EG - Encyclopedia topics

Humans affect the reflective properties (albedo) of Earth's surface and the amount of solar energy that it absorbs, in turn affecting climate. In recent years, a variety of climate metrics have been applied to characterize albedo perturbations in terms of their CO₂-equivalent effects, despite the lack of scientific consensus surrounding the methods behind them. We review these metrics, evaluate their (de)merits, provide guidance for future application, and suggest avenues for future research.

The scientific questions posed by the climate sciences are central to socioeconomic concerns today. This paper revisits several crucial questions, starting with What can we predict beyond 1 week, for how long, and by what methods?, and ending with Can we achieve enlightened climate control of our planet by the end of the century? We review the progress in dealing with the nonlinearity and stochasticity of the Earth system and emphasize major strides in coupled climate–economy modeling.

Removal efficiency of carbon and nitrogen in constructed wetlands is inconsistent and does not reveal whether the removal processes are from physical attenuation or transformation to other reactive forms. Previous research did not consider "pollution swapping" driven by transformational processes. Herein the biogeochemical dynamics and fate of carbon and nitrogen and their potential impact on the environment, as well as novel ways in which these knowledge gaps may be eliminated, are explored.

The Global Carbon Budget 2017 describes data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. It is the 12th annual update and the 6th published in this journal.

The Global Carbon Budget 2019 describes the data sets and methodology used to quantify the emissions of carbon dioxide and their partitioning among the atmosphere, land, and ocean. These living data are updated every year to provide the highest transparency and traceability in the reporting of CO₂, the key driver of climate change.

African natural ecosystems and agricultural lands are a significant source of GHG. However, there are huge research gaps and understanding of Africa's contribution to global GHG emissions remains highly uncertain. The strategy for addressing this data gap involves identifying priorities for data acquisition, utilizing appropriate technologies, and establishing networks and collaboration.

An accurate assessment of the methane budget is important to understand the atmospheric methane concentrations and trends and to provide realistic pathways for climate change mitigation. The various and diffuse sources of methane as well and its oxidation by a very short lifetime radical challenge this assessment. We quantify the methane sources and sinks as well as their uncertainties based on both bottom-up and top-down approaches provided by a broad international scientific community.

Qualitative evidence contained within historical sources provides an important record of climate variability for periods prior to the onset of systematic meteorological data collection. Before such evidence can be used for climate reconstructions, it needs to be converted to a quantitative format. A common approach is the generation of ordinal-scale climate indices. This review, written by members of the PAGES CRIAS working group, provides a global synthesis of the use of the index approach.

The Eocene–Oligocene transition was a major climate cooling event from a largely ice-free world to the first major glaciation of Antarctica, approximately 34 million years ago. This paper reviews observed changes in temperature, CO₂ and ice sheets from marine and land-based records at this time. We present a new model–data comparison of this transition and find that CO₂-forced cooling provides the best explanation of the observed global temperature changes.

Weather and climate models consist of complex software evolving in response to both scientific requirements and changing computing hardware. After years of relatively stable hardware, more diversity is arriving. It is possible that this hardware diversity and the pace of change may lead to an inability for modelling groups to manage their software development. This chasm between aspiration and reality may need to be bridged by large community efforts rather than traditional in-house efforts.

The development of coupled ocean atmosphere climate models is a complex process that inevitably includes multiple calibration steps (sometimes called tuning). Tuning uses degrees of freedom allowed by uncertainties in model approximations to modify parameters to make the simulation better align with some selected observed target(s). We describe how these tuning targets, parameters, and philosophy vary across six US modeling centers in order to increase the transparency of the practice.

We present a review of the make-up of 20 models participating in the Chemistry–Climate Model Initiative (CCMI). In comparison to earlier such activities, most of these models comprise a whole-atmosphere chemistry, and several of them include an interactive ocean module. This makes them suitable for studying the interactions of tropospheric air quality, stratospheric ozone, and climate. The paper lays the foundation for other studies using the CCMI simulations for scientific analysis.

