Global Change Biology最新文献

Assisted colonization (AC), translocating a species outside its indigenous range to avoid its extinction, is one of the few conservation options for some species. It is also controversial because of the history of ecological impacts of invasive species, including the extinction of native species as a result of novel ecological interactions resulting from the introduction. Although several national and international organizations have issued guidelines related to AC, none allow case-specific decision-making based on risks and benefits to biodiversity. We propose a two-pronged approach to fill this gap. The first step aims to separate clear-cut cases of AC from those that require an in-depth risk analysis. We propose a set of seven qualitative criteria to identify AC projects that are clearly low-risk and high-benefit, and therefore should not be controversial, and those that are clearly high-risk or low-benefit and therefore should not be attempted. This identifies only the most obvious cases, leaving out many cases to be determined through a quantitative analysis to estimate the probabilities of extirpation of the resident species because of AC, which is the second step of our approach. We propose a roadmap for developing such a system based on community ecology theory, and a framework for considering the estimated probabilities in a global context. Our framework recommends an AC project only if it would result in a larger number of globally extant species than a scenario of no action. We propose large-scale testing of the clear-cut approach, further development of the quantitative approach, and wide consultation for adopting international guidelines for risk assessment of AC projects.

Despite repeated increases in national climate pledges since the Paris Agreement, a significant gap remains between collective ambition and the action required to meet its temperature goals. Integrating these pledges with global models, we show that full implementation would still lead to approximately 1.7°C of warming, missing the 1.5°C target. When considering ongoing policy inaction, a cumulative shortfall of 505 GtCO₂e in anticipated mitigation is expected, and this warming increases by nearly 0.3°C, drastically narrowing the window to stay below 2.0°C. Our analysis reveals a critical disparity on a regional level: High-income nations are often meeting modest targets, while low-income countries face capacity constraints in delivering ambitious pledges. This imbalance underscores that persistent inequities in responsibility and resources are undermining global climate effectiveness. Closing the ambition–credibility gap urgently requires enhanced international cooperation and support to ensure a viable pathway for all.

Raptors—a group that includes hawks, eagles, owls, and vultures—are among the most imperiled vertebrates, with over half of species declining and one-fifth threatened with extinction. Most raptors depend on forests for survival, yet the extent and consequences of recent deforestation within their ranges remain poorly understood. We analyzed high-resolution global data on forest change between 2001 and 2023 within the ranges of 369 forest-dependent raptor species. On average, these species have lost 10% of forest within their ranges since 2001. Seventy-seven species had already lost at least 15% of additional forest cover within their ranges in the latter half of the 20th century. Currently, only 52% of forest cover remains within forest-dependent species' ranges on average, with many forest specialists retaining less than 25% cover. Forest-dependent raptors listed as Critically Endangered by the IUCN have lost the most forest and now retain the least forest cover within their ranges. Shifting agriculture is the primary driver of forest loss—particularly in tropical Africa and South America—followed by commodity-driven deforestation in Southeast Asia. Because forest loss is frequently used as a proxy for extinction risk for raptors, our findings have direct applications for species threat assessments, regional conservation priorities, and global biodiversity commitments.

Anthropogenic change is predicted to result in widespread declines in insect abundance, but assessing long-term trends is challenging due to the scarcity of systematically collected time series measurements across large spatial scales. We develop a novel continental-scale dataset using a nationwide network of radars in the United States to generate a 10-year time series of daily aerial insect density and assess temporal trends. We do not find evidence of a continental-scale net decline in insect density over the 10-year period included in this study; instead we find a mosaic of increasing and declining trends at the landscape scale. This spatial variation in density trends is associated with climatic drivers, where areas with warmer winters experience greater declines in insect density and areas with cooling winter trends see increases in density. Winter warming has a stronger negative effect on density at higher latitudes. After assessing temporal trends, we also use the 10-year dataset and atmospheric variables to model insect aerial abundance, finding that on a typical summer day approximately a hundred trillion (10¹⁴) flying insects are present in the airspace, representing millions of tons of aerial biomass. Our results provide the first continental-scale quantification of insect density and its response to anthropogenic warming and demonstrate the utility of weather surveillance radar to provide large-scale monitoring of insect abundance.

