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Earth System Dynamics

The role of prior assumptions in carbon budget calculations

Levels of future temperature change are often used interchangeably with carbon budget allowances in climate policy, a relatively robust relationship on the timescale of this century. However, recent advances in understanding underline that continued warming after net-zero emissions have been achieved cannot be ruled out by observations of warming to date. We consider here how such behavior could be constrained and how policy can be framed in the context of these uncertainties.

Natural Hazards and Earth System Sciences

Snow avalanche detection and mapping in multitemporal and multiorbital radar images from TerraSAR-X and Sentinel-1

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-20-1783-2020
2 July 2020

To assess snow avalanche mapping with radar satellites in Switzerland, we compare 2 m resolution TerraSAR-X images, 10 m resolution Sentinel-1 images, and optical 1.5 m resolution SPOT-6 images. We found that radar satellites provide a valuable option to map at least larger avalanches, though avalanches are mapped only partially. By combining multiple orbits and polarizations from S1, we achieved mapping results of quality almost comparable to single high-resolution TerraSAR-X images.

Geoscientific Model Development

Towards an objective assessment of climate multi-model ensembles – a casestudy: the Senegalo-Mauritanian upwelling region

The most robust representation of climate is usually obtained by averaging a large number of simulations, thereby cancelling individual model errors. Here, we work towards an objective way of selecting the least biased models over a certain region, based on physical parameters. This statistical method based on a neural classifier and multi-correspondence analysis is illustrated here for the Senegalo-Mauritanian region, but it could potentially be developed for any other region or process.

Atmospheric Chemistry and Physics

Modelling the potential impacts of the recent, unexpected increase in CFC-11 emissions on total column ozone recovery

The Montreal Protocol was agreed in 1987 to limit and then stop the production of man-made CFCs, which destroy stratospheric ozone. As a result, the atmospheric abundances of CFCs are now declining in the atmosphere. However, the atmospheric abundance of CFC-11 is not declining as expected under complete compliance with the Montreal Protocol. Using the UM-UKCA chemistry–climate model, we explore the impact of future unregulated production of CFC-11 on ozone recovery.

The Cryosphere

Changes of the Arctic marginal ice zone during the satellite era

It is well known that the Arctic sea ice extent is declining, and it is often assumed that the marginal ice zone (MIZ), the area of partial sea ice cover, is consequently increasing. However, we find no trend in the MIZ extent during the last 40 years from observations that is consistent with a widening of the MIZ as it moves northward. Differences of MIZ extent between different satellite retrievals are too large to provide a robust basis to verify model simulations of MIZ extent.

Biogeosciences

Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2

The Zero Emissions Commitment (ZEC) is the change in global temperature expected to occur following the complete cessation of CO ₂ emissions. Here we use 18 climate models to assess the value of ZEC. For our experiment we find that ZEC 50 years after emissions cease is between −0.36 to +0.29 °C. The most likely value of ZEC is assessed to be close to zero. However, substantial continued warming for decades or centuries following cessation of CO ₂ emission cannot be ruled out.

Geoscientific Model Development

RainNet v1.0: a convolutional neural network for radar-based precipitation nowcasting

In this study, we present RainNet, a deep convolutional neural network for radar-based precipitation nowcasting, which was trained to predict continuous precipitation intensities at a lead time of 5 min. RainNet significantly outperformed the benchmark models at all lead times up to 60 min. Yet, an undesirable property of RainNet predictions is the level of spatial smoothing. Obviously, RainNet learned an optimal level of smoothing to produce a nowcast at 5 min lead time.

Hydrology and Earth System Sciences

Changing global cropping patterns to minimize national blue water scarcity

Previous studies on water saving through food trade focussed either on comparing water productivities among countries or on analysing food trade in relation to national water endowments. Here, we consider, for the first time, both differences in water productivities and water endowments to analyse national comparative advantages. Our study reveals that blue water scarcity can be reduced to sustainable levels by changing cropping patterns while maintaining current levels of global production.

