Opinion: Cloud-phase climate feedback and the importance of ice-nucleatingparticles Atmospheric Chemistry and Physics DOI 10.5194/acp-21-665-2021 5 February 2021 Shallow clouds covering vast areas of the world’s middle- and high-latitude oceans play a key role in dampening the global temperaturerise associated with CO2. These clouds, which contain both ice andsupercooled water, respond to a warming world by transitioning to a statewith more liquid water and a greater albedo, resulting in a negative“cloud-phase” climate feedback component. Here we argue that the magnitudeof the negative cloud-phase feedback component depends on the amount andnature of the small fraction of aerosol particles that can nucleate icecrystals. We propose that a concerted research effort is required to reducesubstantial uncertainties related to the poorly understoodsources, concentration, seasonal cycles and nature of these ice-nucleatingparticles (INPs) and their rudimentary treatment in climate models. Thetopic is important because many climate models may have overestimated themagnitude of the cloud-phase feedback, and those with better representationof shallow oceanic clouds predict a substantially larger climate warming. Wemake the case that understanding the present-day INP population in shallowclouds in the cold sector of cyclone systems is particularly critical fordefining present-day cloud phase and therefore how the clouds respond towarming. We also need to develop a predictive capability for future INPemissions and sinks in a warmer world with less ice and snow and potentiallystronger INP sources. Read more
ModIs Dust AeroSol (MIDAS): a global fine-resolution dust optical depth data set Atmospheric Measurement Techniques DOI 10.5194/amt-14-309-2021 4 February 2021 Monitoring and describing the spatiotemporal variability in dust aerosols is crucial for understanding their multiple effects, related feedbacks, and impacts within the Earth system. This study describes the development of the ModIs Dust AeroSol (MIDAS) data set. MIDAS provides columnar daily dust optical depth (DOD) at 550 nm at a global scale and fine spatial resolution (0.1∘ × 0.1∘) over a 15-year period (2003–2017). This new data set combines quality filtered satellite aerosol optical depth (AOD) retrievals from MODIS-Aqua at swath level (Collection 6.1; Level 2), along with DOD-to-AOD ratios provided by the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) reanalysis to derive DOD on the MODIS native grid. The uncertainties of the MODIS AOD and MERRA-2 dust fraction, with respect to the AEronet RObotic NETwork (AERONET) and LIdar climatology of vertical Aerosol Structure for space-based lidar simulation (LIVAS), respectively, are taken into account for the estimation of the total DOD uncertainty. MERRA-2 dust fractions are in very good agreement with those of LIVAS across the dust belt in thetropical Atlantic Ocean and the Arabian Sea; the agreement degrades in North America and the Southern Hemisphere, where dust sources are smaller. MIDAS, MERRA-2, and LIVAS DODs strongly agree when it comes to annual and seasonal spatial patterns, with colocated global DOD averages of 0.033, 0.031, and 0.029, respectively; however, deviations in dust loading are evident and regionally dependent. Overall, MIDAS is well correlated with AERONET-derived DODs (R=0.89) and only shows a small positive bias (0.004 or 2.7 %). Among the major dust areas of the planet, the highest R values (>0.9) are found at sites of North Africa, the Middle East, and Asia. MIDAS expands, complements, and upgrades the existing observational capabilities of dust aerosols, and it is suitable for dust climatological studies, model evaluation, and data assimilation. Read more
On the ice-nucleating potential of warm hydrometeors in mixed-phase clouds Atmospheric Chemistry and Physics DOI 10.5194/acp-21-561-2021 3 February 2021 The question as to whether or not the presence of warm hydrometeors in clouds mayplay a significant role in the nucleation of new ice particles has been debatedfor several decades. While the early works of and indicated that it might be irrelevant, the more recentstudy of suggested otherwise. In this work, weattempt to quantify the ice-nucleating potential using high-fidelity flowsimulation techniques around a single hydrometeor and use favorable considerationsto upscale the effects to a collective of ice particles in clouds. While we find that ice nucleationmay be significantly enhanced in the vicinity of a warm hydrometeorand that the affected volume of air is much larger than previously estimated, it isunlikely that this effect alone causes the rapidenhancement of ice nucleation observed in some types of clouds, mainly due to the lowinitial volumetric ice concentration. Furthermore, it is demonstrated that the excess nucleationrate does not primarily depend on the rate at which cloud volume is sampled by the meteors’wakes but is rather limited by the exposure time of ice-nucleating particles to the wake,which is estimated to be of the order of few microseconds. It is suggested to further investigatethis phenomenon by tracking the trajectories of ice-nucleating particles in order to obtaina parametrization which can be implemented into existing cloud models to investigate second-order effectssuch as ice enhancement after the onset of glaciation. Read more
Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing Atmospheric Chemistry and Physics DOI 10.5194/acp-21-535-2021 2 February 2021 In June 2019 a stratospheric eruption occurred at Raikoke (48∘ N,153∘ E). Satellite observations show the injection of ash and SO2 into the lower stratosphere and an early entrainment of the plume into a cyclone. Following the Raikoke eruption, stratospheric aerosol optical depth (sAOD) values increased in the whole Northern Hemisphere and tropics and remained enhanced for more than 1 year, with peak values at 0.040 (short-wavelength, high northern latitudes) to 0.025 (short-wavelength, Northern Hemisphere average). Discrepancies between observations and global model simulations indicate that ash may have influenced the extent and evolution of the sAOD. Top of the atmosphere radiative forcings are estimated at values between -0.3 and -0.4Wm-2 (clear-sky) and of -0.1 to -0.2Wm-2 (all-sky), comparable to what was estimated for the Sarychev eruption in 2009. Almost simultaneously two significantly smaller stratospheric eruptions occurred at Ulawun (5∘ S, 151∘ E) in June and August. Aerosol enhancements from the Ulawun eruptions mainly had an impact on the tropics and Southern Hemisphere. The Ulawun plume circled the Earth within 1 month in the tropics. Peak shorter-wavelength sAOD values at 0.01 are found in the tropics following the Ulawun eruptions and a radiative forcing not exceeding -0.15 (clear-sky) and -0.05 (all-sky). Compared to the Canadian fires (2017), Ambae eruption (2018), Ulawun (2019) and the Australian fires (2019/2020), the highest sAOD and radiative forcing values are found for the Raikoke eruption. Read more
Fire and vegetation dynamics in northwest Siberia during the last 60 years based on high-resolution remote sensing Biogeosciences DOI 10.5194/bg-18-207-2021 1 February 2021 The rapidly warming Arctic undergoes transitions that can influence global carbon balance. One of the key processes is the shift towards vegetation types with higher biomass underlining a stronger carbon sink. The shift is predicted by bioclimatic models based on abiotic climatic factors, but it is not always confirmed with observations. Recent studies highlight the role of disturbances in the shift. Here we use high-resolution remote sensing to study the process of transition from tundra to forest and its connection to wildfires in the 20 000 km2 area in northwest Siberia. Overall, 40 % of the study area was burned during a 60-year period. Three-quarters of the burned areas were dry tundra. About 10 % of the study area experienced two–three fires with an interval of 15–60 years suggesting a shorter fire return interval than that reported earlier for the northern areas of central Siberia (130–350 years). Based on our results, the shift in vegetation (within the 60-year period) occurred in 40 %–85 % of the burned territories. All fire-affected territories were flat; therefore no effect of topography was detected. Oppositely, in the undisturbed areas, a transition of vegetation was observed only in 6 %–15 % of the territories, characterized by steeper topographic slopes. Our results suggest a strong role of disturbances in the tree advance in northwest Siberia. Read more
Millennial-age glycerol dialkyl glycerol tetraethers (GDGTs) in forested mineral soils: 14C-based evidence for stabilization of microbial necromass Biogeosciences DOI 10.5194/bg-18-189-2021 29 January 2021 Understanding controls on the persistence of soil organic matter (SOM) is essential to constrain its role in the carbon cycle and inform climate–carbon cycle model predictions. Emerging concepts regarding the formation and turnover of SOM imply that it is mainly comprised of mineral-stabilized microbial products and residues; however, direct evidence in support of this concept remains limited. Here, we introduce and test a method for the isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) – diagnostic membrane lipids of archaea and bacteria, respectively – for subsequent natural abundance radiocarbon analysis. The method is applied to depth profiles from two Swiss pre-Alpine forested soils. We find that the Δ14C values of these microbial markers markedly decrease with increasing soil depth, indicating turnover times of millennia in mineral subsoils. The contrasting metabolisms of the GDGT-producing microorganisms indicates it is unlikely that the low Δ14C values of these membrane lipids reflect heterotrophic acquisition of 14C-depleted carbon. We therefore attribute the 14C-depleted signatures of GDGTs to their physical protection through association with mineral surfaces. These findings thus provide strong evidence for the presence of stabilized microbial necromass in forested mineral soils. Read more
