Climate Forcing Research Articles

Promising Regions for Detecting the Overturning Circulation in Atlantic 231Pa/230Th: A Model‐Data Comparison

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is a critical component of the climate system, strongly influencing the climate via ocean heat transport. The AMOC is thought to have had different characteristics during glacial periods and is expected to change under anthropogenic climate forcing. To reconstruct past AMOC strength, the 231Pa/230Th (protactinium‐231 to thorium‐230) ratio measured in marine sediments serves as an often used proxy. However, this ratio reflects not only circulation changes, but also effects from biological particle export and benthic nepheloid layers. Therefore, it remains an open question which regions exhibit a reliable AMOC signal in their sedimentary 231Pa/230Th. We utilize the Bern3D model and a compilation of sediment 231Pa/230Th records, including records from 11 new core locations. This study suggests that equatorial West Atlantic 231Pa/230Th is as suitable as the Bermuda Rise region to detect AMOC changes. The 231Pa/230Th response to AMOC changes observed in part of the northern North Atlantic (which is opposite to regions further south) is caused mainly by AMOC‐induced changes in particle production. Cores in this region are promising to reconstruct AMOC strength, despite exhibiting an AMOC‐to‐231Pa/230Th relationship opposite from usual and high opal levels. Additional cores in the North Atlantic at 40°–60°N between 1 and 2 km depth are desirable for the application of 231Pa/230Th. Our results suggest a new focus of 231Pa/230Th reconstructions on the equatorial West Atlantic and the northern North Atlantic, which appear to be best suited to quantify past AMOC strength.

Sediment fluxes dominate glacial–interglacial changes in ocean carbon inventory: results from factorial simulations over the past 780 000 years

Abstract. Atmospheric CO2 concentrations varied over ice age cycles due to net exchange fluxes of carbon between land, ocean, marine sediments, lithosphere, and the atmosphere. Marine sediments and polar ice cores archived indirect biogeochemical evidence of these carbon transfers, which resulted from poorly understood responses of the various carbon reservoirs to climate forcing. Modelling studies demonstrated the potential of several physical and biogeochemical processes to impact atmospheric CO2 under steady-state glacial conditions. However, it remains unclear how much these processes affected carbon cycling during transient changes of repeated glacial cycles and what role the burial and release of sedimentary organic and inorganic carbon and nutrients played. Addressing this knowledge gap, we produced a simulation ensemble with various idealised physical and biogeochemical carbon cycle forcings over the repeated glacial inceptions and terminations of the last 780 kyr with the Bern3D Earth system model of intermediate complexity, which includes dynamic marine sediments. The long simulations demonstrate that initiating transient glacial simulations with an interglacial geologic carbon cycle balance causes isotopic drifts that require several hundreds of thousands of years to overcome. These model drifts need to be considered when designing spin-up strategies for model experiments. Beyond this, our simulation ensemble allows us to gain a process-based understanding of the transient carbon fluxes resulting from the forcings and the associated isotopic shifts that could serve as proxy data. We present results of the simulated Earth system dynamics in the non-equilibrium glacial cycles and a comparison with multiple proxy time series. From this we draw several conclusions. In our simulations, the forcings cause sedimentary perturbations that have large effects on marine and atmospheric carbon storage and carbon isotopes. Dissolved inorganic carbon (DIC) changes differ by a factor of up to 28 between simulations with and without interactive sediments, while CO2 changes in the atmosphere are up to 4 times larger when interactive sediments are simulated. The relationship between simulated DIC (−1800–1400 GtC) and atmospheric CO2 change (−170–190 GtC) over the last deglaciation is strongly setup-dependent, highlighting the need for considering multiple carbon reservoirs and multi-proxy analyses to more robustly quantify global carbon cycle changes during glacial cycles.

