Non-perennial river segments - those that recurrently cease to flow or frequently dry - occur in all river networks and are globally more abundant than perennial (always flowing) segments. However, research and management have historically focused on perennial river segments. In this Review, we outline how non-perennial segments are integral parts of river networks. Repeated cycles of flowing, non-flowing and dry phases in non-perennial segments influence biodiversity and ecosystem dynamics at different spatial scales, from individual segments to entire river networks. Varying configurations of perennial and non-perennial segments govern physical, chemical and ecological responses to changes in the flow regimes of each river network, especially in response to human activities. The extent of non-perennial segments in river networks has increased owing to warming, changing hydrological patterns and human activities, and this increase is predicted to continue. Moreover, the dry phases of flow regimes are expected to be longer, drier and more frequent, albeit with high regional variability. These changes will likely impact biodiversity, potentially tipping some ecosystems to compromised stable states. Effective river-network management must recognize ecosystem services (such as flood risk management and groundwater recharge) provided by non-perennial segments and ensure their legislative and regulatory protection, which is often lacking.

Increasing salt production and use is shifting the natural balances of salt ions across Earth systems, causing interrelated effects across biophysical systems collectively known as freshwater salinization syndrome. In this Review, we conceptualize the natural salt cycle and synthesize increasing global trends of salt production and riverine salt concentrations and fluxes. The natural salt cycle is primarily driven by relatively slow geologic and hydrologic processes that bring different salts to the surface of the Earth. Anthropogenic activities have accelerated the processes, timescales and magnitudes of salt fluxes and altered their directionality, creating an anthropogenic salt cycle. Global salt production has increased rapidly over the past century for different salts, with approximately 300 Mt of NaCl produced per year. A salt budget for the USA suggests that salt fluxes in rivers can be within similar orders of magnitude as anthropogenic salt fluxes, and there can be substantial accumulation of salt in watersheds. Excess salt propagates along the anthropogenic salt cycle, causing freshwater salinization syndrome to extend beyond freshwater supplies and affect food and energy production, air quality, human health and infrastructure. There is a need to identify environmental limits and thresholds for salt ions and reduce salinization before planetary boundaries are exceeded, causing serious or irreversible damage across Earth systems.

Environmental cycling of microplastics and nanoplastics is complex; fully understanding these pollutants is hindered by inconsistent methodologies and experimentation within a narrow scope. Consistent methods are needed to advance plastic research and policy within the context of global environmental change.

Soil health is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans, and connects agricultural and soil science to policy, stakeholder needs and sustainable supply chain management. Historically, soil assessments focused on crop production, but today soil health also includes the role of soil in water quality, climate change and human health. However, quantifying soil health is still dominated by chemical indicators, despite growing appreciation of the importance of soil biodiversity, due to limited functional knowledge and lack of effective methods. In this Perspective, the definition and history of soil health are described and compared to other soil concepts. We outline ecosystem services provided by soils, the indicators used to measure soil functionality, and their integration into informative soil health indices. Scientists should embrace soil health as an overarching principle that contributes to sustainability goals, rather than only a property to measure.

Owing to a lack of understanding, and data being unavailable, unusable or unsuitable, weather and climate information is currently underutilized in Sustainable Development Goal implementation. Improvements are essential in knowledge brokering, clarifying responsibilities, multi-institutional and multi-stakeholder governance arrangements and research on systemic risks and decisions.

The COVID-19 pandemic is exacerbating plastic pollution. A shift in waste management practices is thus urgently needed to close the plastic loop, requiring governments, researchers and industries working towards intelligent design and sustainable upcycling.

Following record-level declines in 2020, near-real-time data indicate that global CO emissions rebounded by 4.8% in 2021, reaching 34.9 GtCO. These 2021 emissions consumed 8.7% of the remaining carbon budget for limiting anthropogenic warming to 1.5 °C, which if current trajectories continue, might be used up in 9.5 years at 67% likelihood.

Global CO emissions for 2022 increased by 1.5% relative to 2021 (+7.9% and +2.0% relative to 2020 and 2019, respectively), reaching 36.1 GtCO. These 2022 emissions consumed 13%-36% of the remaining carbon budget to limit warming to 1.5 °C, suggesting permissible emissions could be depleted within 2-7 years (67% likelihood).

The 2023 Kahramanmaraş earthquakes occurred on active faults that were known to be a high seismic hazard, yet the devastating impacts of these earthquakes show that the risk was not adequately considered. Vulnerabilities arising from exposure, corruption and poverty led to a lack of seismic preparedness which amplified the earthquake risk into a tragic disaster.