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Biogeosciences

Contrasting biosphere responses to hydrometeorological extremes: revisiting the 2010 western Russian heatwave

Northern forests enhanced their productivity during and before the 2010 Russian mega heatwave. We scrutinize this issue with a novel type of multivariate extreme event detection approach. Forests compensate for 54 % of the carbon losses in agricultural ecosystems due to vulnerable conditions in spring and better water management in summer. The findings highlight the importance of forests in mitigating climate change, while not alleviating the consequences of extreme events for food security.

Hydrology and Earth System Sciences

The importance of small artificial water bodies as sources of methane emissions in Queensland, Australia

Artificial water bodies are a major source of methane and an important contributor to flooded land greenhouse gas emissions. Past studies focussed on large water supply or hydropower reservoirs with small artificial water bodies (ponds) almost completely ignored. This regional study demonstrated ponds accounted for one-third of flooded land surface area and emitted over 1.6 million t CO₂eq. yr⁻¹(10 % of land use sector emissions). Ponds should be included in regional GHG inventories.

Earth System Dynamics

The climate of a retrograde rotating Earth

Model experiments show that changing the sense of Earth’s rotation has relatively little impact on the globally and zonally averaged energy budgets but leads to large shifts in continental climates and patterns of precipitation. The retrograde world is greener as the desert area shrinks. Deep water formation shifts from the North Atlantic to the North Pacific with subsequent changes in ocean overturning. Over large areas of the Indian Ocean, cyanobacteria dominate over bulk phytoplankton.

Solid Earth

GHOST: Geoscientific Hollow Sphere Tessellation

Solid Earth
DOI 10.5194/se-9-1169-2018
10 October 2018

I present the GHOST (Geoscientific Hollow Sphere Tessellation) software which allows for the fast generation of computational meshes in hollow sphere geometries counting up to a hundred million cells. Each mesh is composed of concentric spherical shells made of quadrilaterals or triangles. I focus here on three commonly used meshes used in the geodynamics/geophysics community and further benchmark the gravity and gravitational potential procedures in the simple case of a constant density.

Geoscience Communication

Building a Raspberry Pi school magnetometer network in the UK

As computing and geophysical sensor components have become increasingly affordable over the past decade, it is now possible to build a cost-effective system for monitoring the Earth’s natural magnetic field variations, in particular for space weather events, e.g. aurorae. Sensors available to the general public are ~ 100 times less sensitive than scientific instruments but only 1/100th of the price. We demonstrate a system that allows schools to contribute to a genuine scientific sensor network.

Atmospheric Measurement Techniques

Mapping carbon monoxide pollution from space down to city scales with daily global coverage

On 13 October 2017, the S5-P satellite was launched with TROPOMI as its only payload. One of the primary products is atmospheric CO observed with daily global coverage and spatial resolution of 7 × 7 km². The new dataset allows the sensing of CO enhancements above cities and industrial areas and can track pollution transport from biomass burning regions. Through validation with ground-based TCCON measurements we show that the CO data product is already well within the mission requirement.

Atmospheric Chemistry and Physics

Ice crystal number concentration estimates from lidar–radar satellite remote sensing – Part 1: Method and evaluation

The number concentration of ice crystals (N_i) is a key cloud property that remains very uncertain due to difficulties in determining it using satellites. This lack of global observational constraints limits our ability to constrain this property in models responsible for predicting future climate. This pair of papers fills this gap by showing and analyzing the first rigorously evaluated global climatology of N_i, leading to new information shedding light on the processes that control high clouds.

Biogeosciences

Reviews and syntheses: Carbon use efficiency from organisms to ecosystems – definitions, theories, and empirical evidence

Carbon fixed by plants and phytoplankton through photosynthesis is ultimately stored in soils and sediments or released to the atmosphere during decomposition of dead biomass. Carbon-use efficiency is a useful metric to quantify the fate of carbon – higher efficiency means higher storage and lower release to the atmosphere. Here we summarize many definitions of carbon-use efficiency and study how this metric changes from organisms to ecosystems and from terrestrial to aquatic environments.

