High Latitudes Of Northern Hemisphere Research Articles

Historical fragmentation and stepping-stone gene flow led to population genetic differentiation in a coastal seabird.

Understanding the forces that shape population genetic structure is fundamental both for understanding evolutionary trajectories and for conservation. Many factors can influence the geographic distribution of genetic variation, and the extent to which local populations differ can be especially difficult to predict in highly mobile organisms. For example, many species of seabirds are essentially panmictic, but some show strong structure. Pigeon Guillemots (Cepphus columba; Charadriiformes: Alcidae) breed in small colonies scattered along the North Pacific coastline and feed in shallow nearshore waters year-round. Given their distribution, gene flow is potentially lower and population genetic structure is stronger than in most other high-latitude Northern Hemisphere seabirds. We screened variation in the mitochondrial control region, four microsatellite loci, and two nuclear introns in 202 Pigeon Guillemots representing three of five subspecies. Mitochondrial sequences and nuclear loci both showed significant population differences, although structure was weaker for the nuclear loci. Genetic differentiation was correlated with geographic distance between sampling locations for both the mitochondrial and nuclear loci. Mitochondrial gene trees and demographic modeling both provided strong evidence for two refugial populations during the Pleistocene glaciations: one in the Aleutian Islands and one farther east and south. We conclude that historical fragmentation combined with a stepping-stone model of gene flow led to the relatively strong population differentiation in Pigeon Guillemots compared to other high-latitude Northern Hemisphere seabird species. Our study adds to growing evidence that Pleistocene glaciation events affected population genetic structure not only in terrestrial species but also in coastal marine animals.

Records of deep-sea turbidity current activity in the Bengal Fan since the Last Glacial Maximum

The long-term evolution of deep-sea turbidity current activity is closely related to climate and sea level changes; however, the impact of abrupt climate change (e.g. millennial-scale events in high northern latitudes) is poorly known. In this paper, deep-sea turbidite records in the western part of the lower Bengal Fan were identified since the Last Glacial Maximum (LGM) to investigate the effects of abrupt climate change on the development of the Earth's largest deep-sea fan. Our records show a termination of turbidite activity in the western lower fan at 16.6 ka–15.4 ka almost contemporaneous with Heinrich 1 event (a cooling stadial in high northern latitudes). The trigger of this termination in turbidite activity may have been a sharp decrease in erosion rates during a time of relatively stable sea level and rapid source-sink processes. The subsequent episodes of the Bolling/Allerod warm interstadial and Younger Dryas cold stadial and the rapid sea level rise event that followed possibly induced adjustment of turbidity current activities in the Bengal Fan, as indicated by other published records. In summary, we show that close links exist between abrupt climate changes in the high-latitude Northern Hemisphere and deep-sea turbidity current activity in the low-latitude South Asia.

Volcanic forcing of high-latitude Northern Hemisphere eruptions

High-latitude explosive volcanic eruptions can cause substantial hemispheric cooling. Here, we use a whole-atmosphere chemistry-climate model to simulate Northern Hemisphere (NH) high-latitude volcanic eruptions of magnitude similar to the 1991 Mt. Pinatubo eruption. Our simulations reveal that the initial stability of the polar vortex strongly influences sulphur dioxide lifetime and aerosol growth by controlling the dispersion of injected gases after such eruptions in winter. Consequently, atmospheric variability introduces a spread in the cumulative aerosol radiative forcing of more than 20%. We test the aerosol evolution’s sensitivity to co-injection of sulphur and halogens, injection season, and altitude, and show how aerosol processes impact radiative forcing. Several of these sensitivities are of similar magnitude to the variability stemming from initial conditions, highlighting the significant influence of atmospheric variability. We compare the modelled volcanic sulphate deposition over the Greenland ice sheet with the relationship assumed in reconstructions of past NH eruptions. Our analysis yields an estimate of the Greenland transfer function for NH extratropical eruptions that, when applied to ice core data, produces volcanic stratospheric sulphur injections from NH extratropical eruptions 23% smaller than in currently used volcanic forcing reconstructions. Furthermore, the transfer function’s uncertainty, which propagates into the estimate of sulphur release, needs to be at least doubled to account for atmospheric variability and unknown eruption parameters. Our results offer insights into the processes shaping the climatic impacts of NH high-latitude eruptions and highlight the need for more accurate representation of these events in volcanic forcing reconstructions.

