Humanity is putting unprecedented pressures on the Amazon forest system through global warming and land use changes. As the Amazon forest may undergo self-reinforcing transitions, these pressures could lead to system-wide changes across major parts of Amazonian ecosystems. Here we apply a dynamical systems model to assess the local and far-reaching cascading transition risks towards degraded ecosystems in the Amazon biome under different Shared Socioeconomic Pathways. For these emission scenarios, we constructed how moisture is transported through the atmosphere within the Amazon basin using an established atmospheric moisture-tracking model. Without accounting for deforestation, we find a critical global warming threshold of 3.7–4.0 °C, beyond which up to a third of the Amazon forest risks losing stability. However, when considering deforestation, we find a near system-wide transition of the Amazon forest (62−77% of the area) under the combination of a lower threshold range of global warming of 1.5–1.9 °C and deforestation of 22–28%. The large majority of the simulated transitions is caused by spatial knock-on effects from increasing drought intensities, leading to long-ranging and self-propelling cascades on scales of hundreds to thousands of kilometres. Overall, our results reinforce the need to keep global warming levels below 1.5 °C and halt deforestation, as well as ecologically restore degraded forests to avoid high transition risks across the Amazon forest system.

Mapping ecosystem integrity is a key task of the planetary-boundaries framework. Two new control variables have been suggested for the core planetary boundary for functional biosphere integrity: (1) human appropriation of net primary production (HANPP) and (2) a metric for ecological disruption (EcoRisk). However they have not yet been mapped spatially and temporally explicitly. Here, we use simulations with the dynamic global vegetation model LPJmL to map the status of these variables at a spatial resolution of 0.5° × 0.5° for every year since 1600. We additionally quantify local degradation thresholds by comparison with independent biosphere integrity indicators. We finally aggregate results globally to a planetary boundary status as the land area transgressing the local thresholds. We find that the local boundary is currently transgressed on 60% of the global land area, with 38% already at high risk of degradation. This study provides an important first step and opens the opportunity for further research, especially for finding a planetary-scale threshold.

Global environmental pressures from food systems threaten biodiversity and the stability of the Earth system, yet the safe operating space for food systems is unknown. Here we calculate food system boundaries as shares of planetary boundaries, proposing budgets for the food system across nine boundaries. Our results indicate that food systems are a critical driver of planetary boundary transgressions, dominating at least four transgressed boundaries (that is, biosphere integrity, land system change, freshwater change and biogeochemical flows) while strongly contributing to the transgression of two more (that is, climate change and novel entities). Moreover, global food systems are currently beyond all nine food system boundaries; moving to the safe operating space requires reducing related greenhouse gas emissions substantially, halting the conversion of intact nature to agriculture, redistributing fertilizer inputs, limiting pesticide and antibiotic use, and preserving critical freshwater flows without negatively affecting yields.

In light of uncertainties regarding climate sensitivity and future anthropogenic greenhouse gas emissions, we explore the plausibility of global warming over the next millennium which is significantly higher than what is usually expected. Although efforts to decarbonize the global economy have significantly shifted global anthropogenic emissions away from the most extreme emission scenarios, intermediate emission scenarios are still plausible. Significant warming in these scenarios cannot be ruled out as uncertainties in equilibrium climate sensitivity (ECS) remain very large. Until now, long-term climate change projections and their uncertainties for such scenarios have not been investigated using Earth system models (ESMs) that account for all major carbon cycle feedbacks. Using the fast ESM CLIMBER-X with interactive CO₂ and CH₄ (the latter typically not included in most models), we performed simulations for the next millennium under extended SSP1-2.6, SSP4-3.4 and SSP2-4.5 scenarios. These scenarios are usually associated with peak global warming levels of 1.5 ^∘C, 2 ^∘C and 3 ^∘C, respectively, for an ECS of ∼3 ^∘C, considered the best estimate in the latest Intergovernmental Panel on Climate Change (IPCC) report. As ECS values lower or higher than this estimate cannot be ruled out, we emulate a wide range of ECS from 2 ^∘C to 5 ^∘C, defined as the 'very likely' range by the IPCC. Our results show that achieving the Paris Agreement goal of a 2 ^∘C temperature increase is only feasible for low emission scenarios and if ECS is lower than 3.5 ^∘C. With an ECS of 5 ^∘C, peak warming in all considered scenarios more than doubles compared to an ECS of 3 ^∘C. Approximately 50% of this additional warming is attributed to positive climate–carbon cycle feedbacks with comparable contributions from CO₂ and CH₄. The interplay between potentially high ECS and carbon cycle feedbacks could drastically enhance future warming, demonstrating the importance of properly accounting for all major climate feedbacks and associated uncertainties in projecting future climate change.