Increased carbon capture by a silicate-treated forested watershed affected by acid deposition Biogeosciences DOI 10.5194/bg-18-169-2021 28 January 2021 Meeting internationally agreed-upon climate targets requirescarbon dioxide removal (CDR) strategies coupled with an urgent phase-down offossil fuel emissions. However, the efficacy and wider impacts of CDR arepoorly understood. Enhanced rock weathering (ERW) is a land-based CDRstrategy requiring large-scale field trials. Here we show that a low 3.44 t ha-1 wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO2 ha-1 over 15 years. Despite a 0.8–2.4 t CO2 ha-1 logistical carbon penalty from mining,grinding, transportation, and spreading, by 2015 weathering together withincreased forest productivity led to net CDR of 8.5–11.5 t CO2 ha-1. Our results demonstrate that ERW may be an effective, scalableCDR strategy for acid-impacted forests but at large scales requiressustainable sources of silicate rock dust. Read more
Intercomparison of freshwater fluxes over ocean and investigations into water budget closure Hydrology and Earth System Sciences DOI 10.5194/hess-25-121-2021 27 January 2021 The net exchange of water between the surface and atmosphere is mainly determined by the freshwater flux: the difference between evaporation ( E ) and precipitation ( P ), or E−P . Although there is consensus among modelers that with a warming climate E−P will increase, evidence from satellite data is still not conclusive, mainly due to sensor calibration issues. We here investigate the degree of correspondence among six recent satellite-based climate data records and ERA5 reanalysis E−P data. Read more
Evaluating the dependence structure of compound precipitation and wind speed extremes Earth System Dynamics DOI 10.5194/esd-12-1-2021 26 January 2021 Compound extremes such as heavy precipitation and extreme winds can lead to large damage. To date it is unclear how well climate models represent such compound extremes. Here we present a new measure to assess differences in the dependence structure of bivariate extremes. This measure is applied to assess differences in the dependence of compound precipitation and wind extremes between three model simulations and one reanalysis dataset in a domain in central Europe. Read more
Glider-based observations of CO2 in the Labrador Sea Ocean Science DOI 10.5194/os-17-1-2021 25 January 2021 This paper describes challenges around the direct measurement of CO 2 in the ocean using ocean gliders. We discuss our method of using multiple sensor platforms as test beds to carry out observing experiments and highlight the implications of our study for future glider missions. We also show high-resolution measurements and discuss challenges and lessons learned in the context of future ocean gas measurements. Read more
Southern Ocean Biogeochemical Argo detect under-ice phytoplankton growth before sea ice retreat Biogeosciences DOI 10.5194/bg-18-25-2021 22 January 2021 This paper examines the question of what causes the rapid spring growth of microscopic marine algae (phytoplankton) in the ice-covered ocean surrounding Antarctica. One prominent hypothesis proposes that the melting of sea ice is the primary cause, while our results suggest that this is only part of the explanation. In particular, we show that phytoplankton are able to start growing before the sea ice melts appreciably, much earlier than previously thought. Read more
Plateaus and jumps in the atmospheric radiocarbon record – potential origin and value as global age markers for glacial-to-deglacial paleoceanography, a synthesis Climate of the Past DOI 10.5194/cp-16-2547-2020 21 January 2021 The dating technique of 14 C plateau tuning uses U/Th-based model ages, refinements of the Lake Suigetsu age scale, and the link of surface ocean carbon to the globally mixed atmosphere as basis of age correlation. Our synthesis employs data of 20 sediment cores from the global ocean and offers a coherent picture of global ocean circulation evolving over glacial-to-deglacial times on semi-millennial scales to be compared with climate records stored in marine sediments, ice cores, and speleothems. Read more
Long-term deposition and condensation ice-nucleatingparticle measurements from four stations across the globe Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15983-2020 20 January 2021 Long-term ice-nucleating particle (INP) data are presented from four semi-pristine sites located in the Amazon, the Caribbean, Germany and the Arctic. Average INP concentrations did not differ by orders of magnitude between the sites. For all sites short-term variability dominated the time series, which lacked clear trends and seasonalities. Common drivers to explain the INP levels and their variations could not be identified, illustrating the complex nature of heterogeneous ice nucleation. Read more