Tree diversity and arbuscular mycorrhizal trees increase soil carbon sequestration and stability in 1-m soils as regulated by microbial CAZymes-coworking in high-latitude Northern Hemisphere forests

Biodiversity loss and tree alternations often occurred in high-latitude Northern Hemisphere forests owing to climatic changes and human disturbance, while their effects on soil carbon sequestration remain unclear. In this paper, tree richness and arbuscular mycorrhizal (AM)-tree dominance experiments were settled in an experimental forest, and soil organic carbon (SOC) and glomalin-related soil protein carbon (Total, TG-C and easily extracted, EEG-C), stability (heterotrophic respiration, Rh, temperature sensitivity, Q10 and humidity sensitivity, Hs), in situ soil CO2, CH4, N2O fluxes, and CAZymes activities from the microbial metagenome technique were measured to identify their impacts and underlying mechanism. Both analysis of variance (ANOVA) and linear regression found tree richness and AM tree loss accompanied by soil carbon sequestration loss of total SOC storage, their mycorrhizal components (TG-C) and Rh. In 0–20 cm soils, high tree richness quadrats had 16–126.6 % higher SOC, TG-C, Rh, and in situ N2O flux, while AM-dominated stands had 34–39 % higher SOC and Rh than the EcM-dominated stands. In the 1 m soil profile, the effect size from tree richness and AM trees were more evident than the 0–20 cm soils. Compared with the richness gradient, much significant differences occurred between AM- and EcM-dominated stands. Structural equation modeling found that tree richness directly improved C stability, while the SOC accrual from the tree richness enrichment and AM-tree dominance were indirectly achieved by their decreasing in multiple CAZymes activities. Of CAZymes, glycoside hydrolases, polysaccharide lyases, carbohydrate esterases, glycosyl transferases, auxiliary activities, and carbohydrate-binding modules cooperated in their regulation of the soil C accrual. Our findings support carbon sequestration via biodiversity conservation and proper forest management related to tree mycorrhizal symbionts.

Tree growth and density enhanced, while diversity and spatial clustering reduced soil mycorrhizal C and N sequestration: Strong interaction with soil properties in northeastern China

In this paper, the effects of species diversity, tree growth, and spatial clustering on mycorrhizal carbon and nitrogen sequestration and the interaction of soil physicochemical properties in Northeast China were investigated. Based on 720 10 m ∗ 10 m plots in Harbin Experimental Forest Farm of Northeast Forestry University, we determined mycorrhizal biomarkers of easily extractable Glomalin-related soil protein (EEG) and total Glomalin-related soil protein (TG). Four plant diversity indices, seven structural metrics, and five soil properties were also measured. We found that: 1) The low tree diversity plots had 1.08–1.23 times higher TG, EEG, TG-N/TN (proportion of N in TG to TN), and TG-C/SOC (proportion of C in TG to SOC) than the high plots. 2) Tree diameter was negatively correlated with EEG and TG, but positively correlated with the EEG and TG contribution to soil TN and SOC. Soil EEG and TG were positively correlated with under-branch height and tree density. W (Uniform Angle Index, higher W indicates more clustering of tree distribution in the plot) was negatively correlated with the above four ratios and positively correlated with EEG/TG. 3) pH was the most powerful explainer for the GRSP variations (6.8 %, strongest negative association with GRSP/TN, R2 > 0.13), followed by soil electrical conductance (6.5 %, positive relation with TG, p < 0.05), AP (3.2 %). 4) Plant diversity mainly affected GRSP traits through the interaction with soils (0.07), tree growth and density directly increased TG, TG-N/TN, and TG-C/SOC, while tree spatial distribution directly reduced TG-N/TN. Our finding highlighted the important effects of tree diversity and forest structural traits on GRSP amount, carbon sequestration, and nutrient retentions, and could support glomalin-related forest soil management of temperate forests in the high-latitude northern hemisphere.

