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Indian summer monsoon (ISM) change under global warming is a serious concern because of its widespread socio‐economic impacts. Under the greenhouse gas (GHG)‐induced near future warming, climate models project a weakened ISM circulation, limiting the rate of monsoon rainfall increase. However, we find that climate models commonly simulate a strengthened ISM circulation in favor of ISM rainfall increase during the mid‐Pliocene that is often considered analogous to the ongoing anthropogenic warming. This enhanced ISM circulation change is physically consistent with a dramatically strong warming over Eastern Eurasia, which strengthened the mid‐upper tropospheric meridional temperature gradient across the ISM region. Sensitivity experiments reveal that such an Eastern Eurasian warming was closely associated with the northern continental greening via local vegetation‐albedo feedback. Our results highlight that the land cover changes, rather than GHG forcing, dominated this regional‐scale warming and resultant regional hydrological cycle in the mid‐Pliocene warm period.

Three new equilibrium mid‐Pliocene (MP) simulations are implemented with the Community Climate System Model version 4 (CCSM4) and Community Earth System Model versions 1.2 (CESM1.2) and 2 (CESM2). All simulations are carried out with the same boundary and forcing conditions following the protocol of Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). These simulations reveal amplified MP climate change relative to the preindustrial going from CCSM4 to CESM2, seen in global and polar averages of surface warming, sea ice reduction in both the Arctic and the Antarctic, and weakened Hadley circulation. The enhanced global mean warming arises from enhanced Earth system sensitivity (ESS) to not only CO2 change but also changes in boundary conditions primarily from vegetation and ice sheets. ESS is amplified by up to 70% in CCSM4 and up to 100% in CESM1.2 and CESM2 relative to the equilibrium climate sensitivity of respective models. Simulations disagree on several climate metrics. Different from CCSM4, both CESM1.2 and CESM2 show reduction of cloud cover, and weakened Walker circulation accompanied by an El Niño‐like mean state of the tropical Pacific in MP simulations relative to the preindustrial. This El Niño‐like mean state is consistent with paleo‐observational sea surface temperatures, suggesting an improvement upon CCSM4. The performances of MP simulations are assessed with a new compilation of observational MP sea surface temperature. The model‐data comparison suggests that CCSM4 is not sensitivity enough to the MP forcings, but CESM2 is likely too sensitive, especially in the tropics. Plain Language Summary Our knowledge of past climate evolves with both new paleo‐observations and advancements in modeling past climates. Using the mid‐Pliocene (MP, 3.205 million years ago) as an example, we demonstrate how to implement geological reconstructions of past topography, bathymetry, and vegetation distribution in Earth system models (ESMs); how to initialize these experiments; and, finally, the new knowledge learnt from simulations with three consecutive versions of the ESMs from the same model lineage. In our simulations, the MP climate warms substantially more than the estimated amount of warming that only consider changes in CO2 radiative forcing. The simulated MP climate features strongly amplified polar warmth, massive loss of Arctic and Antarctic summer sea ice, and weakened Northern Hemispheric cell of the Hadley circulation. Interestingly, two newer versions of ESMs are more sensitive to not only CO2 changes but also changes in biome range and ice sheets than the earlier version. Paleo‐observations suggest that MP global warming is underestimated by the previous versions of models but may be overestimated by the latest version. Key Points PlioMIP2 simulations are completed with Earth System Models from the NCAR family: CCSM4, CESM1, and CESM2 Simulated mid‐Pliocene climate by CESM2 features greater changes in many climate metrics than simulations by previous versions CESM1 and CESM2 match paleo‐observations better than CCSM4, yet CESM2 likely overestimates the Earth System Sensitivity

Given the threats that tropical cyclones (TC) pose to people and infrastructure, there is significant interest in how the climatology of these storms may change with climate. The global historical record has been extensively examined, but it is short and plagued with recurring questions about its homogeneity, limiting its effectiveness at assessing how TCs vary with climate. Past warm intervals provide an opportunity to quantify TC behavior in a warmer-than-present world. Here, we use a TC-resolving (∼25 km) global atmospheric model to investigate TC activity during the mid-Pliocene warm period (3.264–3.025 Ma) that shares similarities with projections of future climate. Two experiments, one driven by the reconstructed sea surface temperatures (SSTs) and the other by the SSTs from an ensemble of mid-Pliocene simulations, consistently predict enhanced global-average peak TC intensity during the mid-Pliocene coupled with longer duration, increased power dissipation, and a poleward migration of the location of peak intensity. The simulations are similar to global TC changes observed during recent global warming, as well as those of many future projections, providing a window into the potential TC activity that may be expected in a warmer world. Changes to power dissipation and TC frequency, especially in the Pacific, are sensitive to the different SST patterns, which could affect the viability of the role of TCs as a factor for maintaining a reduced zonal SST gradient during the Pliocene, as recently hypothesized.

