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Mesoscale ocean eddies, an important element of the climate system, impact ocean circulation, heat uptake, gas exchange, carbon sequestration and nutrient transport. Much of what is known about ongoing changes in ocean eddy activity is based on satellite altimetry; however, the length of the altimetry record is limited, making it difficult to distinguish anthropogenic change from natural variability. Using a climate model that exploits a variable-resolution unstructured mesh in the ocean component to enhance grid resolution in eddy-rich regions, we investigate the long-term response of ocean eddy activity to anthropogenic climate change. Eddy kinetic energy is projected to shift poleward in most eddy-rich regions, to intensify in the Kuroshio Current, Brazil and Malvinas currents and Antarctic Circumpolar Current and to decrease in the Gulf Stream. Modelled changes are linked to elements of the broader climate including Atlantic meridional overturning circulation decline, intensifying Agulhas leakage and shifting Southern Hemisphere westerlies.Anthropogenic changes in ocean eddies are difficult to distinguish from natural variability due to short satellite records. Here model projections show a poleward shift and intensification of eddy kinetic energy in most eddy-rich regions; however, Gulf Stream eddy activity decreases.

Given the possibility of irreversible, anthropogenic changes in the climate system, technologies such as solar radiation management (SRM) are sometimes framed as possible emergency interventions. However, little knowledge exists on the efficacy of such deployments. To fill in this gap, we perform Community Earth System Model 2 simulations of an intense warming scenario on which we impose gradual early‐century SRM or rapid late‐century cooling (an emergency intervention), both realized via stratospheric aerosol injection (SAI). While both scenarios cool Earth's surface, ocean responses differ drastically. Rapid cooling fails to release deep ocean heat content or restore an ailing North Atlantic deep convection but partially stabilizes the Atlantic meridional overturning circulation. In contrast, the early intervention effectively mitigates changes in all of these features. Our results suggest that slow ocean timescales impair the efficacy of some SAI emergency interventions. Plain Language Summary Stratospheric aerosol injection (SAI) is a promising, yet controversial proposal to mask the effects of anthropogenic climate change by releasing sunlight‐reflecting particles into the atmosphere. Currently, many studies are focusing on the benefits of near future SAI deployments. We, however, investigate SAI as a late emergency intervention. To what extent can SAI still help if we continue to heat and destabilize the climate? In this study, we simulate the impacts of an abrupt, SAI cooling intervention deployed against the backdrop of a climate much hotter than today's. While SAI readily cools Earth's surface, it is challenged by a slow ocean response. Heat trapped below the ocean surface remains a contributor to sea‐level rise and important currents weakened by climate change linger in ailing condition. In contrast, an earlier SAI intervention effectively mitigates changes in these features. Our findings re‐emphasize the urgent need for climate action. If anthropogenic heating continues, even an intervention as powerful as SAI will encounter its limits. Key Points Efficacy of stratospheric aerosol injection (SAI) impaired by anthropogenic ocean heating Deep ocean heating, weakened Atlantic Meridional Overturning Circulation (AMOC) and collapsed North Atlantic deep convection only partially addressed by late SAI SAI decouples AMOC and global mean surface temperature, thereby inducing climate states not seen in purely greenhouse gas‐forced scenarios

Water management measures in the 1970s in the Netherlands have produced a large number of “resident” populations of three-spined sticklebacks that are no longer able to migrate to the sea. This may be viewed as a replicated field experiment, allowing us to study how the resident populations are coping with human-induced barriers to migration. We have previously shown that residents are smaller, bolder, more exploratory, more active, and more aggressive and exhibited lower shoaling and lower migratory tendencies compared to their ancestral “migrant” counterparts. However, it is not clear if these differences in wild-caught residents and migrants reflect genetic differentiation, rather than different developmental conditions. To investigate this, we raised offspring of four crosses (migrant ♂ × migrant ♀, resident ♂ × resident ♂, migrant ♂ × resident ♀, resident ♂ × migrant ♀) under similar controlled conditions and tested for differences in morphology and behavior as adults. We found that lab-raised resident sticklebacks exhibited lower shoaling and migratory tendencies as compared to lab-raised migrants, retaining the differences in their wild-caught parents. This indicates genetic differentiation of these traits. For all other traits, the lab-raised sticklebacks of the various crosses did not differ significantly, suggesting that the earlier-found contrast between wild-caught fish reflects differences in their environment. Our study shows that barriers to migration can lead to rapid differentiation in behavioral tendencies over contemporary timescales (~ 50 generations) and that part of these differences reflects genetic differentiation.