Biomass carbon sink stability of conifer and broadleaf boreal forests: differently associated with plant diversity and mycorrhizal symbionts?

Forest biomass carbon stability is crucial in achieving carbon neutrality in the high-latitude northern hemisphere, and identifying the differences among forest types and decoupling their associations with plant traits and geoclimatic conditions is the basis for precise forest management. We conducted a large-scale field survey in state-owned forest areas in northeastern China, covering a total of 280,000 km2 forest area, 1275 arbor plots (30m × 30m), 5285 shrub plots (5m × 5m), and 7076 herb plots (1m × 1m). We hypothesized that the conifer and broadleaf forest differences in biomass carbon (C) storage and stability (environmental stability to climatic changes-ES and recalcitrant stability to be decomposed-RS) are associated with mycorrhizal abundance (EcM: ectomycorrhizal, AM: arbuscular mycorrhizal, NM-AM: non-mycorrhizal or arbuscular mycorrhizal), taxon diversity traits (richness, Simpson, Shannon-Wiener, and evenness), and structural differences (diameter, height, and density) in the arbor, shrub, and herb layers. Our results showed that (1) conifer forests had 13.1Mg/ha higher C stocks and 30.9% higher RS, but 8.6% lower ES than broadleaf forests (p < 0.05). Trees in conifer forests had 1.5m taller and 2.4cm thicker trees, but 15% less tree density than those in broadleaf forests. Herbs in conifer forests were 14% shorter and 57% denser than in broadleaf forests. (2) The abundance of EcM-symbiont trees in conifer forests was 15% higher than in broadleaf forests, while their EcM-symbiont shrubs and AM-symbiont herbs were 5-6% lower (p < 0.05). Broadleaf forests had 7% higher tree richness and 19% higher herb richness but 9% lower shrub richness than conifer forests (p < 0.05). Tree and herb evenness was 5-6% higher in conifer forests (p < 0.05). (3) Variations of biomass C sink traits could be explained more by plant diversity in conifer forests (7%) than in broadleaf forests (3.4%). Mycorrhizal symbionts could explain more in broadleaf forests (9.7%) than conifer forests (6.7%). In conifer forests, fewer EcM trees (higher AM trees) and AM herbs, higher tree richness were accompanied by higher biomass C storage and ES. Broadleaf forests underwent similar changes, characterized by an elevation in both RS and ES. (4) Our research emphasized that variations in carbon sequestration between conifer and broadleaf forests could be attributed to mycorrhizal symbionts and species diversity besides tree size-related structural differences. Our findings support the precise management of boreal forests to achieve carbon neutrality based on leaf blade types, plant diversity, and mycorrhizal symbionts.

A 1500-year record of mercury isotopes in seal feces documents sea ice changes in the Antarctic

Temporal and spatial variations in sea ice coverage at high Northern Hemisphere latitudes have been shown to affect the photodegradation of methylmercury in seawater and the mercury isotope signatures in biological samples, suggesting the potential of mercury isotopes to reconstruct sea ice variability. Here we study the mercury isotopic composition of a 1500-year sediment profile strongly affected by seal activities on the Fildes Peninsula, King George Island, Antarctic Peninsula. The mass independent isotope fractionation of mercury (represented by Δ199Hg) in sediments dominated by seal feces input reflects the Δ199Hg of marine methylmercury before entering the food web, documenting the changes in the degree of photodemethylation. We found much higher Δ199Hg in sediments deposited during a warm period (~700-1000 years ago), suggesting that reduced sea ice promoted greater photodemethylation. Thus, this study demonstrates the modulation of methylmercury photodegradation by sea ice in the Antarctic, and that mercury isotopes can record historical sea ice changes.