Hydrology and Earth System Sciences

Why has catchment evaporation increased in the past 40 years? A data-based study in Austria

We analyze changes in catchment evaporation estimated from the water balances of 156 catchments in Austria over 1977–2014, as well as the possible causes of these changes. Our results show that catchment evaporation increased on average by 29 ± 14 mm yr⁻¹ decade⁻¹. We attribute this increase to changes in atmospheric demand (based on reference and pan evaporation), changes in vegetation (quantified by a satellite-based vegetation index), and changes in precipitation.

Atmospheric Chemistry and Physics

Trends in China’s anthropogenic emissions since 2010 as the consequence of clean air actions

To tackle the problem of severe air pollution, China has implemented active clean air policies in recent years. We quantified China’s anthropogenic emissions during 2010–2017 and identified the major driving forces of these trends by using a combination of bottom-up emission inventory and index decomposition analysis (IDA) approaches. The major air pollutants have reduced their emissions by 17–62 % during 2010–2017. The IDA results suggest that emission control measures are the main drivers.

Biogeosciences

Potential for phenol biodegradation in cloud waters

Biogeosciences
DOI 10.5194/bg-15-5733-2018
28 September 2018

The main objective of this work was to evaluate the potential degradation of phenol, a highly toxic pollutant, by cloud microorganisms. Phenol concentrations measured on five cloud samples collected at the PUY station in France were from 0.15 to 0.74 µg L⁻¹. Metatranscriptomic analysis suggested that phenol could be biodegraded directly in clouds, likely by Gammaproteobacteria. A large screening showed that 93 % of 145 bacterial strains isolated from clouds were able to degrade phenol.

Atmospheric Chemistry and Physics

How well do stratospheric reanalyses reproduce high-resolution satellite temperature measurements?

Reanalyses (RAs) are models which assimilate observations and are widely used as proxies for the true atmospheric state. Here, we resample six leading RAs using the weighting functions of four high-res satellite instruments, allowing a like-for-like comparison. We find that the RAs generally reproduce the satellite data well, except at high altitudes and in the tropics. However, we also find that the RAs more tightly correlate with each other than with observations, even those they assimilate.

Hydrology and Earth System Sciences

Global 5 km resolution estimates of secondary evaporation including irrigation through satellite data assimilation

Evaporation from wetlands, lakes and irrigation areas needs to be measured to understand water scarcity. So far, this has only been possible for small regions. Here, we develop a solution that can be applied at a very high resolution globally by making use of satellite observations. Our results show that 16% of global water resources evaporate before reaching the ocean, mostly from surface water. Irrigation water use is less than 1% globally but is a very large water user in several dry basins.

Ocean Science

World Ocean Circulation Experiment – Argo Global Hydrographic Climatology

Ocean Science
DOI 10.5194/os-14-1127-2018
27 September 2018

The new gridded WOCE-Argo Global Hydrographic Climatology (WAGHC) is described and compared with the NOAA WOA13 atlas. The monthly fields of temperature and salinity for 65 depth levels have a 1/4° spatial resolution. Two versions of the climatology were produced and differ with respect to the spatial interpolation performed on isobaric or isopycnal surfaces, respectively. The climatology characterizes the thermohaline state of the world ocean for the time period from 2008 to 2012.

Atmospheric Measurement Techniques

Cleaning up our water: reducing interferences from nonhomogeneous freezing of “pure” water in droplet freezing assays of ice-nucleating particles

Ice nucleation commonly studied using droplet freezing measurements suffers from artifacts caused by water impurities or substrate effects. We evaluate a series of substrates and water sources to find methods that reduce the background freezing temperature limit. The best performance was obtained from our new microfluidic device and hydrophobic glass surfaces, using filtered HPLC bottled water. We conclude with recommendations for best practices in droplet freezing experiments and data analysis.

Earth System Dynamics

Diurnal land surface energy balance partitioning estimated from the thermodynamic limit of a cold heat engine

Turbulent fluxes represent an efficient way to transport heat and moisture from the surface into the atmosphere. Due to their inherently highly complex nature, they are commonly described by semiempirical relationships. What we show here is that these fluxes can also be predicted by viewing them as the outcome of a heat engine that operates between the warm surface and the cooler atmosphere and that works at its limit.

