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Abstract Climate mitigation strategies have been proposed to halt and potentially reverse global warming trends by the mid-twenty-first century. Previous studies have shown different aspects of climate irreversibility at regional or global scales, but the roles of clouds and atmospheric radiation remain elusive. Using the fully coupled NCAR Community Earth System Model, version 2 (CESM2), we examine climate reversibility in a scenario where the atmospheric carbon dioxide (CO₂) concentration gradually increases starting in 2015 (∼400 ppm) until 2075 (∼800 ppm) and then decreases back to the 2015 level. We find that the lowest reversibility of surface temperature occurs in the Southern Hemisphere mid–high latitudes. In addition to the slow ocean response, profound cloud–radiation feedbacks are identified in this study, which contribute to regional temperature irreversibility. Cloud properties and radiative effects show the lowest reversibility over 30°–45° and 60°–75°S. The strong inertia of the Southern Ocean circulations and the Atlantic meridional overturning circulation (AMOC) jointly induce hemispheric surface temperature asymmetry on a 60-yr time scale, leading to a southward shift of the Hadley cell with a narrowed subsidence branch and a persistent moisture divergence over 30°–45°S during the removal of CO₂. The resultant humidity reduction decreases low-level cloud fraction and liquid water path, contributing to anomalous shortwave radiation that suppresses local temperature recovery. Moreover, subpolar clouds in the Southern Hemisphere are closely connected with Antarctic sea ice which exhibits substantial irreversibility following the Southern Ocean circulation responses. Our findings demonstrate that coupled ocean–atmosphere processes involving cloud and radiation feedbacks collectively determine climate reversibility and shape regional climate change patterns. 

Abstract Repressing transposable elements via piRNAs represents a critical defense mechanism for germ cells to maintain genomic integrity. The primary piRNA biogenesis largely occurs at intermitochondrial cement (IMC), which is characterized by uniquely clustered mitochondria and ribonucleoproteins as “cementing material.” RNA-binding proteins at IMC, such as MILI, are essential for piRNA biogenesis. However, MILI proteins do not possess mitochondrial localization signals; thus, they must rely on other proteins to functionally communicate with IMC. In this study, we identified GASZ as a crucial interacting partner for MILI at IMC from prospermatogonia to spermatocytes. We found that GASZ proteins at mitochondria directly recruited MILI to IMC for piRNA biogenesis. Abolishing GASZ–MILI interaction in the embryonic germ cells reduced fetal piRNA level, increased transposon expression, and compromised spermatogonial and spermatocyte development during the first wave of spermatogenesis. In addition, disrupting GASZ–MILI interaction in adulthood significantly impaired spermatogenesis, with reduced spermatocyte and spermatid formation, proving that MILI and GASZ partner together to regulate steady-state spermatogenesis. Taken together, by revealing critical GASZ–MILI interaction at IMC and defining its impact on spermatogenesis, our findings critically inform how the piRNA biogenesis machinery is constructed via protein interactions to preserve germline DNA integrity for proper germ cell development. 

In spring, global warming exhibits prominent zonal asymmetry at continental scales, with Eurasia warming three times faster than North America during 1979–2021. Meanwhile, snow loss is also highly asymmetric. These changes are critical for regional agriculture and water management, yet the roles of specific forcings behind them remain unclear. Based on hierarchical large-ensemble climate model simulations, ~32 ± 28% of the surface air temperature (SAT) asymmetric trend and 16 ± 13% of the snow cover asymmetric trend between Eurasia and North America are attributable to tropical Pacific variability. Single-forcing experiments reveal that anthropogenic aerosols can induce a comparable asymmetry, accounting for 34 ± 23% (24 ± 17%) of observed SAT (snow cover) asymmetric trends. However, their effects are largely masked by the greenhouse gas forcing. As anthropogenic aerosol emissions are expected to decline, the current warming asymmetry may reverse in the future. 

Abstract Silencing evolutionary young retrotransposons by cytosine DNA methylation is essential for spermatogenesis, as failure to methylate their promoters leads to reactivation, meiotic failure, and infertility. How retrotransposons reactivate in the absence of DNA methylation is poorly understood. We show that upon defective DNA methylation, distinct retrotransposon families display unique expression patterns and chromatin landscapes during mouse spermatogenesis. We find that their reactivation in meiotic spermatocytes correlates with the loss of bivalent H3K4me3-H3K27me3 chromatin marks. Through proteomics and chromatin profiling, we identify NRF1 as a DNA methylation-sensitive transcription factor that transactivates unmethylated retrotransposons. Conditional germline knockout ofNrf1in the absence of DNA methylation rescues the silencing of the most mutagenic retrotransposon in mice, namely Intracisternal A-particle or IAP. Our findings reveal that chromatin modifications together with a DNA methylation-sensitive transcription factor regulate retrotransposon expression in the absence of DNA methylation in spermatogenesis, revealing a mechanism by which retrotransposons proliferate in the germline after evading DNA methylation-based silencing. 