Impacts of a weakened AMOC on precipitation over the Euro-Atlantic region in the EC-Earth3 climate model

Given paleoclimatic evidence that the Atlantic Meridional Overturning Circulation (AMOC) may affect the global climate system, we conduct model experiments with EC-Earth3, a state-of-the-art GCM, to specifically investigate, for the first time, mechanisms of precipitation change over the Euro-Atlantic sector induced by a weakened AMOC. We artificially weaken the strength of the AMOC in the model through the release of a freshwater anomaly into the Northern Hemisphere high latitude ocean, thereby obtaining a ~ 57% weaker AMOC with respect to its preindustrial strength for 60 model years. Similar to prior studies, we find that Northern Hemisphere precipitation decreases in response to a weakened AMOC. However, we also find that the frequency of wet days increases in some regions. By computing the atmospheric moisture budget, we find that intensified but drier storms cause less precipitation over land. Nevertheless, changes in the jet stream tend to enhance precipitation over northwestern Europe. We further investigate the association of precipitation anomalies with large-scale atmospheric circulations by computing weather regimes through clustering of geopotential height daily anomalies. We find an increase in the frequency of the positive phase of the North Atlantic Oscillation (NAO+), which is associated with an increase in the occurrence of wet days over northern Europe and drier conditions over southern Europe. Since a ~ 57% reduction in the AMOC strength is within the inter-model range of projected AMOC declines by the end of the twenty-first century, our results have implications for understanding the role of AMOC in future hydrological changes.

Farmland Shelterbelt Changes in Soil Properties: Soil Depth-Location Dependency and General Pattern in Songnen Plain, Northeastern China

As one of the world’s largest ecological rehabilitation programs, the three-north (Northern China, Northeastern China, and Northwestern China) shelterbelts program in China were not well evaluated on its effects on multiple soil properties. This paper aims to quantify this. Seven hundred twenty soils from paired plots of farmlands and neighbor shelterbelts were sampled from six regions of Songnen Plain in northeastern China. Multivariate analysis of variance and regression analysis were used to detect the impacts of shelterbelt plantations. For the overall 1 m soil profiles, shelterbelt plantations had a 4.3% and 7.4% decreases in soil bulk density and soil moisture (p = 0.000), a 4.8% increase in soil porosity (p = 0.003). It also evidently recovered soil fertility with a 40% increase in total P, a 4.4% increase in total K, and a 15.1% increase in available K (p &lt; 0.05). However, without overall changes were in SOC and N (p &gt; 0.05). Compared with farmland, shelterbelt plantations produced a 7.8% SOC increase in 20–40 cm soil and much more minor changes in surface soil (0–20 cm). Compared with the younger plantation, mature shelterbelts tended to sequestrate more SOC in soils (from a 0.11% decrease to a 3.31% increase) and recover total K from a 2.24% decline to a 16.5% increase. Correlation analysis manifested that there is a significant relationship between SOC sequestration and the changes in bulk density, porosity, soil moisture, pH, EC, total N, total P, and alkaline hydrolyzed N. In contrast, the strongest relationship was observed between total N and SOC (r &gt; 0.50, p &lt; 0.001). The increase in total N was accompanied by 1.01–1.67-fold higher SOC sequestration in deep soils &gt;20 cm in poplar forests. Our results highlight that the over-40-year shelterbelts afforestation on farmland in northeastern China could strongly affect soil physics, soil water, and nutrient of P and K. The effects on SOC sequestration were dependent on soil depths, growth stages, and regions. Our data support the precise soil evaluation of agroforestry projects in the black soil region in the high-latitude northern hemisphere.