Emergent constraints on equilibrium climate sensitivity in CMIP5: do they hold for CMIP6? Earth System Dynamics DOI 10.5194/esd-11-1233-2020 19 January 2021 As an important measure of climate change, the Equilibrium Climate Sensitivity (ECS) describes the change in surface temperature after a doubling of the atmospheric CO 2 concentration. Climate models from the Coupled Model Intercomparison Project (CMIP) show a wide range in ECS. Emergent constraints are a technique to reduce uncertainties in ECS with observational data. Emergent constraints developed with data from CMIP phase 5 show reduced skill and higher ECS ranges when applied to CMIP6 data. Read more
Brief communication: Heterogenous thinning and subglacial lake activity on Thwaites Glacier, West Antarctica The Cryosphere DOI 10.5194/tc-14-4603-2020 18 January 2021 The West Antarctic Ice Sheet has long been considered geometrically prone to collapse, and Thwaites Glacier, the largest glacier in the Amundsen Sea, is likely in the early stages of disintegration. Using observations of Thwaites Glacier velocity and elevation change, we show that the transport of ~2 km 3 of water beneath Thwaites Glacier has only a small and transient effect on glacier speed relative to ongoing thinning driven by ocean melt. Read more
Downsizing parameter ensembles for simulations of rare floods Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-3521-2020 15 January 2021 This work proposes methods for reducing the computational requirements of hydrological simulations for the estimation of very rare floods that occur on average less than once in 1000 years. These methods enable the analysis of long streamflow time series (here for example 10 000 years) at low computational costs and with modelling uncertainty. They are to be used within continuous simulation frameworks with long input time series and are readily transferable to similar simulation tasks. Read more
Biases in the albedo sensitivity to deforestation in CMIP5 models and their impacts on the associated historical radiative forcing Earth System Dynamics DOI 10.5194/esd-11-1209-2020 14 January 2021 Trees are darker than crops or grasses; hence, they absorb more solar radiation. Therefore, land cover changes modify the fraction of solar radiation reflected by the land surface (its albedo), with consequences for the climate. We apply a new statistical method to simulations conducted with 15 recent climate models and find that albedo variations due to land cover changes since 1860 have led to a decrease in the net amount of energy entering the atmosphere by −0.09 W m 2 on average. Read more
Quantifying CO2 emissions of a city with the Copernicus Anthropogenic CO2 Monitoring satellite mission Atmospheric Measurement Techniques DOI 10.5194/amt-13-6733-2020 13 January 2021 The European CO2M mission is a proposed constellation of CO 2 imaging satellites expected to monitor CO 2 emissions of large cities. Using synthetic observations, we show that a constellation of two or more satellites should be able to quantify Berlin’s annual emissions with 10–20 % accuracy, even when considering atmospheric transport model errors. We therefore expect that CO2M will make an important contribution to the monitoring and verification of CO 2 emissions from cities worldwide. Read more
New global characterisation of landslide exposure Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-3413-2020 12 January 2021 Landslides cause thousands of fatalities and cost billions of dollars of damage worldwide every year, but different inventories of landslide events can have widely diverging completeness. This can lead to spatial biases in our understanding of the impacts. Here we use a globally homogeneous model of landslide hazard and exposure to provide consistent estimates of where landslides are most likely to cause damage to people, roads and other critical infrastructure at 1 km resolution. Read more
Tropical Pacific climate variability under solar geoengineering: impacts onENSO extremes Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15461-2020 11 January 2021 Solar geoengineering has been introduced to mitigate human-caused global warming by reflecting sunlight back into space. This research investigates the impact of solar geoengineering on the tropical Pacific climate. We find that solar geoengineering can compensate some of the greenhouse-induced changes in the tropical Pacific but not all. In particular, solar geoengineering will result in significant changes in rainfall, sea surface temperatures, and increased frequency of extreme ENSO events. Read more
Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study Climate of the Past DOI 10.5194/cp-16-2459-2020 8 January 2021 We tested the applicability of the organic biomarker IPSO 25 for sea ice reconstructions in the industrial era at the western Antarctic Peninsula. We successfully evaluated our data with satellite sea ice observations. The comparison with marine and ice core records revealed that sea ice interpretations must consider climatic and sea ice dynamics. Sea ice biomarker production is mainly influenced by the Southern Annular Mode, while the El Niño–Southern Oscillation seems to have a minor impact. Read more
