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 pressures have pushed the Earth system deep into the Anthropocene, threatening its stability, resilience and functioning. The Planetary Boundaries (PB) framework emerged against these threats, setting safe levels to the biophysical systems and processes that, with high likelihood, ensure life-supporting Holocene-like conditions. In this Review, we synthesize PB advancements, detailing its emergence and mainstreaming across scientific disciplines and society. The nine PBs capture the key functions regulating the Earth system. The safe operating space has been transgressed for six of these. PB science is essential to prevent further Earth system risks and has sparked new research on the precision of safe boundaries. Human development within planetary boundaries defines sustainable development, informing advances in social sciences. Each PB translates to a finite budget that the world must operate within, requiring strengthened global governance. The PB framework has been adopted by businesses and informed policy across the world, informing new thinking about fundamental justice concerns, and has inspired, among other concepts, the planetary commons, planetary health and doughnut economics. Future work must increase the precision and frequency of PB analyses, and, together with Earth observation data analytics, produce a high-resolution and real-time state of planetary health.

Mounting evidence of accelerating global environmental change is driving scientists to question whether we are witnessing a breakdown in the resilience of our planet. Three lines of scientific enquiry have been important when studying the stability and resilience of the planet: the empirical evidence of the great acceleration of the human enterprise from the 1950s onwards resulting in planetary-scale pressures; the understanding that Earth is a complex biosphere-geosphere system with self-regulating interactions and feedbacks contributing to control its equilibrium state; and the emerging insight into the unique stability of the Holocene Epoch, the last 10,000 years of inter-glacial equilibrium, and its critical role in providing predictable (and for humanity agreeable) life conditions for the evolution of modern civilizations. Professor Will Steffen played a pivotal role in integrating and advancing these three Earth system research avenues and combining them into one integrated people-planet framework Earth system. State-of-the-art research on fully coupled Earth system models (ESMs) that also integrate non-linear dynamics and tipping-point behavior, and even human dynamics, is built in part on Will Steffen's pioneering work to observe and describe the Earth in the Anthropocene.

The Anthropocene signifies the start of a no-analogue trajectory of the Earth system that is fundamentally different from the Holocene. This new trajectory is characterized by rising risks of triggering irreversible and unmanageable shifts in Earth system functioning. We urgently need a new global approach to safeguard critical Earth system regulating functions more effectively and comprehensively. The global commons framework is the closest example of an existing approach with the aim of governing biophysical systems on Earth upon which the world collectively depends. Derived during stable Holocene conditions, the global commons framework must now evolve in the light of new Anthropocene dynamics. This requires a fundamental shift from a focus only on governing shared resources beyond national jurisdiction, to one that secures critical functions of the Earth system irrespective of national boundaries. We propose a new framework—the planetary commons—which differs from the global commons framework by including not only globally shared geographic regions but also critical biophysical systems that regulate the resilience and state, and therefore livability, on Earth. The new planetary commons should articulate and create comprehensive stewardship obligations through Earth system governance aimed at restoring and strengthening planetary resilience and justice. 

This planetary boundaries framework update finds that six of the nine boundaries are transgressed, suggesting that Earth is now well outside of the safe operating space for humanity. Ocean acidification is close to being breached, while aerosol loading regionally exceeds the boundary. Stratospheric ozone levels have slightly recovered. The transgression level has increased for all boundaries earlier identified as overstepped. As primary production drives Earth system biosphere functions, human appropriation of net primary production is proposed as a control variable for functional biosphere integrity. This boundary is also transgressed. Earth system modeling of different levels of the transgression of the climate and land system change boundaries illustrates that these anthropogenic impacts on Earth system must be considered in a systemic context.

An on-farm field experiment on a locally adapted conservation tillage method was undertaken to evaluate its effect on soil erosion, surface runoff, and agronomic parameters. It was conducted on five farmer fields with 3–14% slopes in the Rift Valley and the Eastern escarpment of Ethiopia’s central highlands region for two cropping seasons. The treatments were conventional tillage (CT), repeated ploughing performed with a traditional ox-drawn plough named ‘Maresha’, and minimized contour ploughing (MT) at most twice with a locally adapted sweep-like attachment assembled to Maresha. Surface runoff and soil loss in the MT system were 30 to 60% and 49 to 76% lower than those in the CT system on 3 to 14% slopes, respectively. Despite the wide variation in surface runoff, limited differences in soil water content for the depth from 0 to 20 cm were observed between the treatments. Significant differences (p < 0.05) in grain yields (kg ha⁻¹) of 246 and 323 in the 1st and 2nd growing seasons, respectively, were recorded between the MT and CT treatments. The results of this study demonstrated that the MT system can significantly reduce surface runoff and soil loss while improving crop yields in rainfed smallholder farming systems of Ethiopia.