The Cryosphere

New observations of the distribution, morphology and dissolution dynamics of cryogenic gypsum in the Arctic Ocean

Based on an observed omnipresence of gypsum crystals, we concluded that their release from melting sea ice is a general feature in the Arctic Ocean. Individual gypsum crystals sank at more than 7000 m d ⁻¹ , suggesting that they are an important ballast mineral. Previous observations found gypsum inside phytoplankton aggregates at 2000 m depth, supporting gypsum as an important driver for pelagic-benthic coupling in the ice-covered Arctic Ocean.

Natural Hazards and Earth System Sciences

Induced seismicity risk analysis of the hydraulic stimulation of a geothermal well on Geldinganes, Iceland

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-20-1573-2020
16 June 2020

This study presents a first-of-its-kind pre-drilling probabilistic induced seismic risk analysis for the Geldinganes (Iceland) deep-hydraulic stimulation. The results of the assessment indicate that the individual risk within a radius of 2 km around the injection point is below the safety limits. However, the analysis is affected by a large variability due to the presence of pre-drilling deep uncertainties. This suggests the need for online risk updating during the stimulation.

Hydrology and Earth System Sciences

Linking economic and social factors to peak flows in an agricultural watershed using socio-hydrologic modeling

We describe a socio-hydrologic model that couples an agent-based model (ABM) of human decision-making with a hydrologic model. We establish this model for a typical agricultural watershed in Iowa, USA, and simulate the evolution of large discharge events over a 47-year period under changing land use. Using this modeling approach, relationships between seemingly unrelated variables such as crop markets or crop yields and local peak flow trends are quantified.

Hydrology and Earth System Sciences

Comparing Palmer Drought Severity Index drought assessments using the traditional offline approach with direct climate model outputs

Many previous studies using offline drought indices report that future warming will increase worldwide drought. However, this contradicts observations/projections of vegetation greening and increased runoff. We resolved this paradox by re-calculating the same drought indices using direct climate model outputs and find no increase in future drought as the climate warms. We also find that accounting for the impact of CO ₂ on plant transpiration avoids the previous overestimation of drought.

Atmospheric Measurement Techniques

N2O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

The latest commercial laser spectrometers have the potential to revolutionize N ₂ O isotope analysis. However, to do so, they must be able to produce trustworthy data. Here, we test the performance of widely used laser spectrometers for ambient air applications and identify instrument-specific dependencies on gas matrix and trace gas concentrations. We then provide a calibration workflow to facilitate the operation of these instruments in order to generate reproducible and accurate data.

Atmospheric Measurement Techniques

Model-based climatology of diurnal variability in stratospheric ozone as adata analysis tool

We use the NASA GEOS-GMI chemistry climate model to construct a climatology of stratospheric ozone diurnal variations as a function of latitude, pressure and month, which can be used in a variety of data analysis tasks involving ozone observations made at different times of the day. The climatology compares well with previous modeling simulations and available observations, and to the authors’ knowledge is the first characterization of the diurnal cycle available for general ozone data analyses.

Natural Hazards and Earth System Sciences

Present and future changes in winter climate indices relevant for access disruptions in Troms, northern Norway

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-20-1847-2020
9 June 2020

We have studied changes in winter weather known to trigger road closures and isolation of small seaside communities in northern Norway. We find that snow amounts and heavy snowfall events have increased in the past, while future projections for 2040–2100 show a decrease in snow-related indices. Events of heavy water supply and zero crossings are expected to increase. Our results imply fewer dry-snow-related access disruptions in the future, while wet-snow avalanches and slushflows may increase.

Atmospheric Measurement Techniques

Simultaneous measurements of the relative-humidity-dependent aerosol lightextinction, scattering, absorption, and single-scattering albedo with ahumidified cavity-enhanced albedometer

We report the first demonstration of a humidified cavity-enhanced albedometer (H-CEA) that combines a broadband cavity-enhanced aerosol albedometer with a humidigraph system for simultaneous and accurate measurements of multiple optical hygroscopic parameters ( f (RH)ext,scat,abs,ω) at λ = 532 nm. The instrument is suitable for operating under high RH-conditions and has sampling advantages over independent measurements of different parameters with different instruments.