Underestimated Ural blocking events lead to weakened spring Arctic warming in CMIP6 simulations

Historical Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations underestimate spring Arctic warming due to insufficient representation of Ural blocking events. Observations reveal that strong winter warming over the Barents–Kara Sea (BKS) reduces the meridional potential vorticity gradient, thereby enhancing atmospheric blocking events and driving Arctic surface warming in spring. Many CMIP6 members, which exhibit lower sensitivity to climate forcing, involve the use of initial fields with warmer climate conditions (e.g. reduced sea ice cover). Consequently, these models simulate less sea ice melting and minimal winter BKS warming, leading to weaker Ural blocking events and underestimation of spring Arctic surface warming. While recent global surface temperature trends among CMIP6 models are relatively consistent, their future projections diverge due to their varying climate sensitivities, potentially underestimating global warming across different scenarios.

Longer Lifetime of BC from Fossil Fuel Combustion than from Biomass Burning: Δ14C Evidence.

Black carbon (BC) significantly contributes to atmospheric warming and glacier melting. However, the atmospheric lifetime of BC from different fuel sources remains poorly constrained. By analyzing Δ14C of BC in PM2.5 and precipitation samples collected for three years at a remote site in the Tibetan Plateau, we found that BC from fossil fuel contribution (ffossil BC) in PM2.5 exhibited greater seasonal variation than those from South Asia and emission inventories. Precipitation-induced fractionation between fossil fuel combustion-derived BC (BCff) and biomass burning-derived BC (BCbb) resulted in an increase of ffossil BC to 68 ± 7% during the wet monsoon season, which is significantly higher than levels measured at a background site in South Asia and in simultaneously collected precipitation samples. Our findings provide direct evidence that the lifetime of BCff is longer than that of BCbb during the monsoon season. These results emphasize the increased climate forcing of BCff relative to BCbb at remote sites receiving long-range transported BC.

Black Carbon: Its Sources, Environment and Health Impacts & Mitigation Solutions for Sustainable Development

Black carbon (BC), in spite of being a short-lived climate pollutant (SLCP), with life time of only few days, is found to be a powerful climate forcer that has hundreds to thousand times more potential of warming the atmosphere than carbon dioxide. It severely affects climate, cryosphere, human health, ecosystems and agricultural productivity. BC is a formed by the incomplete combustion of fossil fuels, wood and other fuels. Household cooking methods are the major contributor of the global carbon emissions, followed by transport, industrial and agriculture sectors. Wild fires also contribute to BC emission. BC absorbs the incoming solar radiation which heats the atmosphere, affecting the cloud formation and rainfall in the region. which is critical for agriculture, affecting human livelihoods in addition to ecosystem. This, in turn, affects the economy. Its deposition on ice/snow, reduces its surface albedo that increases the absorption of sunlight, in turn, faster melting of ice/glaciers and rise in sea level. The Arctic and glaciated regions of Himalayas are under high risk. Being small enough in size, black carbon can be inhaled, contributing to respiratory and cardiovascular diseases leading to lung cancer and even to birth defects. Coordinated efforts would be required for attaining zero carbon emission for sustainable development, a goal set by UNEP. This paper presents a review on the various sources of black carbon, its effects on environment, health and economy. The steps to be taken to reduce the black carbon level for sustainable development are also reviewed.

A Holistic View of Climate Sensitivity

The notion of climate sensitivity has become synonymous with equilibrium climate sensitivity (ECS), or the equilibrium response of the Earth system to a doubling of CO2. But there is a hierarchy of measures of climate sensitivity, which can be arranged in order of increasing complexity and societal relevance and which mirror the historical development of climate modeling. Elements of this hierarchy include the well-known ECS and transient climate response and the lesser-known transient climate response to cumulative emissions and zero emissions commitment. This article describes this hierarchy of climate sensitivities and associated modeling approaches. Key concepts reviewed along the way include climate forcing and feedback, ocean heat uptake, and the airborne fraction of cumulative emissions. We employ simplified theoretical models throughout to encapsulate well-understood aspects of these quantities and to highlight gaps in our understanding and areas for future progress. ▪ There is a hierarchy of measures of climate sensitivity, which exhibit a range of complexity and societal relevance. ▪ Equilibrium climate sensitivity is only one these measures, and our understanding of it may have reached a plateau. ▪ The more complex measures introduce new quantities, such as ocean heat uptake efficiency and airborne fraction, which deserve increased attention.

