Future land-use competition constrains natural climate solutions.

Natural climate solutions (NCS) are an essential complement to climate mitigation and have been increasingly incorporated into international mitigation strategies. Yet, with the ongoing population growth, allocating natural areas for NCS may compete with other socioeconomic priorities, especially urban development and food security. Here, we projected the impacts of land-use competition incurred by cropland and urban expansion on the climate mitigation potential of NCS. We mapped the areas available for implementing 9 key NCS strategies and estimated their climate change mitigation potential. Then, we overlaid these areas with future cropland and urban expansion maps projected under three Shared Socioeconomic Pathway (SSP) scenarios (2020-2100) and calculated the resulting mitigation potential loss of each selected NCS strategy. Our results estimate a substantial reduction, 0.3-2.8 GtCO2 yr-1 or 4-39 %, in NCS mitigation potential, of which cropland expansion for fulfilling future food demand is the primary cause. This impact is particularly severe in the tropics where NCS hold the most abundant mitigation potential. Our findings highlight immediate actions prioritized to tropical areas are important to best realize NCS and are key to developing realistic and sustainable climate policies.

Carbon prospecting in tropical forests for climate change mitigation.

Carbon finance projects that protect tropical forests could support both nature conservation and climate change mitigation goals. Global demand for nature-based carbon credits is outpacing their supply, due partly to gaps in knowledge needed to inform and prioritize investment decisions. Here, we show that at current carbon market prices the protection of tropical forests can generate investible carbon amounting to 1.8 (±1.1) GtCO2e yr-1 globally. We further show that financially viable carbon projects could generate return-on-investment amounting to $46.0b y-1 in net present value (Asia-Pacific: $24.6b y-1; Americas: $19.1b y-1; Africa: $2.4b y-1). However, we also find that ~80% (1.24 billion ha) of forest carbon sites would be financially unviable for failing to break even over the project lifetime. From a conservation perspective, unless carbon prices increase in the future, it is imperative to implement other conservation interventions, in addition to carbon finance, to safeguard carbon stocks and biodiversity in vulnerable forests.

Global potential and limits of mangrove blue carbon for climate change mitigation.

Despite the outsized role of mangrove forests in sustaining biodiversity, ecosystem function, and local livelihoods, the protection of these vital habitats through blue carbon financing has been limited.1,2 Here, we quantify the extent of this missed conservation and financial opportunity, showing that the protection of ∼20% of the world's mangrove forests (2.6 Mha) can be funded through carbon financing. Of these investible areas, 1.1-1.3 Mha can be financially sustainable over a 30-year time frame based on carbon prices of US$5-9.4 t-1CO2e. This contributes up to 29.8 MtCO2e year-1 and yields a return on investment of ∼US$3.7 billion per year. Our results point toward a disproportionately large potential of blue carbon finance that can be leveraged to meet national-level climate mitigation goals, particularly if combined with other conservation interventions that further safeguard carbon stocks and biodiversity in these irreplaceable forests. Robust information on return on investment highlights the potential for currently underutilized tropical coastal carbon credit projects.

An open-source dual-beam spectrophotometer for citizen-science-based water quality monitoring.

Efforts to understand and mediate threats to water supplies rely on collection of reliable data at large scale, a goal which is often limited by availability of tools that are both affordable and reliable. We present here a low-cost, easy-to-use, do-it-yourself (DIY) spectrometer for measurement of a variety of relevant solute concentrations when coupled with inexpensive commercially-available reagents. Comparison of its performance with commercial options demonstrates the potential value of this device as transparent, versatile, and accurate-enough alternative for widespread application.