Optical characterization of pure pollen types using a multi-wavelength Raman polarization lidar Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15323-2020 7 January 2021 Measurements of the multi-wavelength Raman polarization lidar Polly XT have been combined with measurements of pollen type and concentration using a traditional pollen sampler at a rural forest site in Kuopio, Finland. The depolarization ratio was enhanced when there were pollen grains in the atmosphere, illustrating the potential of lidar to track pollen grains in the atmosphere. The depolarization ratio of pure pollen particles was assessed for birch and pine pollen using a novel algorithm. Read more
Combined use of Mie–Raman and fluorescence lidar observations for improving aerosol characterization: feasibility experiment Atmospheric Measurement Techniques DOI 10.5194/amt-13-6691-2020 6 January 2021 To study the feasibility of a fluorescence lidar for aerosol characterization, the fluorescence channel is added to the multiwavelength Mie-Raman lidar of Lille University. A part of the fluorescence spectrum is selected by the interference filter of 44 nm bandwidth centered at 466 nm. Such an approach has demonstrated high sensitivity, allowing fluorescence signals from weak aerosol layers to be detected. The technique can also be used for monitoring the aerosol inside the cloud layers. Read more
The dual-field-of-view polarization lidar technique: a new concept in monitoring aerosol effects in liquid-water clouds – theoretical framework Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15247-2020 5 January 2021 A novel lidar method to study cloud microphysical properties (of liquid water clouds) and to study aerosol–cloud interaction (ACI) is developed and presented in this paper. In Part 1, the theoretical framework including an error analysis is given together with an overview of the aerosol information that the same lidar system can obtain. The ACI concept based on aerosol and cloud information is also explained. Applications of the proposed approach to lidar measurements are presented in Part 2. Read more
Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting andlocating unstable rock slopes in a remote Arctic area Earth Surface Dynamics DOI 10.5194/esurf-8-1021-2020 4 January 2021 The 17 June 2017 Karrat landslide in Greenland caused a tsunami that killed four people. We apply a multidisciplinary workflow to reconstruct a timeline of events and find that three historic landslides occurred in 2009, 2016, and 2017. We also find evidence of much older periods of landslide activity. Three newly discovered active slopes might pose a future hazard. We speculate that the trigger for the recent events is melting permafrost due to a warming climate. Read more
Iron and aluminum association with microbially processed organic matter viameso-density aggregate formation across soils: organo-metallic gluehypothesis SOIL DOI 10.5194/soil-6-597-2020 1 January 2021 Global significance of metals (extractable Fe and Al phases) to control organic matter (OM) in recognized. Next key questions include the identification of their localization and mechanism behind OM–metal relationships. Across 23 soils of contrasting mineralogy, Fe and Al phases were mainly associated with microbially processed OM as meso-density microaggregates. OM- and metal-rich nanocomposites with a narrow OM : metal ratio likely acted as binding agents. A new conceptual model was proposed. Read more
The Antarctic sea ice cover from ICESat-2 and CryoSat-2: freeboard, snow depth, and ice thickness The Cryosphere DOI 10.5194/tc-14-4453-2020 31 December 2020 Our current understanding of Antarctic ice cover is largely informed by ice extent measurements from passive microwave sensors. These records, while useful, provide a limited picture of how the ice is responding to climate change. In this paper, we combine measurements from ICESat-2 and CryoSat-2 missions to assess snow depth and ice thickness of the Antarctic ice cover over an 8-month period (April through November 2019). The potential impact of salinity in the snow layer is discussed. Read more
The catastrophic thermokarst lake drainage events of 2018 in northwesternAlaska: fast-forward into the future The Cryosphere DOI 10.5194/tc-14-4279-2020 30 December 2020 In summer 2018, northwestern Alaska was affected by widespread lake drainage which strongly exceeded previous observations. We analyzed the spatial and temporal patterns with remote sensing observations, weather data and lake-ice simulations. The preceding fall and winter season was the second warmest and wettest on record, causing the destabilization of permafrost and elevated water levels which likely led to widespread and rapid lake drainage during or right after ice breaku Read more