Under current emission trajectories, temporarily overshooting the Paris global warming limit of 1.5 °C is a distinct possibility. Permanently exceeding this limit would substantially increase the probability of triggering climate tipping elements. Here, we investigate the tipping risks associated with several policy-relevant future emission scenarios, using a stylised Earth system model of four interconnected climate tipping elements. We show that following current policies this century would commit to a 45% tipping risk by 2300 (median, 10–90% range: 23–71%), even if temperatures are brought back to below 1.5 °C. We find that tipping risk by 2300 increases with every additional 0.1 °C of overshoot above 1.5 °C and strongly accelerates for peak warming above 2.0 °C. Achieving and maintaining at least net zero greenhouse gas emissions by 2100 is paramount to minimise tipping risk in the long term. Our results underscore that stringent emission reductions in the current decade are critical for planetary stability.

Precipitation is essential for food production in Sub-Saharan Africa, where more than 80 % of agriculture is rainfed. Although ∼40 % of precipitation in certain regions is recycled moisture from Africa's tropical rainforest, there needs to be more knowledge about how this moisture supports the continent's agriculture. In this study, we quantify all moisture sources for agrarian precipitation (African agricultural precipitationshed), the estimates of African rainforest's moisture contribution to agricultural precipitation, and the evaporation from agricultural land across the continent. Applying a moisture tracking model (UTRACK) and a dynamic global vegetation model (LPJmL), we find that the Congo rainforest (>60 % tree cover) is a crucial moisture source for many agricultural regions. Although most of the rainforest acreage is in the DRC, many neighboring nations rely significantly on rainforest moisture for their rainfed agriculture, and even in remote places, rainforest moisture accounts for ∼10–20 % of agricultural water use. Given continuous deforestation and climate change, which impact rainforest areas and resilience, more robust governance for conserving the Congo rainforest is necessary to ensure future food production across multiple Sub-Saharan African countries.

The planetary boundaries framework defines a safe operating space for humanity. To date, these boundaries have mostly been investigated separately, and it is unclear whether breaching one boundary can lead to the transgression of another. By employing a dynamic global vegetation model, we systematically simulate the strength and direction of the effects of different transgression levels of the climate change boundary (using climate output from ten phase 6 of the Coupled Model Intercomparison Project models for CO₂ levels ranging from 350 ppm to 1000 ppm). We focus on climate change-induced shifts of Earth's major forest biomes, the control variable for the land-system change boundary, both by the end of this century and, to account for the long-term legacy effect, by the end of the millennium. Our simulations show that while staying within the 350 ppm climate change boundary co-stabilizes the land-system change boundary, breaching it (>450 ppm) leads to critical transgression of the latter, with greater severity the higher the ppm level rises and the more time passes. Specifically, this involves a poleward treeline shift, boreal forest dieback (nearly completely within its current area under extreme climate scenarios), competitive expansion of temperate forest into today's boreal zone, and a slight tropical forest extension. These interacting changes also affect other planetary boundaries (freshwater change and biosphere integrity) and provide feedback to the climate change boundary itself. Our quantitative process-based study highlights the need for interactions to be studied for a systemic operationalization of the planetary boundaries framework.

"Water is the bloodstream of the biosphere" is a wise insight coined by Professor Malin Falkenmark (Falkenmark and Biswas 1995), a world-leading international hydrologist, who passed away on 3 December 2023, at the age of 98 years (Fig. 1). Falkenmark was a scientific visionary, calling for global water stewardship as a fundamental step towards human development, even before modern thinking on sustainable development was established through the 1987 Brundtland Commission and the 1992 Agenda 21 following the United Nations Conference on Environment and Development in Rio. Her lifelong passion was to eradicate water poverty in the world, and to do this with hydrological evidence and inter-disciplinary collaboration. She co-developed the most prestigious award in water science—the Stockholm Water Prize, and received multiple awards herself, including the prestigious Volvo Environment Prize in 1998 and the Blue Planet Award in 2018.

Human actions compromise the many life-supporting functions provided by the freshwater cycle. Yet, scientific understanding of anthropogenic freshwater change and its long-term evolution is limited. Here, using a multi-model ensemble of global hydrological models, we estimate how, over a 145-year industrial period (1861–2005), streamflow and soil moisture have deviated from pre-industrial baseline conditions (defined by 5th–95th percentiles, at 0.5° grid level and monthly timestep over 1661–1860). Comparing the two periods, we find an increased frequency of local deviations on ~45% of land area, mainly in regions under heavy direct or indirect human pressures. To estimate humanity’s aggregate impact on these two important elements of the freshwater cycle, we present the evolution of deviation occurrence at regional to global scales. Annually, local streamflow and soil moisture deviations now occur on 18.2% and 15.8% of global land area, respectively, which is 8.0 and 4.7 percentage points beyond the ~3 percentage point wide pre-industrial variability envelope. Our results signify a substantial shift from pre-industrial streamflow and soil moisture reference conditions to persistently increasing change. This indicates a transgression of the new planetary boundary for freshwater change, which is defined and quantified using our approach, calling for urgent actions to reduce human disturbance of the freshwater cycle.