The Cryosphere

Stopping the flood: could we use targeted geoengineering to mitigate sea level rise?

The Cryosphere
DOI 10.5194/tc-12-2955-2018
20 September 2018

In this paper, we explore the possibility of using locally targeted geoengineering to slow the rate of an ice sheet collapse. We find that an intervention as big as existing large civil engineering projects could have a 30 % probability of stopping an ice sheet collapse, while larger interventions have better odds of success. With more research to improve upon the simple designs we considered, it may be possible to perfect a design that was both achievable and had good odds of success.

Biogeosciences

Tracing water masses with ¹²⁹I and ²³⁶U in the subpolar North Atlantic along the GEOTRACES GA01 section

Biogeosciences
DOI 10.5194/bg-15-5545-2018
18 September 2018

The investigation of water mass transport pathways and timescales is important to understand the global ocean circulation. Following earlier studies, we use artificial radionuclides introduced to the oceans in the 1950s to investigate the water transport in the subpolar North Atlantic (SPNA). For the first time, we combine measurements of the long-lived iodine-129 and uranium-236 to confirm earlier findings/hypotheses and to better understand shallow and deep ventilation processes in the SPNA.

Geoscientific Model Development

sympl (v. 0.4.0) and climt (v. 0.15.3) – towards a flexible framework for building model hierarchies in Python

In the same way that the fruit fly or the yeast cell serve as model systems in biology, climate scientists use a range of computer models to gain a fundamental understanding of our climate system. These models range from extremely simple models that can run on your phone to those that require supercomputers. Sympl and climt are packages that make it easy for climate scientists to build a hierarchy of such models using Python, which facilitates easy to read and self-documenting models.

Hydrology and Earth System Sciences

Speculations on the application of foliar ¹³C discrimination to reveal groundwater dependency of vegetation and provide estimates of root depth and rates of groundwater use

Groundwater is a significant water resource for humans and for groundwater-dependent vegetation. Several challenges to managing both groundwater resources and dependent vegetation include defining the location of dependent vegetation, the rate of groundwater use, and the depth of roots accessing groundwater. In this study we demonstrate a novel application of measurements of stable isotopes of carbon that can be used to identify the location, the rooting depth, and the rate of groundwater use.

Atmospheric Chemistry and Physics

Inverse modelling of CF₄ and NF₃ emissions in East Asia

Emissions of carbon tetrafluoride CF₄, NF₃ and CHF₃ in east Asia have been calculated using atmospheric measurements and an atmospheric transport model. We calculate emissions of CF₄ to be quite constant between the years 2008 and 2015 for both China and South Korea, with 2015 emissions calculated at 4.33 ± 2.65 Gg yr^-1 and 0.36 ± 0.11 Gg yr^-1, respectively. Emission estimates of NF₃ from South Korea could be made with relatively small uncertainty at 0.6 ± 0.07 Gg yr^-1 in 2015.

Atmospheric Chemistry and Physics

The climate effects of increasing ocean albedo: an idealized representation of solar geoengineering

Marine cloud brightening has been proposed as a means of geoengineering/climate intervention, or deliberately altering the climate system to offset anthropogenic climate change. In idealized simulations that highlight contrasts between land and ocean, we find that the globe warms, including the ocean due to transport of heat from land. This study reinforces that no net energy input into the Earth system does not mean that temperature will necessarily remain unchanged.

Climate of the Past

Wet avalanches: long-term evolution in the Western Alps under climate and human forcing

In the context of a warming climate, mountain environments are especially vulnerable to a change in the risk pattern. Our study focuses on the past evolution of wet avalanches, likely triggered by warmer temperatures destabilizing the snow cover. In the last 3300 years we observed an increase of wet avalanche occurrence related to human activities, intensifying pressure on forest cover, as well as favorable climate conditions such as warmer temperatures coinciding with retreating glacier phases.

The Cryosphere

Mechanisms leading to the 2016 giant twin glacier collapses, Aru Range, Tibet

In Tibet, two glaciers suddenly collapsed in summer 2016 and produced two gigantic ice avalanches, killing nine people. This kind of phenomenon is extremely rare. By combining a detailed modelling study and high-resolution satellite observations, we show that the event was triggered by an increasing meltwater supply in the fine-grained material underneath the two glaciers. Contrary to what is often thought, this event is not linked to a change in the thermal condition at the glacier base.