Natural Hazards and Earth System Sciences

Network-risk: an open GIS toolbox for estimating the implications of transportation network damage due to natural hazards, tested for Bucharest, Romania

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-20-1421-2020
4 June 2020

Natural hazards have an increasing impact on transportation networks. In order to analyze it we developed Network-risk – an open toolbox for ArcGIS. The toolbox links input data such as network datasets (also OpenStreetMap – OSM – data), traffic values or segments which can be affected, determining the difficulty to reach an area and enabling evaluation of socioeconomic implications. By testing Network-risk for Bucharest we show areas difficult to reach by emergency units in earthquakes.

Nonlinear Processes in Geophysics

Effects of upwelling duration and phytoplankton growth regime on dissolved-oxygen levels in an idealized Iberian Peninsula upwelling system

The oceans are losing oxygen, and future changes may worsen this problem. We performed computer simulations of an idealized Iberian Peninsula upwelling system to identify the main fine-scale processes driving dissolved oxygen variability as well as study the response of oxygen levels to changes in wind patterns and phytoplankton species. Our results suggest that oxygen levels would decrease if the wind blows for long periods of time or if phytoplankton is dominated by species that grow slowly.

Atmospheric Chemistry and Physics

Exploration of oxidative chemistry and secondary organic aerosol formation in the Amazon during the wet season:explicit modeling of the Manaus urban plume with GECKO-A

The GoAmazon 2014/5 field campaign took place near the city of Manaus, Brazil, isolated in the Amazon rainforest, to study the impacts of urban pollution on natural air masses. We simulated this campaign with an extremely detailed organic chemistry model to understand how the city would affect the growth and composition of natural aerosol particles. Discrepancies between the model and the measurements indicate that the chemistry of naturally emitted organic compounds is still poorly understood.

Hydrology and Earth System Sciences

Wetropolis extreme rainfall and flood demonstrator: from mathematical design to outreach

Wetropolis is a table-top demonstration model with extreme rainfall and flooding, including random rainfall, river flow, flood plains, an upland reservoir, a porous moor, and a city which can flood. It lets the viewer experience extreme rainfall and flood events in a physical model on reduced spatial and temporal scales with an event return period of 6.06 min rather than, say, 200 years. We disseminate its mathematical design and how it has been shown most prominently to over 500 flood victims.

Geoscience Communication

Rapid collaborative knowledge building via Twitter after significantgeohazard events

Among social media platforms, Twitter is valued by scholars to disseminate scientific information. Using two 2018 geohazard events as examples, we show that collaborative open data sharing and discussion on Twitter promote very rapid building of knowledge. This breaks down the traditional ivory tower of academia, making science accessible to nonacademics who can follow the discussion. It also presents the opportunity for a new type of scientific approach within global virtual teams.

Atmospheric Measurement Techniques

Microwave and submillimeter wave scattering of oriented ice particles

Microwave dual-polarization observations consistently show that larger atmospheric ice particles tend to have a preferred orientation. We provide a publicly available database of microwave and submillimeter wave scattering properties of oriented ice particles based on discrete dipole approximation scattering calculations. Detailed radiative transfer simulations, recreating observed polarization patterns, are additionally presented in this study.

Atmospheric Chemistry and Physics

Dynamic projection of anthropogenic emissions in China: methodology and 2015–2050 emission pathways under a range of socio-economic, climate policy, and pollution control scenarios

Future trends in air pollution and greenhouse gas emissions in China are of great concern to the community. Here we developed a sophisticated dynamic projection model to understand 2015–2050 emission pathways under a range of socio-economic, climate policy, and pollution control scenarios. By coupling strong low-carbon transitions and clean air policy, emissions of major air pollutants in China will be reduced by 58–87 % during 2015–2050. This work can support future co-governance policy design.

Atmospheric Measurement Techniques

A machine-learning-based cloud detection and thermodynamic-phaseclassification algorithm using passive spectral observations

A machine-learning (ML)-based approach that can be used for cloud mask and phase detection is developed. An all-day model that uses infrared (IR) observations and a daytime model that uses shortwave and IR observations from a passive instrument are trained separately for different surface types. The training datasets are selected by using reference pixel types from collocated space lidar. The ML approach is validated carefully and the overall performance is better than traditional methods.