Analysis of Temperature Semi-Annual Oscillations (SAO) in the Middle Atmosphere

The middle atmosphere plays an important role in the research of various dynamical and energy processes. Microwave Limb Sounder (MLS), reanalyses and model simulations with NCAR’s Whole Atmosphere Community Climate Model (WACCM) data in the range between 100 and 0.1 hPa from 2005 to 2020 have been analyzed with a focus on the temperature semi-annual oscillations (SAO). Significant SAO of temperature is prominent in the tropical region (20°S–20°N) around 1–3 hPa, which is consistent with previous studies. We also found significant SAO in the northern hemisphere (NH) high latitudes between 8 and 0.3 hPa and southern hemisphere (SH) high latitudes between 0.5 and 0.1 hPa, which has been of less concern in previous studies. The thermal budget based on MERRA2 and simulations is used to explain the mechanism of SAO in the middle atmosphere. In the tropics, the two temperature peaks are mainly determined by radiative processes. In the NH high latitudes of the stratosphere, the temperature peak in January is mainly related to dynamical processes, while the temperature peak in July is determined by a combination of dynamical and radiative processes. In the NH high latitudes of the lower mesosphere, the first peak in June is primarily associated with dynamical and radiative processes, while the second peak in December is primarily associated with the dynamical processes. In the SH high latitudes of the lower mesosphere, the first temperature peak in July is mainly due to dynamical processes while the second temperature peak in December is mainly due to radiative processes. Various features are present in the SH and NH high latitude SAO in the lower mesosphere. Furthermore, we performed model simulations with and without SAO in sea surface temperatures (SST-SAO) to study the connection between SST and temperature SAO. WACCM6 results indicate that the SAO in the middle atmosphere is partially affected by the existence of an SST-SAO. By removing SAO in SST, the PSD magnitude of the SAO decreases in the tropical region and increases in the polar region. The amplitudes of total heating rates are also modified. The WACCM experiment confirms the relationship between SST-SAO and temperature SAO in the middle atmosphere.

A surface temperature dipole pattern between Eurasia and North America triggered by the Barents–Kara sea-ice retreat in boreal winter

The Arctic has experienced dramatic climate changes, characterized by rapid surface warming and sea-ice loss over the past four decades, with broad implications for climate variability over remote regions. Some studies report that Arctic warming may simultaneously induce a widespread cooling over Eurasia and frequent cold events over North America, especially during boreal winter. In contrast, other studies suggest a seesaw pattern of extreme temperature events with cold weather over East Asia accompanied by warm weather in North America on sub-seasonal time scales. It is unclear whether a systematic linkage in surface air temperature (SAT) exists between the two continents, let alone their interaction with Arctic sea ice. Here, we reveal a dipole pattern of SAT in boreal winter featuring a cooling (warming) in the Eurasian continent accompanied by a warming (cooling) in the North American continent, which is induced by an anomalous Barents–Kara sea-ice decline (increase). The dipole operates on interannual and multidecadal time scales. We find that an anomalous sea-ice loss over the Barents–Kara Seas triggers a wavenumber one atmospheric circulation pattern over the high-latitude Northern Hemisphere, with an anomalous high-pressure center over Siberia and an anomalous low-pressure center over high-latitude North America. The circulation adjustment generates the dipole temperature pattern through thermal advection. Our finding has important implications for Northern Hemisphere climate variability, extreme weather events, and their prediction and projection.

Responses of East Asian Winter Monsoon‐Australian Summer Monsoon to Local and Remote Orbital Forcing During Holocene

AbstractHere, we perform a set of sensitivity experiments in a climate model to quantify the impacts of local and remote insolation changes on the East Asian winter monsoon (EASM) and Australian summer monsoon (AusSM) at early and middle Holocene relative to the present. We show that the EAWM during Holocene is enhanced, driven overwhelmingly by the local insolation change in the low to mid‐latitude Northern Hemisphere (NH) through its impacts on land‐sea thermal contrast, with the NH high latitude forcing playing a negligible role. In contrast, the AusSM is also enhanced, opposite to the local insolation forcing, because the local forcing impact is overwhelmed by that from the remote forcing of both NH low latitude and Southern Hemisphere high latitude, with the latter dominating in the mid‐Holocene.