Environment-driven trends in larval abundance predict fishery recruitment in two saltwater basses

Abstract Environmental and biological factors influencing fish larvae can drive fishery cohort strength, yet larval abundance is typically a better indicator of spawning biomass. Under a changing ocean, studies that explore the relationships between environmental variables, larval abundance, and fishery recruitment remain valuable areas for ongoing research. We focus on a popular, recreational-only, multispecies saltwater bass fishery (genus Paralabrax) whose population status and recovery potential are uncertain. We resolved Paralabrax spp. larval data to species over a 54-year period (1963–2016) and used species distribution models to (i) generate and test species-specific standardized indices of larval abundance as indicators of adult stock status and fishery recruitment and (ii) evaluate long-term spatiotemporal trends in their population dynamics relative to environmental variables and climate forcing. Contrary to initial hypotheses, species-specific larval abundance predicted future catches, with higher recent larval abundances suggesting potential for fishery recovery. Temperature, zooplankton biomass, and isothermal depth were important predictors of bass larval abundance, indicating these variables could also be valuable for predicting fishery recruitment and anticipating population change. Our findings paint a path forward towards a more ecosystem-based fishery management approach for this important fishery and may serve as a template for data- or assessment-limited fisheries.

Impacts of Changing Temperatures on the Water Budget in the Great Salt Lake Basin

Quantifying the water budget in the Great Salt Lake (GSL) basin is a nontrivial task, especially under a changing climate that contributes to increasing temperatures and a shift towards more rainfall and less snowfall. This study examines the potential impacts of temperature thresholds on the water budget in the GSL, emphasizing the influence on snowmelt, evapotranspiration (ET), and runoff under varying climate warming scenarios. Current hydrological models such as the Variable Infiltration Capacity (VIC) model use a universal temperature threshold to partition snowfall and rainfall across different regions. Previous studies have argued that there is a wide range of thresholds for partitioning rainfall and snowfall across the globe. However, there is a clear knowledge gap in quantifying water budget components in the Great Salt Lake (GSL) basin corresponding to varying temperature thresholds for separating rainfall and snowfall under the present and future climates. To address this gap, the study applied temperature thresholds derived from observation-based data available from National Center for Environmental Prediction (NCEP) to the VIC model. We also performed a suite of hydrological experiments to quantify the water budget of the Great Salt Lake basin by perturbing temperature thresholds and climate forcing. The results indicate that higher temperature thresholds contribute to earlier snowmelt, reduced snowpack, and lower peak runoff values in the early spring that are likely due to increased ET before peak runoff periods. The results show that the GSL undergoes higher snow water equivalent (SWE) values during cold seasons due to snow accumulation and lower values during warm seasons as increased temperatures intensify ET. Projected climate warming may result in further reductions in SWE (~71%), increased atmospheric water demand, and significant impacts on water availability (i.e., runoff reduced by ~20%) in the GSL basin. These findings underscore the potential challenges that rising temperatures pose to regional water availability.

Impact of Paleocene–Eocene tectonic and climatic forcing on Arctic sediment transfer variability: SW Barents Sea, Norway

During the Paleocene and Eocene, many Arctic basins experienced multiple, yet synchronous periods of increased sedimentation rates. Several causal factors have been suggested including major volcanic events, tectonic plate reorganization and plate break-up, as well as widespread uplift along with contemporaneous and short-lived hyperthermal events. However, the significance of and relation between tectonic and climatic forcing on Arctic sediment transfer during the early Paleogene is poorly understood. In this case study from the Barents Shelf margin in the Norwegian Arctic, we present previously unpublished cores combined with exploration wells, and new high-resolution 3D seismic data to investigate sedimentary stacking patterns and geomorphological features in the Sørvestsnaget Basin. Our integrated investigations reveal the development of climate-controlled and tectonically-driven submarine fans. The PETM fans display an individual fan as a result of single depositional event compared to the middle Eocene fans that show stacked submarine fans probably deposited during multi-phase events. Our Stratigraphic Forward Modelling analysis indicates that regional-scale tectonically induced uplift significantly increased the amount of sand delivered to the basin as documented by a thickening of the basin fill succession. The climatic component contributes to sand transport variability to the basin, and thus the temporal evolution pattern of sand is much varied. Finally, we discuss our findings with the tectonic and climatic forcing factors in a circum-Arctic perspective.