Focus on glaciers: a geo-photo exposition of vanishing beauty Geoscience Communication DOI 10.5194/gc-3-381-2020 29 December 2020 We organized an exhibition on the climate crisis using high-quality images shot by scientists, who are amateur photographers, during their campaigns in glacier regions. Working-age people, attracted by the gorgeous images, received the message that such beauty is in danger of vanishing. Twice, the visitors could talk directly with the experts to discuss geoscience, photography, and aesthetic choices and, of course, climate change, a problem that each of us has to play a part in to solve. Read more
Investigating the sensitivity of soil heterotrophic respiration to recent snow cover changes in Alaska using a satellite-based permafrost carbon model Biogeosciences DOI 10.5194/bg-17-5861-2020 28 December 2020 We developed a 1 km satellite-data-driven permafrost carbon model to evaluate soil respiration sensitivity to recent snow cover changes in Alaska. Results show earlier snowmelt enhances growing-season soil respiration and reduces annual carbon uptake, while early cold-season soil respiration is linked to the number of snow-free days after the land surface freezes. Our results also show nonnegligible influences of subgrid variability in surface conditions on model-simulated CO 2 seasonal cycles. Read more
A systematic exploration of satellite radar coherence methods for rapid landslide detection Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-3197-2020 25 December 2020 Satellite radar could provide information on landslide locations within days of an earthquake or rainfall event anywhere on Earth, but until now there has been a lack of systematic testing of possible radar methods, and most methods have been demonstrated using a single case study event and data from a single satellite sensor. Here we test five methods on four events, demonstrating their wide applicability and making recommendations on when different methods should be applied in the future. Read more
New flood frequency estimates for the largest river in Norway based on the combination of short and long time series Hydrology and Earth System Sciences DOI 10.5194/hess-24-5595-2020 24 December 2020 We combine systematic, historical, and paleo information to obtain flood information from the last 10 300 years for the Glomma River in Norway. We identify periods with increased flood activity (4000–2000 years ago and the recent 1000 years) that correspond broadly to periods with low summer temperatures and glacier growth. The design floods in Glomma were more than 20 % higher during the 18th century than today. We suggest that trends in flood variability are linked to snow in late spring. Read more
Tectonic exhumation of the Central Alps recorded by detrital zircon in theMolasse Basin, Switzerland Solid Earth DOI 10.5194/se-11-2197-2020 23 December 2020 We present new U–Pb age data to provide insights into the source of sediment for the Molasse Sedimentary Basin in Switzerland. The paper aims to help shed light on the processes that built the Central Alpine Mountains between ~35 and ~15 Ma. A primary conclusion drawn from the results is that at ~21 Ma there was a significant change in the sediment sources for the basin. We feel this change indicates major tectonic changes within the Central Alps. Read more
Evaluation of Arctic warming in mid-Pliocene climate simulations Climate of the Past DOI 10.5194/cp-16-2325-2020 22 December 2020 The simulations for the past climate can inform us about the performance of climate models in different climate scenarios. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), when the CO 2 level was comparable to today. The results highlight the importance of slow feedbacks in the model simulations and imply that we must be careful when using simulations of the mPWP as an analogue for future climate change. Read more
Sensitivity of the Southern Hemisphere circumpolar jet response to Antarctic ozone depletion: prescribed versus interactive chemistry Atmospheric Chemistry and Physics DOI 10.5194/acp-20-14043-2020 21 December 2020 Ozone depletion over Antarctica was shown to influence the tropospheric jet in the Southern Hemisphere. We investigate the atmospheric response to ozone depletion comparing climate model ensembles with interactive and prescribed ozone fields. We show that allowing feedbacks between ozone chemistry and model physics as well as including asymmetries in ozone leads to a strengthened ozone depletion signature in the stratosphere but does not significantly affect the tropospheric jet position. Read more