Effects of urbanization on woody plant phylogenetic diversity and its associations with landscape features in the high latitude northern hemisphere region, Northeast China

Urbanization is one of the primary drivers of terrestrial modification, with marked biological homogenization worldwide but relatively poor knowledge of woody phylogenetic diversity. Here, we investigated 943 plots, about 93,000 woody plants from 130 species in Northeast China, and calculated six phylogenetic diversity indexes, and urbanization landscape metrics; the responses of phylogenetic diversity to urbanization and its coupling relationship with landscape features were explored at 25 km × 25 km, 50 km × 50 km and 75 km × 75 km grid scales. We found that urbanization had enhanced the evolutionary distinctiveness of woody plants, characterizing as increasing Faith phylogenetic diversity (FPD) and their mean pairwise distance (MPD) while decreasing the mean nearest taxon distance (MNTD); these trends were independent of landscape scales and gymnosperm inclusion or not. As indicated by increasing SesMPD (Standardized MPD), the dominant role of community assemblage changed from environmental filtering in low urbanization intensity (UI) to competitive exclusion in high UI regions. Artificial surface area (ASA) and its percentage, SHAPE_F (Shape index of forest), and PD_F (Patch density of forest) had a threshold effect on phylogenetic diversity. ASA%, GDP (gross domestic product), and population density were the most potent predictors for the variations of phylogenetic diversity, and GDP contributed the most (42.9%). A higher GDP accompanied a higher FPD, SesPD (Standardized FPD), and SesMNTD (Standardized MNTD); higher PD_F and lower SHAPE_F were associated with higher MNTD, MPD, and SesMPD. In conclusion, urbanization strongly modifies woody plant phylogenetic diversity. Identifying the threshold effects and significant factors for phylogenetic variations allows biodiversity assessment and conservation through proper landscape configuration under the urbanization context.

Global Snowmelt Onset Reflects Climate Variability: Insights from Spaceborne Radiometer Observations

Abstract Snowmelt is a critical component in the cryosphere and has a direct impact on Earth’s energy and water budget. Here, a 40-yr integrated melt onset (MO) dataset over sea ice, ice sheets, and terrestrial snow is compiled from spaceborne microwave radiometers and ERA5, allowing an overall assessment of the cryosphere. Results suggest that MO in both hemispheres shows latitudinal and vertical zonalities. The global cryosphere presented a trend toward earlier MO (−2 days decade−1) with hotpots distributed at the Northern Hemisphere high latitudes where the warming rate is much higher than that at lower latitudes. Overall, variations in MO showed a similar pattern to that in near-surface temperature. The advance of MO has been slowing down since the 1990s and no significant trend was observed during the so-called warming hiatus period (1998–2012). Regionally, climatic linkage analyses suggest the local MO variations were associated with different climate indices. MO in the pan-Arctic region is related with the Arctic Oscillation and North Atlantic Oscillation, while that in the pan-Antarctic region is associated with El Niño–Southern Oscillation and the southern annular mode. Occasionally, abnormal MO occurs as a result of extreme weather conditions. In February 2018, abnormal early melt events that occurred in the Arctic Ocean are found to be linked with the warm southerly flow due to sudden stratospheric warming. These findings suggest the satellite-based MO allows examining the dynamics and extremes in the climate system, both regionally and globally.

Stratospheric ozone response to sulfate aerosol and solar dimming climate interventions based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) simulations