The Paleoclimate Modelling Intercomparison Project (PMIP) takes advantage of the existence of past climate states radically different from the recent past to test climate models used for climate projections and to better understand these climates. This paper describes the PMIP contribution to CMIP6 (Coupled Model Intercomparison Project, 6th phase) and possible analyses based on PMIP results, as well as on other CMIP6 projects.

Atmospheric dynamical cores are a fundamental component of global atmospheric modeling systems and are responsible for capturing the dynamical behavior of the Earth's atmosphere. To better understand modern dynamical cores, this paper aims to provide a comprehensive review of 11 dynamical cores, drawn from modeling centers and groups that participated in the 2016 Dynamical Core Model Intercomparison Project (DCMIP) workshop and summer school.

This review article compiles the characteristics of the gas chlorine nitrate and discusses its role in atmospheric chemistry. Chlorine nitrate is a reservoir of both stratospheric chlorine and nitrogen. Formation and sink processes are discussed, as well as spectral features and spectroscopic studies. Remote sensing, fluorescence, and mass spectroscopic measurement techniques are introduced, and global distributions and the annual cycle are discussed in the context of chlorine de-/activation.

This study is topical and provides a state-of-the-art scientific overview of data availability from bottom-up and top-down CH₄ and N₂O emissions in the EU27 and UK. The data integrate recent emission inventories with process-based model data and regional/global inversions for the European domain, aiming at reconciling them with official country-level UNFCCC national GHG inventories in support to policy and to facilitate real-time verification procedures.

Methane (CH₄) emissions from the boreal–Arctic region are globally significant, but the current magnitude of annual emissions is not well defined. Here we present a dataset of surface CH₄ fluxes from northern wetlands, lakes, and uplands that was built alongside a compatible land cover dataset, sharing the same classifications. We show CH₄ fluxes can be split by broad land cover characteristics. The dataset is useful for comparison against new field data and model parameterization or validation.

This study is topical and provides a state-of-the-art scientific overview of data availability from bottom-up and top-down CO₂ fossil emissions and CO₂ land fluxes in the EU27+UK. The data integrate recent emission inventories with ecosystem data, land carbon models and regional/global inversions for the European domain, aiming at reconciling CO₂ estimates with official country-level UNFCCC national GHG inventories in support to policy and facilitating real-time verification procedures.

This study presents a dataset of volcanic sulfur dioxide (SO₂) emissions from 2005–2017. Measurements were obtained by Network for Observation of Volcanic and Atmospheric Change (NOVAC) scanning differential optical absorption spectrometer (ScanDOAS) instruments at 32 volcanoes and processed using a standardized procedure. We show statistics of volcanic gas emissions under a variety of conditions and compare them with averages derived from measurements from space and historical inventories.

Biogenic volatile organic compounds (VOCs) play a critical role in earth-system processes: they are main players in the formation of tropospheric O₃ and secondary aerosols, which have a significant impact on climate, human health and crops. A complex mixture of VOCs, formed as a result of physicochemical and biological processes, is released into the atmosphere from the forest floor. This review presents data on the composition of VOCs and contribution of various processes to their emissions.

Atmospheric blocking is associated with stationary, self-sustaining and long-lasting high-pressure systems. They can cause or at least influence surface weather extremes, such as heat waves, cold spells, heavy precipitation events, droughts or wind extremes. The location of the blocking determines where and what type of extreme event will occur. These relationships are also important for weather prediction and may change due to global warming.

This is a collective effort to describe the state of the art in Mediterranean cyclone dynamics, climatology, prediction (weather and climate scales) and impacts. More than that, the paper focuses on the future directions of research that would advance the broader field of Mediterranean cyclones as a whole. Thereby, we propose interdisciplinary cooperation and additional modelling and forecasting strategies, and we highlight the need for new impact-oriented approaches to climate prediction.

This review of air quality research focuses on developments over the past decade. The article considers current and future challenges that are important from air quality research and policy perspectives and highlights emerging prominent gaps of knowledge. The review also examines how air pollution management needs to adapt to new challenges and makes recommendations to guide the direction for future air quality research within the wider community and to provide support for policy.