Distinguishing the impacts of ozone and ozone-depleting substanceson the recent increase in Antarctic surface mass balance The Cryosphere DOI 10.5194/tc-14-4135-2020 18 December 2020 The increase in Antarctic surface mass balance (SMB, precipitation vs. evaporation/sublimation) is projected to mitigate sea-level rise. Here we show that nearly half of this increase over the 20th century is attributed to stratospheric ozone depletion and ozone-depleting substance (ODS) emissions. Our results suggest that the phaseout of ODS by the Montreal Protocol, and the recovery of stratospheric ozone, will act to decrease the SMB over the 21st century and the mitigation of sea-level rise. Read more
Earth Girl Volcano: characterizing and conveying volcanic hazard complexity in an interactive casual game of disaster preparedness and response Geoscience Communication DOI 10.5194/gc-3-343-2020 17 December 2020 Earth Girl Volcano is a casual strategy interactive game about saving communities at risk of volcanic hazards. The easy-to-play game features a friendly animated visual style and an engaging simulation of volcanic events. The game was designed by a multidisciplinary team to appeal to mainstream non-technical audiences, and it was inspired by the experiences of disaster survivors and civil defense teams. Players can learn through gameplay about disaster preparedness and response. Read more
The baseline wander correction based on the improved ensemble empirical mode decomposition (EEMD) algorithm for groundedelectrical source airborne transient electromagnetic signals Geoscientific Instrumentation, Methods and Data Systems DOI 10.5194/gi-9-443-2020 16 December 2020 The baseline wander has special characteristics, such as being low frequency, large amplitude, non-periodic, and non-stationary. It is caused by the receiving coil motion and always exists in the process of data acquisition. The proposed method can be used to solve similar problems. This paper has the following highlights: (1) the method can be used to process non-periodic and non-stationary signals; (2) the method is adaptive to satisfy the stopping criterion based on the measured signal. Read more
Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190–135 ka) Climate of the Past DOI 10.5194/cp-16-2203-2020 15 December 2020 We reconstruct atmospheric CO 2 from the EPICA Dome C ice core during Marine Isotope Stage 6 (185–135 ka) to understand carbon mechanisms under the different boundary conditions of the climate system. The amplitude of CO 2 is highly determined by the Northern Hemisphere stadial duration. Carbon dioxide maxima show different lags with respect to the corresponding abrupt CH 4 jumps, the latter reflecting rapid warming in the Northern Hemisphere. Read more
Reduced global warming from CMIP6 projections when weighting models by performance and independence Earth System Dynamics DOI 10.5194/esd-11-995-2020 14 December 2020 In this study, we weight climate models by their performance with respect to simulating aspects of historical climate and their degree of interdependence. Our method is found to increase projection skill and to correct for structurally similar models. The weighted end-of-century mean warming (2081–2100 relative to 1995–2014) is 3.7 °C with a likely (66 %) range of 3.1 to 4.6 °C for the strong climate change scenario SSP5-8.5; this is a reduction of 0.4 °C compared with the unweighted mean. Read more
European daily precipitation according to EURO-CORDEX regionalclimate models (RCMs) andhigh-resolution globalclimate models (GCMs) from the High-Resolution Model Intercomparison Project (HighResMIP) Geoscientific Model Development DOI 10.5194/gmd-13-5485-2020 11 December 2020 Now that global climate models (GCMs) can run at similar resolutions to regional climate models (RCMs), one may wonder whether GCMs and RCMs provide similar regional climate information. We perform an evaluation for daily precipitation distribution in PRIMAVERA GCMs (25–50 km resolution) and CORDEX RCMs (12–50 km resolution) over Europe. We show that PRIMAVERA and CORDEX simulate similar distributions. Considering both datasets at such a resolution results in large benefits for impact studies. Read more
Validation of Aeolus wind products above the Atlantic Ocean Atmospheric Measurement Techniques DOI 10.5194/amt-13-6007-2020 10 December 2020 A first validation for the European satellite Aeolus is presented. Aeolus is the first satellite that can actively measure horizontal wind profiles from space. Radiosonde launches on board the German research vessel Polarstern have been utilized to validate Aeolus observations over the Atlantic Ocean, a region where almost no other reference measurements are available. It is shown that Aeolus is able to measure accurately atmospheric winds and thus may significantly improve weather forecasts. Read more
Review article: Geothermal heat flow in Antarctica: current and future directions The Cryosphere DOI 10.5194/tc-14-3843-2020 9 December 2020 The Antarctic ice sheet is the largest source for sea level rise. However, one key control on ice sheet flow remains poorly constrained: the effect of heat from the rocks beneath the ice sheet (known as geothermal heat flow). Although this may not seem like a lot of heat, beneath thick, slow ice this heat can control how well the ice flows and can lead to melting of the ice sheet. We discuss the methods used to estimate this heat, compile existing data, and recommend future research. Read more