Biogeosciences

Integrated management of a Swiss cropland is not sufficient to preserve its soil carbon pool in the long term

It is of great interest to know whether croplands act as a net source or sink of atmospheric CO₂and if soil carbon © stocks are preserved over long timescales due to the role of C in soil fertility. For a cropland in Switzerland it was found that managing the field under the Swiss framework of the Proof of Ecological Performance (PEP) resulted in soil C losses of 18.0 %. Additional efforts are needed to bring Swiss management practices closer to the goal of preserving soil C in the long term.

Ocean Science

Technical note: Two types of absolute dynamic ocean topography

Ocean Science
DOI 10.5194/os-14-947-2018
4 September 2018

Two types of marine geoid exist with the first type being the average level of sea surface height if the water is at rest (classical definition), and the second type being satellite-determined with the condition that the water is usually not at rest. The associated absolute dynamic ocean topography (DOT) also has two types. Horizontal gradients of the two DOTs are different with the 1st (2nd) type representing the absolute (relative) surface geostrophic currents.

Atmospheric Chemistry and Physics

Radiative feedbacks of dust in snow over eastern Asia in CAM4-BAM

This study extends our previous investigation in dust–radiation interactions to investigate SRF and its feedbacks on the regional climate and the dust cycle over east Asia by use of the CAM4-BAM. Our results show that SRF increases the east Asian dust emissions significantly by 13.7 % in the spring, in contrast to −7.6 % of decreased dust emissions by DRF. Hence, a significant feature of SRF on the Tibetan Plateau can create a positive feedback loop to enhance the dust cycle over east Asia.

The Cryosphere

Promising Oldest Ice sites in East Antarctica based on thermodynamical modelling

Our paper provides an important review of the state of knowledge for oldest-ice prospection, but also adds new basal geothermal heat flux constraints from recently acquired high-definition radar data sets. This is the first paper to contrast the two primary target regions for oldest ice: Dome C and Dome Fuji. Moreover, we provide statistical comparisons of all available data sets and a summary of the community’s criteria for the retrieval of interpretable oldest ice since the 2013 effort.

Geoscientific Model Development

The Variable Infiltration Capacity model version 5 (VIC-5): infrastructure improvements for new applications and reproducibility

Variable Infiltration Capacity (VIC) is a widely used hydrologic model. This paper documents the development of VIC version 5, which includes a reconfiguration of the model source code to support a wider range of modeling applications. It also represents a significant step forward for the VIC user community in terms of support for a range of modeling applications, reproducibility, and scientific robustness.

Earth System Dynamics

Varying soil moisture–atmosphere feedbacks explain divergent temperature extremes and precipitation projections in central Europe

Climate change projections of temperature extremes are particularly uncertain in central Europe. We demonstrate that varying soil moisture–atmosphere feedbacks in current climate models leads to an enhancement of model differences; thus, they can explain the large uncertainties in extreme temperature projections. Using an observation-based constraint, we show that the strong drying and large increase in temperatures exhibited by models on the hottest day in central Europe are highly unlikely.

Earth System Dynamics

The point of no return for climate action: effects of climate uncertainty and risk tolerance

We determine the point of no return (PNR) for climate change, which is the latest year to take action to reduce greenhouse gases to stay, with a certain probability, within thresholds set by the Paris Agreement. For a 67 % probability and a 2 K threshold, the PNR is the year 2035 when the share of renewable energy rises by 2 % per year. We show the impact on the PNR of the speed by which emissions are cut, the risk tolerance, climate uncertainties and the potential for negative emissions.

Annales Geophysicae

Sporadic auroras near the geomagnetic equator: in the Philippines, on 27 October 1856

A record has been found of an “aurora” observed on 27 October 1856 in the Philippines, practically at the magnetic equator. An analysis of this report indicates that it could belong to a “sporadic aurora” because of low magnetic activity at that time. We provide a possible physical mechanism that could explain the appearance of this sporadic, low-latitude aurora, according to the analyses on the observational report and magnetic observations at that time.