Abstract The export of the North Atlantic Deep Water (NADW) from the subpolar North Atlantic is known to affect the variability in the lower limb of the Atlantic meridional overturning circulation (AMOC). However, the respective impact from the transport in the upper NADW (UNADW) and lower NADW (LNADW) layers, and from the various transport branches through the boundary and interior flows, on the subpolar overturning variability remains elusive. To address this, the spatiotemporal characteristics of the circulation of NADW throughout the eastern subpolar basins are examined, mainly based on the 2014–20 observations from the transatlantic Overturning in the Subpolar North Atlantic Program (OSNAP) array. It reveals that the time-mean transport within the overturning’s lower limb across the eastern subpolar gyre [−13.0 ± 0.5 Sv (1 Sv ≡ 10⁶m³s⁻¹)] mostly occurs in the LNADW layer (−9.4 Sv or 72% of the mean), while the lower limb variability is mainly concentrated in the UNADW layer (57% of the total variance). This analysis further demonstrates a dominant role in the lower limb variability by coherent intraseasonal changes across the region that result from a basinwide barotropic response to changing wind fields. By comparison, there is just a weak seasonal cycle in the flows along the western boundary of the basins, in response to the surface buoyancy-induced water mass transformation. 

Tropical cyclone rainfall (TCR) extensively affects coastal communities, primarily through inland flooding. The impact of global climate changes on TCR is complex and debatable. This study uses an XGBoost machine learning model with 19-year meteorological data and hourly satellite precipitation observations to predict TCR for individual storms. The model identifies dust optical depth (DOD) as a key predictor that enhances performance evidently. The model also uncovers a nonlinear and boomerang-shape relationship between Saharan dust and TCR, with a TCR peak at 0.06 DOD and a sharp decrease thereafter. This indicates a shift from microphysical enhancement to radiative suppression at high dust concentrations. The model also highlights meaningful correlations between TCR and meteorological factors like sea surface temperature and equivalent potential temperature near storm cores. These findings illustrate the effectiveness of machine learning in predicting TCR and understanding its driving factors and physical mechanisms. 

Abstract Mitochondrial features and activities vary in a cell type- and developmental stage-dependent manner to critically impact cell function and lineage development. Particularly in male germ cells, mitochondria are uniquely clustered into intermitochondrial cement (IMC), an electron-dense granule in the cytoplasm to support proper spermatogenesis. But it remains puzzling how mitochondria assemble into such a stable structure as IMC without limiting membrane during development. Here, we showed that GASZ (germ cell-specific, ankyrin repeat, SAM and basic leucine zipper domain containing protein), a mitochondrion-localized germ cell-specific protein, self-interacted with each other to cluster mitochondria and maintain protein stability for IMC assembling. When the self-interaction of GASZ was disrupted by either deleting its critical interaction motif or using a blocking peptide, the IMC structure was destabilized, which in turn led to impaired spermatogenesis. Notably, the blocked spermatogenesis was reversible once GASZ self-interaction was recovered. Our findings thus reveal a critical mechanism by which mitochondrion-based granules are properly assembled to support germ cell development while providing an alternative strategy for developing nonhormonal male contraceptives by targeting IMC protein interactions. 

Abstract Saharan dust exerts profound impacts on the genesis and intensification of tropical cyclones (TCs). Such impacts on various stages of the TCs have yet to be explored. In this study, we utilize the Cloud‐Resolving weather research and forecasting model (WRF) to investigate the relative importance of the microphysical and radiative effects of dust on two hurricanes (Earl and Danielle) at different life stages under similar dynamical conditions in 2010. Both TCs were embedded in a dusty environment throughout their lifetime. A new dust ice nucleation scheme was implemented into the aerosol‐aware Texas A&M University two‐moment microphysical scheme in WRF. Moreover, the dust radiative effect was included in the Goddard Shortwave Scheme of WRF. Our sensitivity experiments show that the radiative effect of dust (DRAD) amplified the mid‐level ridge in the Central Atlantic Ocean through temperature perturbation, changing the tracks of Danielle and Earl. Further analyses reveal an early shift of Danielle's maximum intensity for 12 hours but a significantly suppressed Earl in DRAD. In addition, the microphysical effect of dust had little impact on the large‐scale dynamical fields and storm tracks. The inclusion of dust as ice nucleation particles results in more variations in the intensity of Danielle and Earl than in other scenarios. This is owing to the higher maximum diabatic heating rate in the rainband region that perturbs the size of the TC. This study shows the dominant dust radiative effects on both intensity and track of the storm. In addition, there is evidence that dust suppresses the early stage TC but provides favorable conditions for matured TC. Both findings have profound implications for hurricane forecast and address the importance of accounting for detailed cloud microphysics and aerosol‐TC interactions in the operational forecasting models. 

Aerosols can affect photosynthesis through radiative perturbations such as scattering and absorbing solar radiation. This biophysical impact has been widely studied using field measurements, but the sign and magnitude at continental scales remain uncertain. Solar-induced fluorescence (SIF), emitted by chlorophyll, strongly correlates with photosynthesis. With recent advancements in Earth observation satellites, we leverage SIF observations from the Tropospheric Monitoring Instrument (TROPOMI) with unprecedented spatial resolution and near-daily global coverage, to investigate the impact of aerosols on photosynthesis. Our analysis reveals that on weekends when there is more plant-available sunlight due to less particulate pollution, 64% of regions across Europe show increased SIF, indicating more photosynthesis. Moreover, we find a widespread negative relationship between SIF and aerosol loading across Europe. This suggests the possible reduction in photosynthesis as aerosol levels increase, particularly in ecosystems limited by light availability. By considering two plausible scenarios of improved air quality—reducing aerosol levels to the weekly minimum 3-d values and levels observed during the COVID-19 period—we estimate a potential of 41 to 50 Mt net additional annual CO₂uptake by terrestrial ecosystems in Europe. This work assesses human impacts on photosynthesis via aerosol pollution at continental scales using satellite observations. Our results highlight i) the use of spatiotemporal variations in satellite SIF to estimate the human impacts on photosynthesis and ii) the potential of reducing particulate pollution to enhance ecosystem productivity.