In the atmosphere over the Indian Ocean, intense anthropogenic pollution from Southeast Asia mixes with pristine oceanic air. During the winter monsoon, high pollution levels are regularly observed over the entire northern Indian Ocean, while during the summer monsoon, clean air dominates. Here, we review current progress in detecting and understanding atmospheric gas-phase composition over the Indian Ocean and its impacts on the upper atmosphere, oceanic biogeochemistry, and marine ecosystems.

Landscape fire plume height controls fire emissions release in the atmosphere, in particular their transport that may also affect the longevity, chemical conversion, and fate of the plumes chemical constituents. Here, we review how such landscape-scale fire smoke plume injection heights are represented in large-scale atmospheric transport models aiming to represent the impacts of wildfire emissions on component of the Earth system.

Biomass burning is one of the largest sources of atmospheric pollutants worldwide. This paper presents an up-to-date compilation of emission factors for over 120 trace gas and aerosol species from the different forms of open vegetation fires and domestic biofuel use, based on an analysis of over 370 published studies. Using these emission factors and current global burning activity data, the annual emissions of important species released by the various types of biomass burning are estimated.

This is a synthesis of the atmospheric mercury (Hg) monitoring data available in recent years (2011–2015) in the Arctic and in Antarctica along with a comparison of these observations with numerical simulations using four cutting-edge global models. Based on this comparison, we discuss whether the processes that affect atmospheric Hg seasonality and interannual variability are appropriately represented in the models, and identify remaining research gaps.

Reliable quantification of air-surfaces flux of elemental mercury vapor (Hg⁰) is crucial for understanding Hg global biogeochemical cycles. In this study, we provide a comprehensive review on the state of science in the atmosphere-surface exchange of elemental Hg. We compiled an up-to-date global observational flux database and discuss the implication of flux data on global Hg budget. The knowledge gap and research needs for future measurements and modeling efforts were discussed.

For more than 20 years, scientists and engineers have tried to design simple sampling devices that can collect gaseous elemental mercury from the atmosphere without the use of a pump. A thorough review of the sampler designs that have been presented so far suggests that while some may be suitable for measuring higher air concentrations close to sources, none of them have the accuracy and precision required to record the low atmospheric mercury concentrations prevalent in background regions.

Hygroscopicity is one of the most important properties of aerosol particles, and a number of experimental techniques, which differ largely in principles, configurations and cost, have been developed to investigate hygroscopic properties of atmospherically relevant particles. Our paper provides a comprehensive and critical review of available techniques for aerosol hygroscopicity studies.

Feedbacks of acidity and atmospheric multiphase chemistry in deliquesced particles and clouds are crucial for the tropospheric composition, depositions, climate, and human health. This review synthesizes the current scientific knowledge on these feedbacks using both inorganic and organic aqueous-phase chemistry. Finally, this review outlines atmospheric implications and highlights the need for future investigations with respect to reducing emissions of key acid precursors in a changing world.

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.

Urban air pollution is a major global environmental health challenge. Establishing associations between exposure to urban aerosols and human health outcomes requires reliable aerosol measurements. Of particular importance are measurements of urban aerosol particle size distributions. This review critically analyzes global trends in urban aerosol particle size distributions in order to provide insights into air pollution in cities and guidance for the future for air quality monitoring networks.

We review the capability of satellite observations of atmospheric methane to quantify methane emissions on all scales. We cover retrieval methods, precision requirements, inverse methods for inferring emissions, source detection thresholds, and observations of system completeness. We show that current instruments already enable quantification of regional and national emissions including contributions from large point sources. Coverage and resolution will increase significantly in coming years.

Accurately projecting future climate change requires a good methane modeling. However, how good the current models are and what are the key improvements needed remain unclear. This paper reviews the 40 published methane models to characterize the strengths and weakness of current methane models and further lay out the roadmap for future model improvements.