The rising threat of marine heatwaves has led to numerous predictions that coral reefs, especially those near the Equator, will be severely degraded by the end of the current century. Yet, environmental conditions near the Equator may regionally moderate coral bleaching by reducing thermal stress during marine heatwaves. We deployed a Bayesian spatio-temporal model over Earth to examine which environmental conditions may characterize marine-heatwave refugia for coral reefs by testing the relationship between the severity of coral bleaching and a suite of temperature, hydrodynamic, topographic, atmospheric, and biological variables. The model considered the severity of coral bleaching as the proportion of bleached hard corals during 30,266 coral-reef surveys conducted at 8728 sites, at depths of up to 20 m, and located between 35° north and south of the Equator across 81 countries, from 2002 to 2020. Except for the eastern Pacific Ocean, the severity of coral bleaching during marine heatwaves was lower on equatorial reefs than on higher-latitude reefs, suggesting that marine-heatwave refugia for corals have been concentrated in the equatorial Coral Triangle region. Indeed, equatorial reefs in the Coral Triangle were, on average, exposed to the weakest marine heatwaves, potentially because they were shielded from extreme insolation by frequent cloud coverage in the Intertropical Convergence Zone. Coral bleaching may also be moderated during marine heatwaves on reefs that experience high wave energy, high current velocity, high cloud frequency, or turbidity. Coral bleaching was also less severe on reefs that historically endured frequent heatwaves than on reefs that were naïve to thermal stress. Based on modern and historical responses of coral reefs to acute thermal stress, we hypothesize that many equatorial reefs will continue to serve as marine-heatwave refugia for corals.

Stomatal conductance (g_s) regulates CO₂ and water fluxes of plants. Although experiments have shown that g_s decreases with elevated CO₂, it is unclear how g_s is responding in situ to long-term exposures to rising CO₂ and a changing climate. Tree ring isotope analysis provides a unique method to assess tree ecophysiological responses to long-term exposures of slowly changing environmental conditions. In particular, it has been suggested that changes in g_s can potentially be inferred from tree ring stable oxygen isotope ratios (δ¹⁸O_trc). Several studies have indeed used δ¹⁸O_trc trends to conclude that g_s has not significantly changed from pre-industrial values. However, it remains unclear whether δ¹⁸O_trc is sufficiently sensitive to detect the magnitude of change in g_s expected due to CO₂ increases and climatic changes. Here, we evaluate the sensitivity of δ¹⁸O_trc trends to CO₂ and climate induced changes in g_s, and to VPD and temperature increases since the beginning of the 20th century, using current theoretical models. We find that temporal changes in g_s only significantly affect δ¹⁸O_trc trends when the Péclet effect is present, and then only in dry climates. In contrast to the weak effects of g_s on δ¹⁸O_trc trends, we find that temporal increases in VPD and temperature, independent of changes in g_s, have far greater contributions to δ¹⁸O_trc trends. Thus, this increasingly popular method should be used with caution, because it is highly challenging to unambiguously attribute trends in δ¹⁸O_trc to changes in g_s. Despite current limitations, we recommend how future studies can address these challenges in efforts to detect long-term g_s trends from tree ring records.

Rising CO₂ levels indirectly affect food availability (e.g., through climate shifts, biological consequences, and shifting socioeconomic systems). Less known is the direct effect of CO₂ on nutrient availability by changing the plant stoichiometry. We help fill this gap, presenting a new methodology and creating the largest meta-analysis on edible plant parts to date, including the most data (5324 entries covering 29,524 observation pairs), crops (43), and (anti)nutrients (32). The results show a pervasive elemental shift across a wide range of species as CO₂ rises. Elements respond differentially, with zinc decreasing the most. Plants with not only a C3 but also a C4 photosynthetic pathway respond. Impacts vary by species and tissue type. This stoichiometric shift can lead to (worsening) malnutrition even in previously sufficient populations. Nutrient security is under threat even if food security remains adequate; food will become more caloric and less nutritious.