• Energy Research

AbstractStability of the soil carbon (C) pool under decadal scale variability in temperature and precipitation is an important source of uncertainty in our understanding of land–atmosphere climate feedbacks. This depends on how two opposing C‐fluxes—influx from net primary production (NPP) and efflux from heterotrophic soil respiration (Rh)—respond to covariation in temperature and precipitation. There is scant evidence to judge whether field experiments which manipulate both temperature and precipitation align with Earth System Models, or not. As a result, even though the world is generally greening, whether the resultant gains in NPP can offset climate change impacts on Rh, where, and by how much, remains uncertain. Here, we use decadal‐scale global time‐series datasets on NPP, Rh, temperature, and precipitation to estimate the two opposing C‐fluxes and address whether one can outpace the other. We implement machine‐learning tools on recent (2001–2019) and near‐future climate scenarios (2020–2040) to assess the response of both C‐fluxes to temperature and precipitation variation. We find that changes in C‐influx may not compensate for C‐efflux, particularly in wetter and warmer conditions. Soil‐C loss can occur in both tropics and at high latitudes since C‐influx from NPP can fall behind C‐efflux from Rh. Precipitation emerges as the key determinant of soil‐C vulnerability in a warmer world, implying that hotspots for soil‐C loss/gain can shift rapidly and highlighting that soil‐C is vulnerable to climate change despite widespread greening of the world. The direction of covariation between change in temperature and precipitation, rather than their magnitude, can help conceptualize highly variable patterns in C‐fluxes to guide soil‐C stewardship.

AbstractCities, despite being responsible for the loss of habitat as they grow, are also an important refugium for biodiversity. Many urban areas in the tropical areas of the global south are rich in biodiversity and are also undergoing climate warming and heat island impacts. Eliciting support from policy and decision makers for sustaining the habitats for birds in cities may depend on how conservation of bird habitats is linked to the new emphasis on ecosystem services, including heat stress mitigation. The megacity of Bengaluru has over 350 species of birds that are found in diverse habitats that include urban forests, large institutional campuses, gardens, and parks. Based on existing literature, we a priori predicted that parts of the city with higher levels of heat will have lower bird presences and parts with higher green cover are likely to support higher presences of birds, while allowing for some birds to prefer open habitats with less greenness. We tested hypotheses on the role of green cover and heat stress on bird occurrence using an informed Bayesian regression approach. We summarized the information and uncertainty on the direction of the slope of the two covariates as hyper priors as inputs to the regression. We used satellite data on heat stress as a proxy for urban heat islands and climate warming effects, and green cover (Normalized Difference Vegetation Index [NDVI]), to test their effects on spatially explicit occurrences of urban birds. We found that all birds responded negatively to the hotter parts of the city, but the effects of green cover varied (negative, neutral and positive) with species identity (Pseudo‐R2 0.13–0.36). This could partially be due to the preference for open spaces or dependence on anthropogenic food sources for foraging by these species. We mapped heat islands, cooling potential, and the bird diversity of green spaces in Bengaluru to identify areas of conservation value that also help mitigate heat stress for citizens. Going forward, these results can help us answer nuanced species‐level responses and their vulnerability to the impacts of climate change and foster support for conservation of bird habitats in Bengaluru.

Global change is associated with variable shifts in the annual production of aboveground plant biomass, suggesting localized sensitivities with unclear causal origins. Combining remotely sensed normalized difference vegetation index data since the 1980s with contemporary field data from 84 grasslands on 6 continents, we show a widening divergence in site-level biomass ranging from +51% to -34% globally. Biomass generally increased in warmer, wetter and species-rich sites with longer growing seasons and declined in species-poor arid areas. Phenological changes were widespread, revealing substantive transitions in grassland seasonal cycling. Grazing, nitrogen deposition and plant invasion were prevalent in some regions but did not predict overall trends. Grasslands are undergoing sizable changes in production, with implications for food security, biodiversity and carbon storage especially in arid regions where declines are accelerating.