Earth System Dynamics

Population exposure to droughts in China under the 1.5 ºC global warming target

Results show that an additional 6.97 million people will be exposed to droughts in China under a 1.5 ºC target relative to reference period, mostly in the east of China. Demographic change is the primary contributor to exposure. Moderate droughts contribute the most to exposure among 3 grades of drought. Our simulations suggest that drought impact on people will continue to be a large threat to China under the 1.5 ºC target. It will be helpful in guiding adaptation and mitigation strategies.

Atmospheric Chemistry and Physics

Connecting regional aerosol emissions reductions to local and remote precipitation responses

Small particles in Earth’s atmosphere (also referred to as atmospheric aerosols) emitted by human activities impact Earth’s climate in complex ways and play an important role in Earth’s water cycle. We use a climate modeling approach and find that aerosols from the United States and Europe can have substantial effects on rainfall in far-away regions such as Africa’s Sahel or the Mediterranean. Air pollution controls in these regions may help reduce the likelihood and severity of Sahel drought.

Ocean Science

Overflow of cold water across the Iceland–Faroe Ridge through the Western Valley

The Western Valley is one of the passages across the Iceland–Scotland Ridge through which a strong overflow of cold, dense water has been thought to feed the deep limb of the Atlantic Meridional Overturning Circulation (AMOC), but its strength has not been known. Based on a field experiment with instruments moored across the valley, we show that this overflow branch is much weaker than previously thought and that this is because it is suppressed by the warm countercurrent in the upper layers.

Natural Hazards and Earth System Sciences

Global fatal landslide occurrence from 2004 to 2016

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-18-2161-2018
23 August 2018

Landslides are a hazard in terrestrial environments with slopes. This paper presents global analysis on patterns of fatal landsliding between 2004 and 2016, using a database collated from media reporting. The data show ~ 56 000 people were killed in 4862 landslide events. Active landslide years coincide with patterns of regional rainfall: most landslides were rainfall triggered. For the first time, analysis shows the number of landslides triggered by human activity increased with time.

Biogeosciences

Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution

During a French cruise in the northern North Atlantic Ocean in 2014, seawater samples were collected for dissolved Pb and Pb isotope analysis. Lead concentrations were highest in subsurface water flowing out of the Mediterranean Sea. The recently formed Labrador Sea Water (LSW) is much lower in Pb concentration than older LSW found in the West European Basin. Comparison of North Atlantic data from 1981 to 2014 shows decreasing Pb concentrations down to ~ 2500 m depth.

Hydrology and Earth System Sciences

Estimating time-dependent vegetation biases in the SMAP soil moisture product

Satellite soil moisture products can provide critical information on incipient droughts and the interplay between vegetation and water availability. However, time-variant systematic errors in the soil moisture products may impede their usefulness. Using a novel statistical approach, we detect such errors (associated with changing vegetation) in the SMAP soil moisture product. The vegetation-associated biases impede drought detection and the quantification of vegetation–water interactions.

Earth System Dynamics

Improving the representation of anthropogenic CO₂ emissions in climate models: impact of a new parameterization for the Community Earth System Model (CESM)

Earth system models provide simplified accounts of human–Earth interactions. Most current models treat CO₂ emissions as a homogeneously distributed forcing. However, this paper presents a new parameterization, POPEM (POpulation Parameterization for Earth Models), that computes anthropogenic CO₂ emissions at a grid point scale. A major advantage of this approach is the increased capacity to understand the potential effects of localized pollutant emissions on long-term global climate statistics.

Geoscientific Model Development

Developing a global operational seasonal hydro-meteorological forecasting system: GloFAS-Seasonal v1.0

Global overviews of upcoming flood and drought events are key for many applications from agriculture to disaster risk reduction. Seasonal forecasts are designed to provide early indications of such events weeks or even months in advance. This paper introduces GloFAS-Seasonal, the first operational global-scale seasonal hydro-meteorological forecasting system producing openly available forecasts of high and low river flow out to 4 months ahead.

Climate of the Past

Climate impact on the development of Pre-Classic Maya civilisation

We present two new palaeoclimatic records for the central Maya lowlands, adding valuable new insights to the impact of climate change on the development of Maya civilisation. Lake Tuspan’s diatom record is indicative of precipitation changes at a local scale, while a beach ridge elevation record from the world’s largest late Holocene beach ridge plain provides a regional picture.