This study made an detailed understanding on production, consumption and fluxes of methane from different sub-ecosystems of Sundarbans mangrove forest. The mangrove environment was found to be rich in organic carbon content as well as methane concentration. A most of the produced methane transported to the atmosphere where 85 % of total supply undergoes photo-oxidation. Like sediment estuaries are also methane supersatuarated and about 70 % of methane within estuary undergoes microbial oxidation.

Understanding and quantifying the global methane (CH₄) budget is important for assessing realistic pathways to mitigate climate change. We have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. This is the second version of the review dedicated to the decadal methane budget, integrating results of top-down and bottom-up estimates.

Excessive atmospheric reactive nitrogen (N_r) deposition can cause a series of negative effects. Thus, it is necessary to accurately estimate N_r deposition to evaluate its impact on the ecosystems and environment. Scientists attempted to estimate surface N_r concentration and deposition using satellite retrievals. We give a thorough review of recent advances in estimating surface N_r concentration and deposition using satellite retrievals of NO₂ and NH₃ and summarize the existing challenges.

Silver iodide is one of the best-investigated ice nuclei. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Nevertheless, many open questions remain. This paper gives an overview of silver iodide as an ice nucleus and tries to identify the factors that influence the ice nucleation ability of silver iodide.

Tropospheric {H₂O,δD} pairs can be observed by remote sensing techniques, but the data quality strongly depends on a comprehensive consideration of the complex nature and a careful calibration of the remote sensing data pairs. This paper reviews the quality assurance/documentation activities of the MUSICA project and demonstrates that MUSICA’s ground-based FTIR and space-based IASI {H₂O,δD} pair products are accurate and can be generated at a global scale with high resolution and for long periods.

Coral reefs are a strong source of atmospheric sulfur through stress-induced emissions of dimethylsulfide (DMS). This biogenic sulfur can influence aerosol and cloud properties and, consequently, the radiative balance over the ocean. DMS emissions may therefore help to mitigate coral physiological stress via increased low-level cloud cover and reduced sea surface temperature. The importance of DMS in coral physiology and climate is reviewed and the implications for coral bleaching are discussed.

Fires, including extreme fire seasons, and fire emissions are more common in the Arctic. A review and synthesis of current scientific literature find climate change and human activity in the north are fuelling an emerging Arctic fire regime, causing more black carbon and methane emissions within the Arctic. Uncertainties persist in characterizing future fire landscapes, and thus emissions, as well as policy-relevant challenges in understanding, monitoring, and managing Arctic fire regimes.

Great progress has been made in computer modelling and simulation of the whole climate system, including the stratosphere. Since the late 20th century we also gained a much clearer understanding of how the stratosphere interacts with the lower atmosphere. The latest generation of numerical prediction systems now explicitly represents the stratosphere and its interaction with surface climate, and here we review its role in long-range predictions and projections from weeks to decades ahead.

In recent years, it has emerged that there is an affinity between stratospheric variability and surface events. Waves from the troposphere interacting with the mean flow drive much of the variability in the polar vortex, sudden stratospheric warmings and tropical quasi-biennial oscillation. Here we review the historical evolution of established knowledge of the stratosphere's global structure and dynamical variability, along with recent advances and theories, and identify outstanding challenges.

Magnetospheric physics is in an extremely vibrant phase, with a number of ongoing and highly successful missions, e.g., Cluster, THEMIS, Van Allen Probes, and the MMS spacecraft, providing the most amazing observations and data sets. Since there are many fundamental and unsolved problems, in this paper I have addressed selected topics of ULF wave–charged particle interactions which encompass many special fields of radiation belt, ring current and plasmaspheric physics.

Because a systematic difference between measurements of water vapor performed by space-borne observing instruments in the microwave spectral domain and their numerical modeling was recently highlighted, this work discusses and gives an overview of the various errors and uncertainties associated with each element in the comparison process. Indeed, the knowledge of absolute errors in any observation of the climate system is key, more specifically because we need to detect small changes.