The Cryosphere

The catastrophic thermokarst lake drainage events of 2018 in northwestern Alaska: Fast-forward into the future

Northwestern Alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. In particular, the Baldwin and northern Seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage, like many other regions at the southern margins of continuous permafrost. We used Sentinel-1 synthetic aperture radar (SAR) and Planet CubeSat optical remote sensing data to analyze recently observed widespread lake drainage.

The Cryosphere

Quantification of seasonal and diurnal dynamics of subglacial channels using seismic observations on an Alpine glacier

Our study addresses key questions on the subglacial drainage system physics through a novel observational approach that overcomes traditional limitations. We conducted, over 2 years, measurements of the subglacial water-flow-induced seismic noise and of glacier basal sliding speeds. We then inverted for the subglacial channel’s hydraulic pressure gradient and hydraulic radius and investigated the links between the equilibrium state of subglacial channels and glacier basal sliding.

Biogeosciences

Summarizing the state of the terrestrial biosphere in few dimensions

To closely monitor the state of our planet, we require systems that can monitor
the observation of many different properties at the same time. We create
indicators that resemble the behavior of many different simultaneous
observations. We apply the method to create indicators representing the
Earth’s biosphere. The indicators show a productivity gradient and a water
gradient. The resulting indicators can detect a large number of changes and
extremes in the Earth system.

Atmospheric Measurement Techniques

Intercomparison of wind observations from the European Space Agency’s Aeolus satellite mission and the ALADIN Airborne Demonstrator

This work reports on the first airborne validation campaign of ESA’s Earth Explorer mission Aeolus, conducted in central Europe during the commissioning phase in November 2018. After presenting the methodology used to compare the data sets from the satellite, the airborne wind lidar and the ECWMF model, the wind results from the underflights performed are analyzed and discussed, providing a first assessment of the accuracy and precision of the preliminary Aeolus wind data.

Atmospheric Chemistry and Physics

The acidity of atmospheric particles and clouds

Acid rain is recognized for its impacts on human health and ecosystems, and programs to mitigate these effects have had implications for atmospheric acidity. Historical measurements indicate that cloud and fog droplet acidity has changed in recent decades in response to controls on emissions from human activity, while the limited trend data for suspended particles indicate acidity may be relatively constant. This review synthesizes knowledge on the acidity of atmospheric particles and clouds.

Earth Surface Dynamics

Drainage divide networks – Part 2: Response to perturbations

Drainage divides are believed to provide clues about divide migration and the instability of landscapes. Here, we present a novel approach to extract drainage divides from digital elevation models and to order them in a drainage divide network. We present our approach by studying natural and artificial landscapes generated with a landscape evolution model and disturbed to induce divide migration.

Geoscience Communication

The benefits to climate science of including early-career scientists asreviewers

Early-career scientists (ECSs) are rarely invited to act as peer reviewers. Participating in a group peer review of the IPCC Special Report on Ocean and Cryosphere in a Changing Climate, PhD students spent more time reviewing than more established scientists and provided a similar proportion of substantive comments. By soliciting and including ECSs in peer review, the scientific community would reduce the burden on more established scientists and may improve the quality of that process.

Nonlinear Processes in Geophysics

Brief communication: Residence time of energy in the atmosphere

We deduce that after a global thermal perturbation, the Earth’s
atmosphere would need about a couple of months to come back to equilibrium.

Earth Surface Dynamics

Drainage divide networks – Part 1: Identification and ordering in digital elevation models

Drainage divides are believed to provide clues about divide migration and the instability of landscapes. Here, we present a novel approach to extract drainage divides from digital elevation models and to order them in a drainage divide network. We present our approach by studying natural and artificial landscapes generated with a landscape evolution model and disturbed to induce divide migration.

Biogeosciences

Authigenic formation of Ca–Mg carbonates in the shallow alkaline LakeNeusiedl, Austria

Dolomite (CaMg(CO ₃ ) ₂ ) is supersaturated in many aquatic settings (e.g., seawater) on modern Earth but does not precipitate directly from the fluid, a fact known as the dolomite problem. The widely acknowledged concept of dolomite precipitation involves microbial extracellular polymeric substances (EPSs) and anoxic conditions as important drivers. In contrast, results from Lake Neusiedl support an alternative concept of Ca–Mg carbonate precipitation under aerobic and alkaline conditions.