Abstract. This study assesses the impacts of stratospheric aerosol intervention (SAI) and solar dimming on stratospheric ozone based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) experiments, called G6sulfur and G6solar. For G6sulfur, an enhanced stratospheric sulfate aerosol burden reflects some of the incoming solar radiation back into space to cool the surface climate, while for G6solar, the reduction in the global solar constant in the model achieves the same goal. Both experiments use the high emissions scenario of SSP5-8.5 as the baseline experiment and define surface temperature from the medium emission scenario of SSP2-4.5 as the target. In total, six Earth system models (ESMs) performed these experiments, and three out of the six models include interactive stratospheric chemistry. The increase in absorbing sulfate aerosols in the stratosphere results in a heating of the lower tropical stratospheric temperatures by between 5 to 13 K for the six different ESMs, leading to changes in stratospheric transport, water vapor, and other related changes. The increase in the aerosol burden also increases aerosol surface area density, which is important for heterogeneous chemical reactions. The resulting changes in the springtime Antarctic ozone between the G6sulfur and SSP5-8.5, based on the three models with interactive chemistry, include an initial reduction in total column ozone (TCO) of 10 DU (ranging between 0–30 DU for the three models) and up to 20 DU (between 10–40 DU) by the end of the century. The relatively small reduction in TCO for the multi-model mean in the first 2 decades results from variations in the required sulfur injections in the models and differences in the complexity of the chemistry schemes. In contrast, in the Northern Hemisphere (NH) high latitudes, no significant changes can be identified due to the large natural variability in the models, with little change in TCO by the end of the century. However, all three models with interactive chemistry consistently simulate an increase in TCO in the NH mid-latitudes up to 20 DU, compared to SSP5-8.5, in addition to the 20 DU increase resulting from increasing greenhouse gases between SSP2-4.5 and SSP5-8.5. In contrast to G6sulfur, G6solar does not significantly change stratospheric temperatures compared to the baseline simulation. Solar dimming results in little change in TCO compared to SSP5-8.5. Only in the tropics does G6solar result in an increase of TCO of up to 8 DU, compared to SSP2-4.5, which may counteract the projected reduction in SSP5-8.5. This work identifies differences in the response of SAI and solar dimming on ozone for three ESMs with interactive chemistry, which are partly due to the differences and shortcomings in the complexity of aerosol microphysics, chemistry, and the description of ozone photolysis. It also identifies that solar dimming, if viewed as an analog to SAI using a predominantly scattering aerosol, would succeed in reducing tropospheric and surface temperatures, but any stratospheric changes due to the high forcing greenhouse gas scenario, including the potential harmful increase in TCO beyond historical values, would prevail.

Extreme Precipitation on Consecutive Days Occurs More Often in a Warming Climate

Abstract Extreme precipitation occurring on consecutive days may substantially increase the risk of related impacts, but changes in such events have not been studied at a global scale. Here we use a unique global dataset based on in situ observations and multimodel historical and future simulations to analyze the changes in the frequency of extreme precipitation on consecutive days (EPCD). We further disentangle the relative contributions of variations in precipitation intensity and temporal correlation of extreme precipitation to understand the processes that drive the changes in EPCD. Observations and climate model simulations show that the frequency of EPCD is increasing in most land regions, in particular, in North America, Europe, and the Northern Hemisphere high latitudes. These increases are primarily a consequence of increasing precipitation intensity, but changes in the temporal correlation of extreme precipitation regionally amplify or reduce the effects of intensity changes. Changes are larger in simulations with a stronger warming signal, suggesting that further increases in EPCD are expected for the future under continued climate warming.

Northern Hemisphere atmospheric history of carbon monoxide since preindustrial times reconstructed from multiple Greenland ice cores

Abstract. Carbon monoxide (CO) is a regulated pollutant and one of the key components determining the oxidizing capacity of the atmosphere. Obtaining a reliable record of atmospheric CO mixing ratios ([CO]) since preindustrial times is necessary to evaluate climate–chemistry models under conditions different from today and to constrain past CO sources. We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet that experience a range of snow accumulation rates, mean surface temperatures, and different chemical compositions. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled with continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019. Overall, continuous flow analysis (CFA) of CO was carried out on over 700 m of ice. The CFA-based CO measurements exhibit excellent external precision (ranging from 3.3 to 6.6 ppbv, 1σ) and achieve consistently low blanks (ranging from 4.1±1.2 to 12.6±4.4 ppbv), enabling paleoatmospheric interpretations. However, the five CO records all exhibit variability that is too large and rapid to reflect past atmospheric mixing ratio changes. Complementary tests conducted on discrete ice samples demonstrate that these variations are not artifacts of the analytical method (i.e., production of CO from organics in the ice during melting) but are very likely related to in situ CO production within the ice before analysis. Evaluation of the signal resolution and co-investigation of high-resolution records of CO and total organic carbon (TOC) suggest that past atmospheric CO variations can be extracted from the records' baselines with accumulation rates higher than 20 cm w.e.yr-1 (water equivalent per year). Consistent baseline CO records from four Greenland sites are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from 1700 to 1957 CE. Such a reconstruction should be taken as an upper bound of past atmospheric CO abundance. From 1700 to 1875 CE, the record reveals stable or slightly increasing values in the 100–115 ppbv range. From 1875 to 1957 CE, the record indicates a monotonic increase from 114±4 to 147±6 ppbv. The ice core multisite CO record exhibits an excellent overlap with the atmospheric CO record from Greenland firn air which spans the 1950–2010 CE time period. The combined ice core and firn air CO history, spanning 1700–2010 CE, provides useful constraints for future model studies of atmospheric changes since the preindustrial period.