In order to predict the fate of biodiversity in a rapidly changing world, we must first understand how species adapt to new environmental conditions. The long-term evolutionary dynamics of species' physiological tolerances to differing climatic regimes remain obscure. Here, we unite palaeontological and neontological data to analyse whether species' environmental tolerances remain stable across 3 Myr of profound climatic changes using 10 phylogenetically, ecologically and developmentally diverse mollusc species from the Atlantic and Gulf Coastal Plains, USA. We additionally investigate whether these species' upper and lower thermal tolerances are constrained across this interval. We find that these species' environmental preferences are stable across the duration of their lifetimes, even when faced with significant environmental perturbations. The results suggest that species will respond to current and future warming either by altering distributions to track suitable habitat or, if the pace of change is too rapid, by going extinct. Our findings also support methods that project species' present-day environmental requirements to future climatic landscapes to assess conservation risks.

The development of management strategies for the promotion of sustainable fisheries relies on a deep knowledge of ecological and evolutionary processes driving the diversification and genetic variation of marine organisms. Sustainability strategies are especially relevant for marine species such as the European sardine ( Sardina pilchardus ), a small pelagic fish with high ecological and socioeconomic importance, especially in Southern Europe, whose stock has declined since 2006, possibly due to environmental factors. Here, we generated sequences for 139 mitochondrial genomes from individuals from 19 different geographical locations across most of the species distribution range, which was used to assess genetic diversity, diversification history and genomic signatures of selection. Our data supported an extensive gene flow in European sardine. However, phylogenetic analyses of mitogenomes revealed diversification patterns related to climate shifts in the late Miocene and Pliocene that may indicate past divergence related to rapid demographic expansion. Tests of selection showed a significant signature of purifying selection, but positive selection was also detected in different sites and specific mitochondrial lineages. Our results showed that European sardine diversification has been strongly driven by climate shifts, and rapid changes in marine environmental conditions are likely to strongly affect the distribution and stock size of this species.

The evolution of Sahel summer rainfall in the context of global warming is a severe socio-economic concern because of its widespread influences on local agriculture, water resource management, food security, infrastructure planning, and ecosystems. Based on the mid-Pliocene simulations from the Pliocene Model Intercomparison Project Phase 2 and the historical simulations and shared socio-economic pathway 5–8.5 experiments from the Coupled Model Intercomparison Project phase 6, the present study contrasts the Sahel summer rainfall changes between the past mid-Pliocene and near future global warming climates. The results show that the Western African summer monsoon (WASM) circulation, closely linked with the Sahel summer rainfall change, tends to strengthen in both the past and future global warming climates, but the monsoonal circulation strengthening is much more intense in the past warm period than in the projected warm future. This causes that the multi-model ensemble (MME) mean increase ratio of Sahel summer rainfall in the past warming climate is about twice to three times larger than that in the future warming climate for the same increase of global mean surface temperature (the regional rainfall increase ratio in the MME mean: about 19.6% per one degree Celsius of global warming in the mid-Pliocene simulations versus about 7.7% per one degree Celsius of global warming in the SSP5-8.5 future projections). Such a striking discrepancy in the regional circulation and hydrological cycle changes is mainly attributed to a dramatically stronger warming over the Canadian Archipelago and Greenland during the mid-Pliocene warm period relative to the projected near future. The more significant northern high-latitude warming during the mid-Pliocene enhances the meridional temperature gradient between the extratropical and tropical regions, which could induce an excessive northward shift of the Intertropical Convergence Zone and a stronger WASM, and thus result in a more intense hydrological cycle around the Sahel region. Our results highlight that besides the global mean temperature increase, meridional warming patterns are also essential for the changes of WASM and regional hydrological cycle in a warmer world. Implications for projecting the regional monsoon and hydrological cycle changes at longer time scales than in the near future are discussed.

Ice-volume calibrations of the deep-ocean foraminiferal δ18O record imply orbitally influenced sea-level fluctuations of up to 30 m amplitude during the Mid-Pliocene, and up to 30 per cent loss of the present-day mass of the East Antarctic Ice Sheet (EAIS) assuming complete deglaciation of the West Antarctic Ice Sheet (WAIS) and Greenland. These sea-level oscillations have driven recurrent transgressions and regressions across the world's continental shelves. Wanganui Basin, New Zealand, contains the most complete shallow-marine Late Neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100 ka sea-level cycle since ca 3.6 Ma. This paper presents a synthesis of faunally derived palaeobathymetric data for shallow-marine sedimentary cycles corresponding to marine isotope stages M2-100 (ca 3.4-2.4 Ma). Our approach estimates the eustatic sea-level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation. The sea-level estimates are consistent with those from δ18O curves and numerical ice sheet models, and imply a significant sensitivity of the WAIS and the coastal margins of the EAIS to orbital oscillations in insolation during the Mid-Pliocene period of relative global warmth. Sea-level oscillations of 10-30 m were paced by obliquity.

