Contrasting influences of biogeophysical and biogeochemical impacts of historical land use on global economic inequality

Local temperature responses to actual land cover changes present significant latitudinal variability and asymmetry

Land cover changes (LCCs) affect surface temperatures at local scale through biophysical processes. However, previous observation-based studies mainly focused on the potential effects of virtual afforestation/deforestation using the space-for-time assumption, while the actual effects of all types of realistic LCCs are underexplored. Here, we adopted the space-and-time scheme and utilized extensive high-resolution (1-km) satellite observations to perform the first such assessment. We showed that, from 2006 to 2015, the average temperature in the areas with LCCs increased by 0.08 K globally, but varied significantly across latitudes, ranging from -0.05 to 0.18 K. Cropland expansions dominated summertime cooling effects in the northern mid-latitudes, whereas forest-related LCCs caused warming effects elsewhere. These effects accounted for up to 44.6% of overall concurrent warming, suggesting that LCC influences cannot be ignored. In addition, we revealed obvious asymmetries in the actual effects, i.e., LCCs with warming effects occurred more frequently, with stronger intensities, than LCCs with cooling effects. Even for the mutual changes between two covers in the same region, warming LCCs generally had larger magnitudes than their cooling counterparts due to asymmetric changes in transition fractions and driving variables. These novel findings, derived from the assessment of actual LCCs, provide more realistic implications for land management and climate adaptation policies.

Temperature Changes Induced by Biogeochemical and Biophysical Effects of Bioenergy Crop Cultivation

The production of bioenergy with carbon capture and storage (BECCS) is a pivotal negative emission technology. The cultivation of dedicated crops for BECCS impacts the temperature through two processes: net CO₂ removal (CDR) from the atmosphere (biogeochemical cooling) and changes in the local energy balance (biophysical warming or cooling). Here, we compare the magnitude of these two processes for key grass and tree species envisioned for large-scale bioenergy crop cultivation, following economically plausible scenarios using Earth System Models. By the end of this century, the cumulative CDR from the cultivation of eucalypt (72-112 Pg C) is larger than that of switchgrass (34-83 Pg C) because of contrasting contributions of land use change carbon emissions. The combined biogeochemical and biophysical effects are cooling (-0.26 to -0.04 °C) at the global scale, but 13-28% of land areas still have net warming signals, mainly due to the spatial heterogeneity of the biophysical effects. Our study shows that the deployment of bioenergy crop cultivation should not only be guided by the principles of maximizing yield and CDR but should also take an integrated perspective that includes all relevant Earth system feedbacks.

Provision of Desalinated Irrigation Water by the Desalination of Groundwater Abstracted from a Saline Aquifer

Globally, about 54 million ha of cropland are irrigated with saline water. Globally, the soils associated with about 1 billion ha are affected by salinization. A small decrease in irrigation water salinity (and soil salinity) can result in a disproportionally large increase in crop yield. This study uses a zero-valent iron desalination reactor to effect surface processing of ground water, obtained from an aquifer, to partially desalinate the water. The product water can be used for irrigation, or it can be reinjected into a saline aquifer, to dilute the aquifer water salinity (as part of an aquifer water quality management program), or it can be injected as low-salinity water into an aquifer to provide a recharge barrier to protect against seawater intrusion. The saline water used in this study is processed in a batch flow, bubble column, static bed, diffusion reactor train (0.24 m3), with a processing capacity of 1.7–1.9 m3 d−1 and a processing duration of 3 h. The reactor contained 0.4 kg Fe0. A total of 70 batches of saline water (average 6.9 g NaCl L−1; range: 2.66 to 30.5 g NaCl L−1) were processed sequentially using a single Fe0 charge, without loss of activity. The average desalination was 24.5%. The reactor used a catalytic pressure swing adsorption–desorption process. The trial results were analysed with respect to Na+ ion removal, Cl− ion removal, and the impact of adding trains. The reactor train was then repurposed, using n-Fe0 and emulsified m-Fe0, to establish the impact of reducing particle size on the amount of desalination, and the amount of n-Fe0 required to achieve a specific desalination level.