Orbital Scale Kuroshio Current Variations of the Northwestern Pacific Ocean in the Early Pleistocene (Marine Isotope Stage 40–36) Based on Calcareous Nannofossil Records

AbstractThe Quaternary period was marked by distinct glacial‐interglacial climate cycles driven by orbital forcing, which are closely linked to marine environmental change. In the northwestern Pacific Ocean, the subtropical Kuroshio Current and subarctic Oyashio Current play crucial roles in global climate modulation. Despite their significance, paleoceanographic studies with high temporal resolutions are scarce. Here, we investigated calcareous nannofossil assemblages of the Kazusa Group to reconstruct the sea‐surface conditions around the Japanese Archipelago during the marine isotope stage (MIS) 40–36, providing an important climatic record prior to the mid‐Pleistocene transition. A time‐series analysis of nannofossil floral changes revealed orbital scale Kuroshio Current variability as well as Kuroshio Front migrations, suggesting that the Kuroshio Current variations were linked to the variability of the North Pacific subtropical gyre. Moreover, orbital‐scale southward migrations of the Kuroshio Front during the glacial periods may be correlated with the displacement of the intertropical convergence zone caused by the northern hemisphere climate changes. Finally, spectral and wavelet analyses of calcareous nannofossil abundance showed a periodicity of ∼20 Kyr, indicating that these variabilities in the Kuroshio Current are predominantly controlled by high‐latitude climate forcings. Therefore, the results obtained in this study suggest that Kuroshio Current variations are related to climatic changes from low to high latitudes during the MIS 40–36.

Potential Spatial Mismatches Between Marine Predators and Their Prey in the Southern Hemisphere in Response to Climate Change.

Global change is rapidly reshaping species' habitat suitability ranges, hence leading to significant shifts in the distribution of marine life. Contrasting distributional responses among species can alter the spatial overlap between predators and prey, potentially disrupting trophic interactions and affecting food web dynamics. Here, we evaluate long-term changes in the spatial overlap of habitat suitability ranges for trophically related species, including crustaceans, fish, penguins, and pinnipeds across 12 Large Marine Ecosystems from the Southern Hemisphere, merged into three primary regions: South America, Southern Africa, Australia and New Zealand. To this aim, we first use Boosted Regression Trees (BRTs) to hindcast and project species-specific changes in suitable habitat from 1850 to 2100 under two future climate scenarios: SSP1-2.6 (low climate forcing) and SSP5-8.5 (high climate forcing). We then analyze changes in species habitat suitability and potential predator-prey spatial overlaps. Findings reveal that marine species generally exhibit changes in their suitable habitats, with pronounced shifts towards higher latitudes under the SSP5-8.5 scenario. However, contrasting trends emerge among predators across functional groups and regions of South America, Southern Africa, Australia and New Zealand. These variations highlight the need for species and regional-specific management responses. We also project contrasting spatial mismatches between predators and prey: predators experiencing declines in suitable habitat tend to exhibit greater overlap with their prey in future scenarios, whereas those with expanding suitable habitat show reduced spatial overlap with their prey. This study provides valuable insights that can inform spatial management strategies in response to climate change and illustrate how climate change may weaken species' ability to adapt to climate-driven environmental changes due to trophic disruptions.