Remote sensing of atmospheric state variables typically relies on the inverse solution of the radiative transfer equation. An adequately characterized retrieval provides information on the uncertainties of the estimated state variables as well as on how any constraint or a priori assumption affects the estimate. This paper summarizes related techniques and provides recommendations for unified error reporting.

The properties and fate of individual airborne particles can be significantly different, leading to distinct environmental impacts (e.g., climate and human health). While many instruments only analyze an ensemble of these particles, single-particle Raman spectroscopy enables unambiguous characterization of individual particles. This paper comprehensively reviews the applications of such a technique in studying atmospheric particles, especially for their physicochemical processing.

This paper serves as an introduction to the special issue "Twenty-five years of operations of the Network for the Detection of Atmospheric Composition Change (NDACC)". It describes the origins of the network, its actual status, and some perspectives for its future evolution in the context of atmospheric sciences.

Vegetated coastal habitats (mangroves, seagrass meadows, salt marshes and macroalgal beds) are key contributors to the marine carbon budget, but remain hidden in the representation of the coastal carbon budget. While they have been acknowledged to play an important role in carbon burial, this is small compared to the export flow, which may lead to carbon sequestration beyond these habitats. The carbon fluxes supported by vegetated coastal habitats are globally relevant.

Plankton models have become an integral part in marine ecosystem and biogeochemical research. These models differ in complexity and in their number of parameters. How values are assigned to parameters is essential. An overview of major methodologies of parameter estimation is provided. Aspects of parameter identification in the literature are diverse. Individual findings could be better synthesized if notation and expertise of the different scientific communities would be reasonably merged.

Agropedogenesis, i.e. soil development under agricultural use, is the anthropogenic modification of soil and environmental factors for optimization of crop production. Maximization of only this function, crop production, leads to declines in all other soil functions and consequently promotes uniformity in soil properties around the globe. Here we developed a new scientific background for the theory of agropedogenesis and the identification of soil degradation stages.

Australian vegetation phenology is highly variable due to the diversity of ecosystems on the continent. We explore continental-scale variability using satellite remote sensing by broadly classifying areas as seasonal, non-seasonal, or irregularly seasonal. We also examine ecosystem-scale phenology using phenocams and show that some broadly non-seasonal ecosystems do display phenological variability. Overall, phenocams are useful for understanding ecosystem-scale Australian vegetation phenology.

The 4 per 1000 initiative aims to restore carbon storage in soils to both mitigate climate change and contribute to food security. The French National Institute for Agricultural Research conducted a study to determine the carbon storage potential in French soils and associated costs. This paper is a part of that study. It reviews recent advances concerning the mechanisms that controls C stabilization in soils. Synthetic figures integrating new concepts should be of pedagogical interest.

This paper describes the methods for combining models and data to understand how nutrients and pollutants move through natural systems. The methods are analogous to the process of weather forecasting in which previous information is combined with new observations and a model to improve our knowledge of the internal state of the physical system. The methods appear highly diverse but the paper shows that they are all examples of a single underlying formalism.

This paper provides the formalism and examples of how observation operators can be used, in combination with data assimilation or retrieval techniques, to better ingest satellite products in a manner consistent with the dynamics of the Earth system expressed by models.

The partitioning of evapotranspiration into evaporation from soil and transpiration from plants is crucial for a wide range of parties, from farmers to policymakers. In this work, we focus on a particular partitioning method, based on the stable isotopic analysis of water. In particular, we aim at highlighting the challenges that this method is currently facing and, in light of recent methodological developments, propose ways forward for the isotopic-partitioning community.

This review synthesized current knowledge of deep-sea food webs and provided a preliminary analysis of global geographic patterns in the biochemical composition of deep-water organisms. Our results revealed both latitudinal and depth wise trends in the biochemical composition of deep-sea animals. In addition, the link across latitudes between surface primary production and deep-water communities was highlighted, which has important implications in the face of global climate change.

Key findings are the nearly optimal response of T to atmospheric water vapor pressure deficits across methods and scales. Additionally, the notion that T / ET intermittently approaches 1, which is a basis for many partitioning methods, does not hold for certain methods and ecosystems. To better constrain estimates of E and T from combined ET measurements, we propose a combination of independent measurement techniques to better constrain E and T at the ecosystem scale.