The Great Basin is home to a variety of avian species but as anthropogenic change continues, land cover change in this region may displace some species. We quantified the amount of land cover change in the Great Basin region between 2001 and 2019, analyzed distribution data derived from the eBird Status and Trends database for 19 raptor species (orders Accipitriformes and Falconiformes), and identified each species' land cover occurrence patterns. We discovered that 15 of the raptor species investigated had land cover type as a top-10 predictor for occupancy. We also observed a large percent change in total cover of water, deciduous forest, mixed forest, shrublands, and grasslands land cover types. The raptor species with land cover in their top-10 predictor list could thus potentially be affected by these land cover change trends. While the complexity of land cover associations are nuanced, we identify patterns of land cover change over almost 2 decades in the Great Basin and reveal species that may be impacted by continued landscape change. These findings can provide crucial information for both habitat management and species conservation. El Great Basin (en el occidente de los Estados Unidos) es hábitat para una variedad de especies de aves, aunque el cambio antropogénico sostenido en la cobertura del suelo en esta región podría desplazar a algunas especies. Cuantificamos la suma de cambio en la cobertura del suelo en la región del Great Basin entre 2001–2019, analizamos la distribución derivada de la base de datos eBird Status and Trends para 19 especies de rapaces (órdenes Accipitriformes y Falconiformes) e identificamos los patrones de presencia por cobertura de cada especie. Descubrimos que 15 de especies de rapaces que investigamos tenían la cobertura del suelo como una de las 10 principales variables de ocupación. También observamos un gran porcentaje de cambio en la superficie total de los tipos de cobertura agua, bosque deciduo, bosque mixto, matorral y pradera. Las especies de rapaces con cobertura del suelo en su lista de las 10 principales variables predictivas podrían ser potencialmente afectadas por esas tendencias en cambio de la cobertura del suelo. Si bien la complejidad de las asociaciones de cobertura del suelo es ambigua, identificamos patrones de cambio de cobertura a lo largo de cerca de 2 décadas en el Great Basin y revelan especies que podrían estar impactadas por un continuo cambio en el paisaje. Estos hallazgos proveen información crucial para el manejo de hábitat y la conservación de especies. Palabras clave: aves de presa, cambio antropogénico, cambio de uso del suelo, ciencia comunitaria, desertificación.

An attribution study has been performed to investigate the degree to which the unusually cold European winter of 2009/10 was modified by anthropogenic climate change. Two different methods have been included for the attribution: one based on large HadGEM3-A ensembles and one based on a statistical surrogate method. Both methods are evaluated by comparing simulated winter temperature means, trends, standard deviations, skewness, return periods, and 5% quantiles with observations. While the surrogate method performs well, HadGEM3-A in general underestimates the trend in winter by a factor of ⅔. It has a mean cold bias dominated by the mountainous regions and also underestimates the cold 5% quantile in many regions of Europe. Both methods show that the probability of experiencing a winter as cold as 2009/10 has been reduced by approximately a factor of 2 because of anthropogenic changes. The method based on HadGEM3-A ensembles gives somewhat larger changes than the surrogate method because of differences in the definition of the unperturbed climate. The results are based on two diagnostics: the coldest day in winter and the largest continuous area with temperatures colder than twice the local standard deviation. The results are not sensitive to the choice of bias correction except in the mountainous regions. Previous results regarding the behavior of the measures of the changed probability have been extended. The counterintuitive behavior for heavy-tailed distributions is found to hold for a range of measures and for events that become more rare in a changed climate.