Knowledge of dry–wet variations in arid Central Asia (ACA) during the mid-Pliocene warm period (mPWP; ~3.3–3.0 Ma) is instructive to understanding the future variations in this fragile ecosystem region. However, the dry–wet variations in ACA during the mPWP remain controversial. Here, we present high-resolution evaporite mineralogy records from the Gansen (GS) section of the western Qaidam Basin during 3.25–2.95 Ma. Based on the similar periodic variations between the calcite content and χfd/HIRM value-based precipitation records, we infer that the calcite content has the potential to reflect precipitation variations. The results suggest that the calcite content reveals dominant 20 kyr precessional cycles and strong 40 kyr non-obliquity cycles, consistent with the χfd/HIRM values from the GS section, further demonstrating that Qaidam precipitation was affected by the intensified East Asian summer monsoon during the mPWP. However, the occurrence of gypsum beds reveals that the Qaidam Basin still experienced relatively arid climatic conditions despite the increased precipitation during this warm interval. Furthermore, halite and gypsum records suggest that the degree of aridification was relatively moderate during 3.25–3.06 Ma but intensified during 3.06–2.95 Ma. For the intensified aridification, we infer that the further global cooling, which induced a relative decrease in water vapor, played an important role at ~3.06 Ma. Taking the mPWP as the reference, our findings indicate that under continued warming the East Asian summer monsoon will bring abundant water vapor to the inland basin and alleviate aridification in ACA. However, the increased precipitation will have difficulty reversing the aridification trend in the short term. This requires us to evaluate the warming and wetting trend in ACA from a dialectical perspective.

A comparative analysis of East Asian summer monsoon (EASM) precipitation is performed to reveal the drivers and mechanisms controlling the similarities of the mid-Pliocene EASM precipitation changes compared to the corresponding pre-industrial (PI) experiments derived from atmosphere-only (i.e. AGCM) and fully coupled (i.e. CGCM) simulations, as well as the large simulated differences in the mid-Pliocene EASM precipitation between the two simulations. The area-averaged precipitation over the EASM domain is enhanced in the mid-Pliocene compared to the corresponding PI experiments performed by both the AGCM (LMDZ5A) and the CGCM (IPSL-CM5A). Moisture budget analysis reveals that it is the surface warming over East Asia that drives the area-averaged EASM precipitation increase in the mid-Pliocene in both simulations. The surface warming increases the atmospheric moisture content, as revealed by an increase in the thermodynamic component of vertical moisture advection, resulting in enhanced mid-Pliocene EASM precipitation compared to PI in both simulations. Moist static energy diagnosis identifies the combined effect of enhanced zonal thermal contrast and column-integrated meridional stationary eddy velocity [Formula: see text] and its convergence [Formula: see text] as the physical mechanisms that sustain the enhancement of mid-Pliocene EASM precipitation in both simulations compared to the PI experiments. This takes place through a strengthening of the EASM circulation and moisture transport into the EASM domain associated with an increase in local moisture convergence in the mid-Pliocene in both simulations. Moisture budget analysis also reveals that the larger area-averaged mid-Pliocene EASM precipitation increase in the CGCM compared to its AGCM component is mainly caused by the dynamical component contributing more to the vertical moisture advection in the CGCM (i.e. IPSL-CM5A) compared to its AGCM (LMDZ5). The large simulated differences in the spatial pattern of the mid-Pliocene EASM precipitation between the two simulations result from the combined effect of enhanced meridional thermal contrast over the EASM domain and increased [Formula: see text] convergence over South China in the CGCM simulation compared to the AGCM simulation.

The Mid-Piacenzian Warm Interval (MPWI) is marked by warmer temperatures and higher atmospheric CO2 levels than today, making it an analogue for late-21st-century-warming, whereas the early Pleistocene cooling is more like today. We compare seasonal growth temperatures derived from oxygen isotope ratios (δ18O) and clumped isotopes (∆47) in Mercenaria. Modern shells were previously collected from coastal NC. The fossil shells are from the Duplin (MPWI) and Waccamaw Formations (early Pleistocene), NC. Oxygen isotope ratios range from −2.2‰ to 2.3‰ (modern), −0.9‰ to 2.4‰ (MPWI), and −0.9‰ to 2.9‰ (early Pleistocene). The values of Δ47 range from 0.576‰ to 0.639‰ (modern), 0.566‰ to 0.621‰ (MPWI), and 0.581‰ to 0.615‰ (early Pleistocene). We show that Mercenaria do not require a species-specific ∆47 calibration. Modern and MPWI ∆47-derived summer/winter temperatures (SST∆47) and seasonal amplitudes are indistinguishable from δ18O-derived temperatures. The early Pleistocene summer SST∆47 is indistinguishable from δ18O-derived temperatures, but the winter SST∆47 is warmer by 5 °C and may reflect within-shell time averaging. The modern summer/winter SST∆47 are indistinguishable from the MPWI, but the MPWI has a lower seasonal amplitude by 5 °C. Compared to our calculated δ18Osw values, modeled values for the MPWI are within error but are much lower, and they are not within error for the early Pleistocene.