Evidence for Poleward Migration of the Asian Monsoon During the Paleocene‐Eocene Thermal Maximum

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM, ∼56 Ma), was a transient episode of global warming, and caused profound changes in biology and climate. The evolution of the hydroclimate during the PETM in East Asia, which currently is influenced by the Asian Monsoon and hosts ∼20% of the world's population, is crucial to understand the future monsoon and climate changes. However, PETM records in Asia are relatively rare and it remains poorly understood how the hydroclimate responded to climate forcing under extreme atmosphere pCO2. Here we present stable carbon isotope records of bulk carbonate and total organic carbon (δ13Ccarb and δ13CTOC) from lacustrine deposits in the Jianghan Basin, Central China that both record the global carbon isotope excursion (CIE) that marks the PETM. The magnitude of both the CIEs in δ13Ccarb and δ13CTOC are larger than that presumed in the global exogenic carbon pool, as is common for terrestrial and marginal marine records. The particularly large amplitude (∼11.4‰) and unique shape of CIE in δ13Ccarb, which represents authigenic lacustrine carbonates and therefore lake dissolved inorganic carbon δ13C values. Although our evidence against diagenesis is not fully conclusive, this signal implies the local addition of 13C‐depleted carbon in excess of the global input. We consider increased transport rates of organic matter‐derived carbon from the catchment to the lake the most likely source. Combined with the disappearance of evaporitic deposits during the PETM, we attribute this to an increase in precipitation and erosion, possibly linked to a northward extension of the Asian summer monsoon.

Multiple Climate Forcings Decomposed From a Tibetan Plateau Ice Core Isotope Record

AbstractDue to the impact of various climate systems, including the Asian Summer Monsoon (ASM) and westerlies, it is challenging to identify specific climate variables from the ice core δ18O records of the Tibetan Plateau (TP). Here, we disentangle the major climate modes by applying the singular spectrum analysis method to a δ18O time series in a shallow ice core retrieved from central TP. This method allows us to identify three major climate modes: the trend component, the El Niño Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). The trend component mainly reflects warming in the middle and upper troposphere over the south of the TP rather than the low land surface temperature changes. Furthermore, we found that water vapor δ18O in these upper atmospheric layers positively correlates with temperature. We propose that the up‐and‐over transport of such water vapor to the TP contributes to the temperature signal in the ice core δ18O record, which also helps understand the increasing trend in TP ice core δ18O records during the last deglaciation. ENSO and PDO affect the intensity of the ASM through two phases: warm phases tend to weaken the monsoon, leading to higher δ18O values, whereas cool phases strengthen the monsoon, resulting in lower δ18O values. Our findings suggest that multiple climate forcings can have their specific isotopic imprints in isotopic archives and highlight the importance of analyzing the integrated effects of diverse climatic drivers. The analyses also shed light on separating different climate signals from paleoclimate records.

Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing

Abstract. The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events. While growing geological evidence has demonstrated a temporal correlation between astronomical forcing and anoxia during this period, underlying physical mechanisms remain unknown, hence questioning causality. Here, we perform multiple sensitivity experiments, using an Earth system model of intermediate complexity (cGENIE), to isolate the influences of specific Devonian climate and palaeogeography components on ocean oxygen levels, contributing to the better understanding of the intricate interplay of factors preconditioning the ocean to anoxia. We quantify the impact of continental configuration, ocean–atmosphere biogeochemistry (global mean oceanic PO4 concentration and atmospheric pO2), climatic forcing (pCO2), and astronomical forcing on background oceanic circulation and oxygenation during the Devonian. Our results indicate that continental configuration is crucial for Devonian ocean anoxia, significantly influencing ocean circulation and oxygen levels while consistently modulating the effects of other Devonian climate components such as oceanic PO4 concentration, atmospheric pO2 and pCO2, and orbital forcing. The evolution of continental configuration provides a plausible explanation for the increased frequency of ocean anoxic events identified during the Middle and Late Devonian periods, as it contributed to the expansion of oxygen-depleted zones. Our simulations also show that both the decreased atmospheric pO2 and increased oceanic PO4 concentration exacerbate ocean anoxia, consistent with established knowledge. The variation of pCO2 reveals a wide range of ocean dynamics patterns, including stable oscillations, multiple convection cells, multistability, and hysteresis, all leading to significant variations of the ocean oxygen levels and therefore strongly impacting the preconditioning of the ocean to anoxia. Furthermore, multistability and important hysteresis (particularly slow ocean time response) offer different mechanisms to account for the prolonged duration of some ocean anoxic events. Finally, we found that astronomical forcing substantially impacts ocean anoxia by altering ocean circulation and oxygen solubility, with obliquity consistently emerging as the primary orbital parameter driving ocean oxygen variations.