It is known that CO₂ fixation by photoautotrophic organisms is the major sink from the atmosphere. While biologists are aware that CO₂ fixation also occurs in heterotrophic organisms, this route of inorganic carbon, and its quantitative role, is hardly recognized in biogeochemistry. We demonstrate that a considerable amount of CO₂ is fixed annually through anaplerotic reactions in heterotrophic organisms, and a significant quantity of inorganic carbon is temporally sequestered in biomass.

In recent years, multiple estimates of the global air–sea CO₂ flux emerged from upscaling shipboard pCO₂ measurements. They are however limited to the open-ocean domain and do not consider the coastal ocean, i.e. a significant marine sink for CO₂. We build towards an integrated pCO₂ product that combines both the open-ocean and coastal-ocean domain and focus on the evaluation of the common overlap area of these products and how well the aquatic continuum is represented in the new climatology.

This description and mapping of coastal sea level monitoring networks in the Mediterranean and Black seas reveals the existence of 240 presently operational tide gauges. Information is provided about the type of sensor, time sampling, data availability, and ancillary measurements. An assessment of the fit-for-purpose status of the network is also included, along with recommendations to mitigate existing bottlenecks and improve the network, in a context of sea level rise and increasing extremes.

Global mean sea-level change observed from 1993 to 2016 (mean rate of 3.05 mm yr⁻¹) matches the combined effect of changes in water density (thermal expansion) and ocean mass. Ocean-mass change has been assessed through the contributions from glaciers, ice sheets, and land water storage or directly from satellite data since 2003. Our budget assessments of linear trends and monthly anomalies utilise new datasets and uncertainty characterisations developed within ESA's Climate Change Initiative.

A new method of observing ocean heat content throughout the entire ocean depth is provided. The new method is compared with simulated ocean heat content changes from climate models. The comparisons are carried out in various depth layers of the ocean waters. It is found that there is excellent agreement between the models and the observations. Furthermore, we propose that changes to ocean heat content be used as a fundamental metric to evaluate climate models.

Over the past decade, understanding of the Indian Ocean has progressed through new observations and advances in theory and models of the oceanic and atmospheric circulation. This review brings together new understanding of the ocean–atmosphere system in the Indian Ocean, describing Indian Ocean circulation patterns, air–sea interactions, climate variability, and the critical role of the Indian Ocean as a clearing house for anthropogenic heat.

Geomorphometry, the science of quantitative terrain characterization, has traditionally focused on the investigation of terrestrial landscapes. More recently, a suite of geomorphometric techniques have been applied to characterize the seafloor. The dynamic, four-dimensional nature of the marine environment and differences in data collection methods cause issues for geomorphometry that are specific to marine applications. This article offers the first review of marine geomorphometry to date.

The region south of Cape Farewell (SCF) is recognized as a deep convection site. Convection deeper than 1300 m occurred SCF in 2015 and persisted during three additional winters. Extreme air–sea buoyancy fluxes caused the 2015 event. For the following winters, air–sea fluxes were close to the climatological average, but local cooling above 800 m and the advection below 1200 m of a fresh anomaly from the Labrador Sea decreased stratification and allowed for the persistence of deep convection.

Dissolved carbon dioxide levels in the oceans are rising and this is causing a drop in the pH (ocean acidification). This potentially effects all marine organisms, including those in polar regions. Sea ice algae are naturally exposed to a wide range of pH and CO₂ concentrations, particularly during the ice formation and melting cycles. However, all studies so far have shown ice algae to be quite resilient to change. This includes the effects of co-stressors such as light, iron and temperature.

The Indian Ocean receives a large proportion of plastics, but very few studies have addressed the sources, transport pathways, and sinks. There is a scarcity of observational data for the Indian Ocean. Most plastic sources are derived from rivers, although the amount derived from fishing activity (ghost nets, discarded ropes) is unknown. The unique topographic features of the Indian Ocean that create the monsoons and reversing currents have a large influence on the transport and sinks.