Atmospheric Chemistry and Physics

Oxygen and sulfur mass-independent isotopic signatures in black crusts: thecomplementary negative Δ33S reservoir of sulfate aerosols?

Given their critical impact on radiative forcing, sulfate aerosols have been extensively studied using their isotope signatures (δ ³⁴ S, ∆ ³³ S, ∆ ³⁶ S, δ ¹⁸ O, and ∆ ¹⁷ O). A striking observation is that ∆ ³³ S > 0 ‰, implying a missing reservoir in the sulfur cycle. Here, we measured ∆ ³³ S < 0 ‰ in black crust sulfates (i.e., formed on carbonate walls) that must therefore result from distinct chemical pathway(s) compared to sulfate aerosols, and they may well represent this complementary reservoir.

Hydrology and Earth System Sciences

Surface water and groundwater: unifying conceptualization and quantification of the two “water worlds”

We present a blueprint for a unified modelling framework to quantify chemical transport in both surface water and groundwater systems. There has been extensive debate over recent decades, particularly in the surface water literature, about how to explain and account for long travel times of chemical species that are distinct from water flow (rainfall-runoff) travel times. We suggest a powerful modelling framework known to be robust and effective from the field of groundwater hydrology.

Earth System Dynamics

Statistical estimation of global surface temperature response to forcing under the assumption of temporal scaling

This paper presents efficient Bayesian methods for linear response models of global mean surface temperature that take into account long-range dependence. We apply the methods to the instrumental temperature record and historical model runs in the CMIP5 ensemble to provide estimates of the transient climate response and temperature projections under the Representative Concentration Pathways.

Atmospheric Chemistry and Physics

Technical note: Preparation and purification of atmospherically relevant α-hydroxynitrate esters of monoterpenes

This report describes a simple, safe and effective method to prepare nitrate esters of terpenes (carene, limonene, perillic alcohol, beta-pinene and alpha-pinene) which are key oxidation products in the atmosphere. These compounds are implicated in the formation of secondary organic aerosols. A compilation of the relevant spectroscopic data has been presented. The availability of these compounds and their characterization data will enable further study of the structure–reactivity relationships.

Natural Hazards and Earth System Sciences

Run-up, inundation, and sediment characteristics of the 22 December 2018 Sunda Strait tsunami, Indonesia

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-20-933-2020
21 April 2020

This article reports the results of a field survey carried out in the disaster area of the December 2018 Sunda Strait tsunami, Indonesia. It provides data covering run-up heights, inundations, tsunami directions, and sediment characteristics. The data can be used for the validation of hydrodynamic models, and they contribute to a better understanding of the Sunda Strait tsunami caused by the Anak Krakatau volcano. In addition, they are important for spatial planning and mitigation efforts.

Atmospheric Chemistry and Physics

Supercooled liquid water cloud observed, analysed, and modelled at the top ofthe planetary boundary layer above Dome C, Antarctica

Thin (~ 100 m) supercooled liquid water (SLW, water staying in liquid phase below 0 °C) clouds have been detected, analysed, and modelled over the Dome C (Concordia, Antarctica) station during the austral summer 2018–2019 using observations and meteorological analyses. The SLW clouds were observed at the top of the planetary boundary layer and the SLW content was always strongly underestimated by the model indicating an incorrect simulation of the surface energy budget of the Antarctic Plateau.

SOIL

Ramped thermal analysis for isolating biologically meaningful soil organic matter fractions with distinct residence times

SOIL
DOI 10.5194/soil-6-131-2020
16 April 2020

Soils contain one of the largest and most dynamic pools of carbon on Earth, yet scientists still struggle to understand the reactivity and fate of soil organic matter upon disturbance. In this study, we found that with increasing thermal stability, the turnover time of organic matter increased from decades to centuries with a concurrent shift in chemical composition. In this proof-of-concept study, we found that ramped thermal analyses can provide new insights for understanding soil carbon.