Slowed Response of Atlantic Meridional Overturning Circulation Not a Robust Signal of Collapse

AbstractUsing an idealized model of the Atlantic meridional overturning circulation (AMOC), we test whether changes in the statistical properties of an AMOC time series can reveal Critical Slowing Down (CSD) and serve as early warnings of an upcoming critical transition. We calculate CSD indicators for simulations across varying parameter regimes, investigating the system's steady‐state dynamical structure and its evolution under gradual climate forcing. We find that the modeled AMOC features bistability for relatively weak gyre salinity exchange, but no bistability when the gyres are sufficiently strong. However, CSD indicators consistently warn of a collapse across the gyre strength parameter space, even when no bifurcations occur, thus raising false alarms. We argue that CSD should be applied cautiously in systems where the dynamical structure and physical response to forcing are not fully known (such as the AMOC), specifically where it is not a priori clear whether the system is in a multistable regime.

Forecasting contrail climate forcing for flight planning and air traffic management applications: the CocipGrid model in pycontrails 0.51.0

Abstract. The global annual mean contrail climate forcing may exceed that of aviation's cumulative CO2 emissions. As only 2 %–3 % of all flights are likely responsible for 80 % of the global annual contrail energy forcing (EFcontrail), re-routing these flights could reduce the occurrence of strongly warming contrails. Here, we develop a contrail forecasting tool that produces global maps of persistent contrail formation and their EFcontrail formatted to align with standard weather and turbulence forecasts for integration into existing flight planning and air traffic management workflows. This is achieved by extending the existing trajectory-based contrail cirrus prediction model (CoCiP), which simulates contrails formed along flight paths, to a grid-based approach that initializes an infinitesimal contrail segment at each point in a 4D spatiotemporal grid and tracks them until their end of life. Outputs are provided for N aircraft-engine groups, with groupings based on similarities in aircraft mass and engine particle number emissions: N=7 results in a 3 % mean error between the trajectory- and grid-based CoCiP, while N=3 facilitates operational simplicity but increases the mean error to 13 %. We use the grid-based CoCiP to simulate contrails globally using 2019 meteorology and compare its forecast patterns with those from previous studies. Two approaches are proposed to apply these forecasts for contrail mitigation: (i) monetizing EFcontrail and including it as an additional cost parameter within a flight trajectory optimizer or (ii) constructing polygons to avoid airspace volumes with strongly warming contrails. We also demonstrate a probabilistic formulation of the grid-based CoCiP by running it with ensemble meteorology and excluding grid cells with significant uncertainties in the simulated EFcontrail. This study establishes a working standard for incorporating contrail mitigation into flight management protocols and demonstrates how forecasting uncertainty can be incorporated to minimize unintended consequences associated with increased CO2 emissions from re-routes.

Current and future adaptation potential of heat-tolerant maize in Cameroon: a combined attribution and adaptation study

Abstract Sub-Saharan Africa is projected to be exposed to substantial climate change hazards, especially in its agricultural sector, so adaptation will be necessary to safeguard crop yields. Tropical and subtropical maize production regions approach critical temperature thresholds in the growing season already in today’s climate, and climate change might already be contributing to this. In this study we analyse the impact of anthropogenic climate change on maize yields and the potential for adaptation in Cameroon. We innovate by introducing a counterfactual climate as baseline to a definition for adaptation potential proposed in the literature to assess the relative benefit heat-tolerant crop varieties have already under current and under projected climate change. Spatially detailed simulations of maize yields are performed using the process-based crop model APSIM with W5E5 reanalysis data and bias-corrected and downscaled climate model data from CMIP6/ISIMIP3b for counterfactual, historical and projected future climate scenarios SSP1-2.6 and SSP3-7.0. It is found that unadapted maize yields experience significant losses under all climate change scenarios, with mean losses of 0.3 t/ha for the current period compared to the counterfactual climate without anthropogenic climate forcings and that yields are significantly higher for the heat-tolerant varieties across all scenarios simulated. Yield impacts of heat tolerance are highest under projected climate change, making it effective climate change adaptation. This result is robust to the exact value of parameterised heat tolerance. Breeding heat-tolerant varieties as parametrised in this study can be an effective adaptation but is still not enough to mitigate simulated losses under a high-emissions scenario.