Anthropogenic greenhouse gas emissions cause ocean warming and oxygen depletion, with adverse impacts on marine organisms and ecosystems. Warming is one of the main indicators of anthropogenic climate change, but, in the thermocline, changes in oxygen and other biogeochemical tracers may emerge from the bounds of natural variability prior to warming. Here, we assess the time of emergence (ToE) of anthropogenic change in thermocline temperature and thermocline oxygen within an ensemble of Earth system model simulations from the fifth phase of the Coupled Model Intercomparison Project. Changes in temperature typically emerge from internal variability prior to changes in oxygen. However, in about a third (35±11 %) of the global thermocline deoxygenation emerges prior to warming. In these regions, both reduced ventilation and reduced solubility add to the oxygen decline. In addition, reduced ventilation slows the propagation of anthropogenic warming from the surface into the ocean interior, further contributing to the delayed emergence of warming compared to deoxygenation. Magnitudes of internal variability and of anthropogenic change, which determine ToE, vary considerably among models leading to model–model differences in ToE. We introduce a new metric, relative ToE, to facilitate the multi-model assessment of ToE. This reduces the inter-model spread compared to the traditionally evaluated absolute ToE. Our results underline the importance of an ocean biogeochemical observing system and that the detection of anthropogenic impacts becomes more likely when using multi-tracer observations.

Anthropogenic climate change has triggered impacts on natural and human systems world-wide, yet the formal scientific method of detection and attribution has been only insufficiently described. Detection and attribution of impacts of climate change is a fundamentally cross-disciplinary issue, involving concepts, terms, and standards spanning the varied requirements of the various disciplines. Key problems for current assessments include the limited availability of long-term observations, the limited knowledge on processes and mechanisms involved in changing environmental systems, and the widely different concepts applied in the scientific literature. In order to facilitate current and future assessments, this paper describes the current conceptual framework of the field and outlines a number of conceptual challenges. Based on this, it proposes workable cross-disciplinary definitions, concepts, and standards. The paper is specifically intended to serve as a baseline for continued development of a consistent cross-disciplinary framework that will facilitate integrated assessment of the detection and attribution of climate change impacts.

Comprehending the causal relationships between shifting climatic patterns, dynamic vegetation cover, and altered hydrological cycles constitutes a fundamental prerequisite for developing adaptive strategies in water resources governance. We analyze changes in baseflow (BF) and stormflow (SF) in 3,388 watersheds globally in the response to changes in precipitation characteristics, vegetation (Normalized Difference Vegetation Index, NDVI), temperature, potential evapotranspiration, and the aridity index from 1982 to 2016, based on Random Forest Model simulations and Shapley Additive Explanations. We also evaluate the effects of anthropogenic climate change on changes in baseflow index (BFI, the ratio of baseflow to total streamflow) using the signal‐to‐noise ratio (SNR) method applied to multi‐model simulations from ISIMIP2b. Results show that the BF and SF in the majority of watersheds show consistent trends, but they also show the opposite trends in specific seasons. Over 60% of watersheds in the Northern Hemisphere experienced a decrease in BF contribution to the total streamflow during the June‐July‐August season. Minimum temperature and NDVI are the most important factors influencing changes in BF and SF. Minimum and maximum temperature, precipitation seasonality, and precipitation intensity show negative effects on the BF, and the impact of vegetation on the BFI varies from region to region. The contribution of BF to the total streamflow decreases significantly at the global scale under the impact of anthropogenic climate change, according to the SNR analysis. The interaction of climate and vegetation changes on changes in BF and SF should take into account to regional adaptation of climate change for the utilization of groundwater and surface water resources.

Pacific decadal variability (PDV), reflected in low‐frequency Pacific sea surface temperature (SST) changes, impacts global climate. Disentangling anthropogenic effects upon PDV is challenging because PDV and anthropogenic forcing vary on similar time scales. Using single‐forcing climate model large ensembles, we find that anthropogenic forcing drives a spatially varying pattern of mean‐state change in Pacific SST that projects onto PDV patterns, principally the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). When the trend is removed by subtracting the ensemble mean, there is no forced change of either PDV mode. However, analysis of individual ensemble members, where the mean‐state trend cannot be cleanly removed, yields apparent anthropogenic changes in PDO and NPGO decadal variability. This suggests that observed PDV responses to anthropogenic forcing may be erroneously convolved with the background trend pattern. Therefore, correctly determining the mean‐state trend is a necessary precursor for identifying possible forced changes to PDV.