Atmospheric Chemistry and Physics

Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe on 21–22 August 2017

Extremely large light extinction coefficients of 500 Mm^-1, about 20 times higher than after the Pinatubo volcanic eruptions in 1991, were observed by EARLINET lidars in the stratosphere over central Europe from 21 to 22 August, 2017. This paper provides an overview based on ground-based (lidar, AERONET) and satellite (MODIS, OMI) remote sensing.

Earth System Dynamics

A quantitative approach to evaluating the GWP timescale through implicit discount rates

The 100-year GWP is the most widely used metric for comparing the climate impact of different gases such as methane and carbon dioxide. However, there have been recent arguments for the use of different timescales. This paper uses straightforward estimates of future damages to quantitatively determine the appropriate timescale as a function of how society discounts the future and finds that the 100-year timescale is consistent with commonly used discount rates.

Biogeosciences

Ideas and perspectives: Strengthening the biogeosciences in environmental research networks

As knowledge in biology and geology explodes, science becomes increasingly specialised. Given the overlap of the environmental sciences, however, the explosion in knowledge inevitably creates opportunities for interconnecting the biogeosciences. Here, 30 scientists emphasise the opportunities for biogeoscience collaborations across the world’s remarkable long-term environmental research networks that can advance science and engage larger scientific and public audiences.

The Cryosphere

Channelized, distributed, and disconnected: subglacial drainage under a valley glacier in the Yukon

We analyse a large glacier borehole pressure dataset and provide a holistic view of the observations, suggesting a consistent picture of the evolution of the subglacial drainage system. Some aspects are consistent with the established understanding and others ones are not. We propose that most of the inconsistencies arise from the capacity of some areas of the bed to become hydraulically isolated. We present an adaptation of an existing drainage model that incorporates this phenomena.

Atmospheric Chemistry and Physics

Formation and evolution of tar balls from northwestern US wildfires

This paper presents the first direct atmospheric observations of the formation and evolution of tar balls (TBs) in forest fires collected during the Department of Energy’s Biomass Burning Observation Project (BBOP). We quantify, for the first time, the TB mass fraction in the BB plumes and show that this mass fraction increases from less than 1 % to 50 % within the first couple of hours of plume aging. Using Mie theory we find that TBs are consistent with being weak light absorbers.

Climate of the Past

Testing the consistency between changes in simulated climate and Alpine glacier length over the past millennium

Glaciers provide iconic illustrations of past climate change, but records of glacier length fluctuations have not been used systematically to test the ability of models to reproduce past changes. One reason is that glacier length depends on several complex factors and so cannot be simply linked to the climate simulated by models. This is done here, and it is shown that the observed glacier length fluctuations are generally well within the range of the simulations.

Annales Geophysicae

The mirror mode: a “superconducting” space plasma analogue

The physics of the magnetic mirror mode in its final state of saturation, the thermodynamic equilibrium, is re-examined to demonstrate that the mirror mode is the classical analogue of a superconducting effect in an anisotropic-pressure space plasma. Three different spatial correlation scales are identified which control the behaviour of its evolution into large-amplitude chains of mirror bubbles.

Earth System Dynamics

Using network theory and machine learning to predict El Niño

The prediction of the El Niño phenomenon, an increased sea surface temperature in the eastern Pacific, fascinates people for a long time. El Niño is associated with natural disasters, such as droughts and floods. Current methods can make a reliable prediction of this phenomenon up to 6 months ahead. However, this article presents a method which combines network theory and machine learning which predicts El Niño up to 1 year ahead.

Atmospheric Chemistry and Physics

HTAP2 multi-model estimates of premature human mortality due to intercontinental transport of air pollution and emission sectors

Emissions from one continent affect air quality and health elsewhere. Here we quantify the effects of intercontinental PM_2.5 and ozone transport on human health using a new multi-model ensemble, evaluating the health effects of emissions from six world regions and three emission source sectors. Emissions from one region have significant health impacts outside of that source region; similarly, foreign emissions contribute significantly to air-pollution-related deaths in several world regions.