty-first century.

Forest management for climate mitigation plans requires accurate data on carbon fluxes to monitor policy impacts. Between 2001 and 2019, forests were a net sink of carbon globally, although emissions from disturbances highlight the need to reduce deforestation in tropical countries.

The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.

Warming is shifting temperate zones to become more tropical. Natural warming and CO₂ vent sites show that acidification buffers warming effects, reducing sea urchin numbers and grazing, thus creating a turf-dominated temperate habitat that is less hospitable to tropical fish than urchin barrens.

Ambitious policy instruments are needed to support the transition to low-carbon economies. This systematic review identifies what we know about positive and negative impacts of ten selected instruments on environmental, technological and socioeconomic outcomes, and how to minimize negative impacts.

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.