Articles in 2021

Extreme weather events such as heatwaves and droughts are likely to occur more often under climate change. Such events can have an indirect effect on countries through global agricultural markets and food prices; this impact is stronger for higher-income than lower-income countries.

The authors show increased negative extremes in gross primary productivity in northern midlatitude ecosystems, particularly over grasslands and croplands, attributed to impacts of warm droughts. This highlights the vulnerability of terrestrial carbon sinks and food security to increasing extreme events.

Current action is insufficient to meet both the Paris Agreement and the Sustainable Development Goals. Integrated model-based analysis shows that strong interventions across many dimensions, together with ambitious lifestyle change, are needed to enable real progress towards the UN Agenda 2030.

The tropical Pacific east–west temperature gradient intensified recently, but climate models do not reproduce this, and they also predict future weakening. This discrepancy is attributed to a competition between long-term weakening and transient strengthening from aerosols and ocean equatorial upwelling.

Changes in extreme heat are often calculated as anomalies above a reference climatology. A different definition—week-day heatwaves surpassing the current record by large margins—shows that their occurrence probabilities depend on warming rate, not level, and are higher than during recent decades.

Blue carbon ecosystems take up and store substantial amounts of carbon. This represents an important ecosystem service in the context of climate change, with coastal ecosystems contributing nearly US$200 bn yr⁻¹ to blue carbon wealth.

Shipping routes through the Canadian Arctic are examined under 1, 2 and 4 °C global warming across four vessel classes, including ice breakers, Arctic community resupply ships, and passenger and private vessels. All routes show longer shipping seasons and navigability as a result of sea ice loss.

Finance flows consistent with low-emission pathways and resilient development are central to the Paris Agreement, yet confusion remains about Article 2.1(c). Clarity is needed, particularly of its relationship with climate finance, to differentiate responsibility and enable suitable monitoring.

Legal cases to force governments to reduce emissions or to pursue compensation for climate change-related losses are increasing. The scientific evidence used in such cases is found to be lagging behind state-of-the-art climate science; using up-to-date methodologies could improve causation claims.

High-mountain Asia streamflow is strongly impacted by snow and glacier melt. A regional model, combined with observations and climate projections, shows snowmelt decreased during 1979–2019 and was more dominant than glacier melt, and projections suggest declines that vary by river basin.

High-tide flooding (HTF) is more likely with sea-level rise. Projections along the United States coastline, considering likely sea-level rise and tidal amplitude cycles, suggest increased HTF event clustering in time and rapid increases in annual HTF frequency as early as the mid-2030s.

It is commonly assumed that the climate response to CO₂ removals is equal in magnitude and opposite in sign to the response to CO₂ emissions. The response, however, is asymmetric, meaning that offsetting CO₂ emissions with equal removals could lead to a different climate than avoiding the emissions.

Tropical rainfall exhibits cyclic north–south migration tracking the warmer hemisphere, and climate warming will delay this seasonally over land. Climate models and gridded precipitation data suggest a delay of about 4 days since 1979 is now detectable over Northern Hemisphere land and the Sahel.

Global humidity increases with warming, but the United States Southwest has shown summer decreases since 1950, with the largest declines on hot days attributed to decreased soil moisture, not atmospheric moisture transport. Projections are uncertain due to model spread in precipitation trends.

The authors assess the productivity of conservation agriculture systems for eight major crops under current and future climate using a global-scale probabilistic machine-learning approach, revealing substantial differences in yield gain probabilities across crop type, management practice, climate zone and geography.

Climate change communication is more likely to persuade when the message and the messenger resonate with the audience’s values and identities. A campaign field experiment testing online messages tailored to US Republicans increased their climate change beliefs, risk perceptions and issue importance.

The climate impact of water-table drawdown in peatlands is unclear as carbon dioxide emissions increase and methane emissions decrease due to drying. This study shows decreasing water-table depth results in net greenhouse gas emissions from global peatlands, despite reducing methane emissions.

Exploring how biodiversity and climate change are interlinked, the authors show that limiting warming could maintain tree diversity, avoiding primary productivity loss. Countries with greater climate change economic costs benefit most: a potential triple win for climate, biodiversity and society.

Using measurements from 139 global lakes, the authors demonstrate how long-term thermal habitat change in lakes is exacerbated by species’ seasonal and depth-related constraints. They further reveal higher change in tropical lakes, and those with high biodiversity and endemism.

Understanding the temperature sensitivity of soil respiration is critical to determining soil carbon dynamics under climate change. Spatial heterogeneity in controls highlights the importance of interactions between vegetation, soil and climate in driving the response of respiration to warming.