Climate and Human Evolution: Insights from Marine Records.

The relationship between climate and human evolution is complex, and the causal mechanisms remain unknown. Here, we review and synthesize what is currently known about climate forcings on African landscapes, focusing mainly on the last 4 million years. We use information derived from marine sediment archives and data-numerical climate model comparisons and integration. There exists a heterogeneity in pan-African hydroclimate changes, forced by a combination of orbitally paced, low-latitude fluctuations in insolation; polar ice volume changes; tropical sea surface temperature gradients linked to the Walker circulation; and possibly greenhouse gases. Pan-African vegetation changes do not follow the same pattern, which is suggestive of additional influences, such as CO2 and temperature. We caution against reliance on temporal correlations between global or regional climate, environmental changes, and human evolution and briefly proffer some ideas on how pan-African climate trends could help create novel conceptual frameworks to determine the causal mechanisms of associations between climate/habitat change and hominin evolution.

Channel Incising and Sandbar Growth in the Upper Yangtze River Estuary During 1994–2019, China

Anthropogenic activities and climate change have increased the stress on the world’s estuaries over the past decades. Limited knowledge exists about how estuarine receding responds to human interference, particularly the geomorphic dynamics of channels and sandbars. Here, we evaluate the topographic evolution of the upper Yangtze River Estuary (YRE), the largest branch reach with frequently shifting sandbars, from 1994 to 2019. Our results show that a net channel erosion of 9.59 × 108 m3 occurred in the upper YRE, equivalent to an annual erosion depth of 8.67 cm. On the contrary, sandbars with a large area increased from 47.68 km2 to 70.88 km2, showing the opposite development of estuarine channels. Reduced riverine sediment supply may have been responsible for the estuarine channel erosion, and river engineering may have contributed to intense erosion in local areas. Also, the engineering projects were likely the main reason for the stability and growth of the sandbars. This study reveals the branching channel–sandbar system of the upper YRE in response to anthropogenic and climatic change forcing. The knowledge gained from this study can be applied to other similar estuarine systems around the world, helping develop sustainable strategies for the utilization and protection of the world’s estuaries and deltas.

Using a multi-layer snow model for transient paleo-studies: surface mass balance evolution during the Last Interglacial

Abstract. During the Quaternary, ice sheets experienced several retreat–advance cycles, strongly influencing climate patterns. In order to properly simulate these phenomena, it is preferable to use physics-based models instead of parameterizations to estimate the surface mass balance (SMB), which strongly influences the evolution of the ice sheet. To further investigate the potential of these SMB models, this work evaluates the BErgen Snow SImulator (BESSI), a multi-layer snow model with high computational efficiency, as an alternative to providing the SMB for the Earth system model iLOVECLIM for multi-millennial simulations as in paleo-studies. We compare the behaviors of BESSI and insolation temperature melt (ITM), an existing SMB scheme of iLOVECLIM during the Last Interglacial (LIG). Firstly, we validate the two SMB models using the regional climate model Modèle Atmosphérique Régional (MAR) as forcing and reference for the present-day climate over the Greenland and Antarctic ice sheets. The evolution of the SMB over the LIG (130–116 ka) is computed by forcing BESSI and ITM with transient climate forcing obtained from iLOVECLIM for both ice sheets. For present-day climate conditions, both BESSI and ITM exhibit good performance compared to MAR despite a much simpler model setup. While BESSI performs well for both Antarctica and Greenland for the same set of parameters, the ITM parameters need to be adapted specifically for each ice sheet. This suggests that the physics embedded in BESSI allows better capture of SMB changes across varying climate conditions, while ITM displays a much stronger sensitivity to its tunable parameters. The findings suggest that BESSI can provide more reliable SMB estimations for the iLOVECLIM framework to improve the model simulations of the ice sheet evolution and interactions with climate for multi-millennial simulations.