Soil: the great connector of our lives now and beyond COVID-19 SOIL DOI 10.5194/soil-6-541-2020 8 December 2020 Humanity depends on the existence of healthy soils, both for the production of food and for ensuring a healthy, biodiverse environment. In the face of global crises like the COVID-19 pandemic, a sustainable soil management strategy is essential to ensure food security based on more diverse, locally oriented, and resilient food production systems through improving access to land, sound land use planning, sustainable soil management, enhanced research, and investment in education and extension. Read more
The pulse of a montane ecosystem: coupling between daily cycles in solar flux, snowmelt, transpiration, groundwater, and streamflow at Sagehen Creek and Independence Creek, Sierra Nevada, USA Hydrology and Earth System Sciences DOI 10.5194/hess-24-5095-2020 7 December 2020 Streams and groundwaters often show daily cycles in response to snowmelt and evapotranspiration. These typically have a roughly 6 h time lag, which is often interpreted as a travel-time lag. Here we show that it is instead primarily a phase lag that arises because aquifers integrate their inputs over time. We further show how these cycles shift seasonally, mirroring the springtime retreat of snow cover to higher elevations and the seasonal advance and retreat of photosynthetic activity. Read more
Long-term historical trends in air pollutant emissions in Asia: Regional Emission inventory in ASia (REAS) version 3 Atmospheric Chemistry and Physics DOI 10.5194/acp-20-12761-2020 4 December 2020 A long historical emission inventory of major air pollutants in Asia during 1950–2015 was developed as Regional Emission inventory in ASia version 3 (REASv3). Trends of emissions and changes in source contributions in countries and regions in Asia during these 6 decades were analyzed. REASv3 provides monthly gridded data with 0.25° by 0.25° resolution for major source categories as well as table of emissions by countries and sub-regions for major sectors and fuel types. Read more
The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity Climate of the Past DOI 10.5194/cp-16-2095-2020 3 December 2020 The large-scale features of middle Pliocene climate from the 16 models of PlioMIP Phase 2 are presented. The PlioMIP2 ensemble average was ~ 3.2 °C warmer and experienced ~ 7 % more precipitation than the pre-industrial era, although there are large regional variations. PlioMIP2 broadly agrees with a new proxy dataset of Pliocene sea surface temperatures. Combining PlioMIP2 and proxy data suggests that a doubling of atmospheric CO 2 would increase globally averaged temperature by 2.6–4.8 °C. Read more
Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017 Atmospheric Chemistry and Physics DOI 10.5194/acp-20-12697-2020 2 December 2020 Airborne measurements of highly aged biomass burning aerosols (BBAs) over the remote southeast Atlantic provide unique aerosol parameters for climate models. Our observations demonstrate the persistence of strongly absorbing BBAs across wide regions of the South Atlantic. We also found significant vertical variation in the single-scattering albedo of these BBAs, as a function of relative chemical composition and size. Aerosol properties in the marine BL are suggested to be separated from the FT. Read more
A microphysics guide to cirrus – Part 2:Climatologies of clouds and humidity from observations Atmospheric Chemistry and Physics DOI 10.5194/acp-20-12569-2020 1 December 2020 To improve the representations of cirrus clouds in climate predictions, extended knowledge of their properties and geographical distribution is required. This study presents extensive airborne in situ and satellite remote sensing climatologies of cirrus and humidity, which serve as a guide to cirrus clouds. Further, exemplary radiative characteristics of cirrus types and also in situ observations of tropical tropopause layer cirrus and humidity in the Asian monsoon anticyclone are shown. Read more
The Aarhus Chamber Campaign on Highly Oxygenated Organic Molecules andAerosols (ACCHA): particle formation, organic acids, and dimer esters fromα-pinene ozonolysis at different temperatures Atmospheric Chemistry and Physics DOI 10.5194/acp-20-12549-2020 30 November 2020 Atmospheric particles are important in relation to human health and the global climate. As the global temperature changes, so may the atmospheric chemistry controlling the formation of particles from reactions of naturally emitted volatile organic compounds (VOCs). In the current work, we show how temperatures influence the formation and chemical composition of atmospheric particles from α-pinene: a biogenic VOC largely emitted in high-latitude environments such as the boreal forests. Read more