China’s Belt and Road Initiative (BRI) is the largest infrastructure scheme in our lifetime, bringing unprecedented geopolitical and economic shifts far larger than previous rising powers. Concerns about its environmental impacts are legitimate and threaten to thwart China’s ambitions, especially since there is little precedent for analysing and planning for environmental impacts of massive infrastructure development at the scale of BRI. In this paper, we review infrastructure development under BRI to characterise the nature and types of environmental impacts and demonstrate how social, economic and political factors can shape these impacts. We first address the ambiguity around how BRI is defined. Then we describe our interdisciplinary framework for considering the nature of its environmental impacts, showing how impacts interact and aggregate across multiple spatiotemporal scales creating cumulative impacts. We also propose a typology of BRI infrastructure, and describe how economic and socio-political drivers influence BRI infrastructure and the nature of its environmental impacts. Increasingly, environmental policies associated with BRI are being designed and implemented, although there are concerns about how these will translate effectively into practice. Planning and addressing environmental issues associated with the BRI is immensely complex and multi-scaled. Understanding BRI and its environment impacts is the first step for China and countries along the routes to ensure the assumed positive socio-economic impacts associated with BRI are sustainable.

The climate mitigation potential of urban nature-based solutions (NBSs) is often perceived as insignificant and thus overlooked, as cities primarily pursue NBSs for local ecosystem services. Given the rising interest and capacities in cities for such projects, the potential of urban forests for climate mitigation needs to be better understood. We modelled the global potential and limits of urban reforestation worldwide, and find that 10.9 ± 2.8 Mha of land (17.6% of all city areas) are suitable for reforestation, which would offset 82.4 ± 25.7 MtCO₂e yr⁻¹ of carbon emissions. Among the cities analysed, 1189 are potentially able to offset >25% of their city carbon emissions through reforestation. Urban natural climate solutions should find a place on global and local agendas.

Indonesia’s new planned capital in East Kalimantan is being touted as a “smart, green, beautiful and sustainable city” but has stoked fears of massive environmental damage to the island of Borneo, one of the world’s most important biodiversity hotspots and carbon sinks. Precedents of other planned capitals can contribute to an understanding of the potential long-term impacts of Indonesia’s new capital. We used historical nighttime lights to quantitatively assess the spatial growth footprint of 12 previous planned capitals, and conducted land-use analyses to identify the potential environmental impacts on Borneo’s natural environment. Our assessment suggests that it is likely that the direct footprint of the new capital could grow rapidly, expanding over 10 km from its core in less than two decades and over 30 km before mid-century. We identified sensitive ecosystems which may be affected by the new capital’s direct and indirect footprint, such as forest reserves, mangrove and peat. Deforestation emissions from the new capital’s direct (30 km) and indirect (200 km) footprint could be approximately 50 MtCO_2e and 2326 MtCO_2e respectively, equivalent to 2.7% and 126% of Indonesia’s 2014 greenhouse gas emissions. We discuss how planned capitals can spatially restructure the socio-political geographies of cities and nation-states by interacting with meanings, symbolisms and power relations, which may aggravate environmental impacts but also be seized upon as a catalyst for improving environmental performance in Borneo and Indonesia. Finally, we recommend the use of best practices in impact assessment and sustainability as a necessary first step towards protecting Borneo.

Plant phenology is closely related to light availability as diurnal and seasonal cycles are essential environmental cues for organizing bio-ecological processes. The natural cycles of light, however, have been dramatically disrupted by artificial light at night (ALAN) due to recent urbanization. The influence on plant phenology of ALAN and its spatial variation remain largely unknown. By analyzing satellite data on ALAN intensity across the United States, here, we showed that ALAN tended to advance the start date of the growing season (SOS), although the overall response of SOS to ALAN was relatively weak compared with other potential factors (e.g., preseason temperature). The phenological impact of ALAN showed a spatially divergent pattern, whereby ALAN mainly advanced SOS at climatically moderate regions within the United States (e.g., Virginia), while its effect was insignificant or even reversed at very cold (e.g., Minnesota) and hot regions (e.g., Florida). Such a divergent pattern was mainly attributable to its high sensitivity to chilling insufficiency, where the advancing effect on SOS was only triggered on the premise that chilling days exceeded a certain threshold. Other mechanisms may also play a part, such as the interplay among chilling, forcing and photoperiod and the difference in species life strategies. Besides, urban areas and natural ecosystems were found to suffer from similar magnitudes of influence from ALAN, albeit with a much higher baseline ALAN intensity in urban areas. Our findings shed new light on the phenological impact of ALAN and its relation to space and other environmental cues, which is beneficial to a better understanding and projection of phenology changes under a warming and urbanizing future.