Nonlinear Processes in Geophysics

Baroclinic and barotropic instabilities in planetary atmospheres: energetics, equilibration and adjustment

Baroclinic and barotropic instabilities are well known as the processes responsible for the production of the most important energy-containing eddies in the atmospheres and oceans of Earth and other planets. Linear and nonlinear instability theories provide insights into when such instabilities may occur, grow to a large amplitude and saturate, with examples from the laboratory, simplified numerical models and planetary atmospheres. We conclude with a number of open issues for future research.

Atmospheric Chemistry and Physics

Description and Evaluation of the specified-dynamics experiment in the Chemistry-Climate Model Initiative

Atmospheric composition is strongly influenced by global-scale winds that are not always properly simulated in computer models. A common approach to correct for this bias is to relax or nudge to the observed winds. Here we systematically evaluate how well this technique performs across a large suite of chemistry–climate models in terms of its ability to reproduce key aspects of both the tropospheric and stratospheric circulations.

Atmospheric Measurement Techniques

Real-time pollen monitoring using digital holography

We present the first validation of the only operational automatic pollen monitoring system based on holography, the Swisens Poleno. The device produces real-time images of coarse aerosols, and by applying a machine learning algorithm we identify a range of pollen taxa with accuracy >90 %. The device was further validated in controlled chamber experiments to verify the counting ability and the performance of additional fluorescence measurements, which can further be used in pollen identification.

Atmospheric Chemistry and Physics

Technical note: LIMS observations of lower stratospheric ozone in the southern polar springtime of 1978

The Nimbus 7 limb infrared monitor of the stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. This note focuses on the lower stratosphere of the southern hemisphere, subpolar regions in relation to the position of the polar vortex. Both LIMS ozone and nitric acid show reductions within the edge of the polar vortex at 46 hPa near 60° S from late October through mid-November 1978, indicating that there was a chemical loss of Antarctic ozone some weeks earlier.

Climate of the Past

Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period

We investigate the changes in natural methane emissions between the Last Glacial Maximum and preindustrial periods with a methane-enabled version of MPI-ESM. We consider all natural sources of methane except for emissions from wild animals and geological sources. Changes are dominated by changes in tropical wetland emissions, high-latitude wetlands play a secondary role, and all other natural sources are of minor importance. We explain the changes in ice core methane by methane emissions only.

Atmospheric Chemistry and Physics

Methane emissions from the Munich Oktoberfest

We demonstrate for the first time that large festivals can be significant methane sources, though they are not included in emission inventories. We combined in situ measurements with a Gaussian plume model to determine the Oktoberfest emissions and show that they are not due solely to human biogenic emissions, but are instead primarily fossil fuel related. Our study provides the foundation to develop reduction policies for such events and new pathways to mitigate fossil fuel methane emissions.

Atmospheric Chemistry and Physics

Deconvolution of boundary layer depth and aerosol constraints on cloud water path in subtropical stratocumulus decks

Cloud water content and the number of droplets inside clouds covary with boundary layer depth. This covariation may amplify the change in water content due to a change in droplet number inferred from long-term observations. Taking this into account shows that the change in water content for increased droplet number in observations and high-resolution simulations agrees in shallow boundary layers. Meanwhile, deep boundary layers are under-sampled in process-scale simulations and observations.

Earth System Dynamics

Back to the future II: tidal evolution of four supercontinent scenarios

We have confirmed that there is a supertidal cycle associated with the supercontinent cycle. As continents drift due to plate tectonics, oceans also change size, controlling the strength of the tides and causing periods of supertides. In this work, we used a coupled tectonic–tidal model of Earth’s future to test four different scenarios that undergo different styles of ocean closure and periods of supertides. This has implications for the Earth system and for other planets with liquid oceans.

Biogeosciences

Scaling carbon fluxes from eddy covariance sites to globe: synthesis andevaluation of the FLUXCOM approach

We test the approach of producing global gridded carbon fluxes based on combining machine learning with local measurements, remote sensing and climate data. We show that we can reproduce seasonal variations in carbon assimilated by plants via photosynthesis and in ecosystem net carbon balance. The ecosystem’s mean carbon balance and carbon flux trends require cautious interpretation. The analysis paves the way for future improvements of the data-driven assessment of carbon fluxes.