Local Insolation Drives Afro‐Asian Monsoon at Orbital‐Scale in Holocene

AbstractInsolation changes play an important role in driving monsoon changes at orbital time scales. One key issue that has remained outstanding is whether the Asian monsoon is driven by local insolation from the Northern Hemisphere (NH) or remote insolation from the Southern Hemisphere (SH) at orbital band. Here, we perform a set of sensitivity experiments to quantify the impacts of local and remote insolation changes on the Afro‐Asian summer monsoon at 11 ka BP relative to the present. We show that the Afro‐Asian summer monsoon is overwhelmingly driven by the precession induced local insolation change in the tropical‐subtropical NH. The insolation from NH high latitudes also affects the Afro‐Asian summer monsoon. In contrast, the insolation from SH plays a negligible role. Our model experiments support the idea that the Afro‐Asian summer monsoon are driven predominantly by the direct forcing of NH low latitudes summer insolation for the Holocene.

Possible consequences of climate change on global water resources stored in dam reservoirs

Construction of dams and transformation of rivers, not only affects river-related and adjacent habitats, but also establishes new threats to surface freshwater resources globally. Predicted climate changes and increase of mean annual temperature will affect thermal regimes of dam reservoir ecosystems, severely altering their functioning. Analyzing three projections of representative concentration pathway (RCP 4.5, 6.0 and 8.5) for period of 2061–2080, we found that mean annual temperature at dam reservoir locations will increase by 3.06 °C to 4.74 °C from present. The highest projected increase of temperature was identified for dam reservoirs located in high latitudes of Northern Hemisphere, and therefore dam reservoirs located there will be most significantly affected. Numerous consequences of temperature increase are already recorded. Further increase will amplify unfavorable effects on numerous ecosystems, including dam reservoirs which are built on the purpose of the human population development. Our study indicates a threat for artificially stored water globally, with special attention to high latitudes in northern hemisphere and latitudes close to 200S meridian in southern hemisphere.

Abrupt Indian summer monsoon shifts aligned with Heinrich events and D-O cycles since MIS 3

The tropics experienced a unique monsoon climate that drove important changes in socio-economic conditions and shaped different phases of human history during the late Quaternary across the Indian subcontinent. This study presents a new high-resolution speleothem-record of Indian summer monsoon (ISM) variability ranging from ~45,000 to 34,000 yr BP combined with a published record up to 5500 yr BP from the Mawmluh cave, northeastern India. We document significant changes in solar insolation and precession harmonics, implicating solar activity as one of the major forcing factors for rapid monsoonal shifts. Our new δ 18 O time series shows high-amplitude shifts in the ISM during the marine isotope stage 3 (MIS 3), similar to Dansgaard-Oeschger (D-O) oscillations recorded at high northern latitudes, which mimic the Greenland ice sheet record. The sun driven Northern Hemisphere high latitude climate anomalies played an active role in driving ISM variability and changes in the regional hydrological cycle on centennial to millennial time scales across the Indian subcontinent. • Longest isotope record of speleothem from the South Asian region • Saw-tooth like isotope variability during MIS 3 • Changes in the NH temperatures impacted the hydroclimatic conditions in the Indian subcontinent. • Source region and transport pathways controlled the speleothem isotopic composition.