Cyanobacteria blooms can strongly aggravate eutrophication problems of water bodies. Their controls are, however, not comprehensively understood, which impedes effective management and protection plans. Here we review the current understanding of cyanobacteria blooms. Juxtaposition of respective field and laboratory studies with state-of-the-art mathematical models reveals substantial uncertainty associated with nutrient demands, grazing, and death of cyanobacteria.

Upwelling in the coastal ocean triggers biological productivity and thus enhances fisheries. Therefore, understanding the phenomenon of upwelling and the underlying mechanisms is important. In this paper, the present understanding of the upwelling along the coastline of the Indian Ocean from the coast of Africa all the way up to the coast of Australia is reviewed. The review provides a synthesis of the physical processes associated with upwelling and its impact on the marine ecosystem.

Here, we synthesize the results from 62 studies reporting in situ rates of seagrass metabolism to highlight spatial and temporal variability in oxygen fluxes and inform efforts to use seagrass to mitigate ocean acidification. Our analyses suggest seagrass meadows are generally autotrophic and variable in space and time, and the effects on seawater oxygen are relatively small in magnitude.

Silicon is the second most abundant element of the Earth's crust. In this review, we show that silicon inputs and outputs, to and from the world ocean, are 57 % and 37 % higher, respectively, than previous estimates. These changes are significant, modifying factors such as the geochemical residence time of silicon, which is now about 8000 years and 2 times faster than previously assumed. We also update the total biogenic silica pelagic production and provide an estimate for sponge production.

We carried out a literature review and an opinion poll of the JERICO-NEXT community to identify the main environmental threats in European coastal areas and gaps in monitoring. The need for improved monitoring was highlighted, e.g. through improved design and monitoring effort and better links with new technologies. The findings underpin the JERICO-NEXT science strategy to integrate linkages between physical, chemical, and biological parameters to address scientific and policy needs.

Freshwater in the Arctic Ocean plays a critical role in the global climate system by impacting ocean circulations, stratification, mixing, and emergent regimes. In this review paper we assess how Arctic Ocean freshwater changed in the 2010s relative to the 2000s. Estimates from observations and reanalyses show a qualitative stabilization in the 2010s due to a compensation between a freshening of the Beaufort Gyre and a reduction in freshwater in the Amerasian and Eurasian basins.

TEOS-10 is the present international standard for thermodynamic properties of water, ice, seawater and humid air recommended for geosciences by leading international organisations such as UNESCO/IOC and IUGG. TEOS-10 incorporates an extended manifold of different experimental data for those substances, collected from publications over many decades, in an unprecedentedly compact, consistent, comprehensive and accurate way.

This paper provides a comprehensive review and up-to-date synthesis of the observed changes in air temperature, precipitation, seasonal snow cover, mountain glaciers, permafrost, freshwater ice cover, and river discharge over the interior of western Canada since the mid- or late 20th century. Important long-term observational networks and data sets are described, and qualitative linkages among the changing Earth system components are highlighted.

In the field of Disaster Risk Reduction (DRR), there is a proliferation of research into different ways to measure, represent, and ultimately quantify differential social vulnerability to natural hazards. This study shows how the same census data but three alternative multivariate methodologies can lead to radical differences in our assessment of the most vulnerable population groups to flood risk. A case study of the 2013 floods in the Parrett catchment, Somerset (UK), provides context.

The gushing of water from flowing wells is a natural phenomenon of interest to the public. This review demonstrates that this spectacular phenomenon also instigated the science of groundwater and can be considered a root of groundwater hydrology. Observations of flowing wells not only led to the foundation of many principles of traditional groundwater hydrology but also played a vital role in the paradigm shift from aquitard-bound flow to cross-formational flow driven by topography.

Vertisols are cracking clayey, arable soils that often overlay groundwater reservoirs. The soil cracks enable flow that bypasses soil blocks, which results in both relatively fresh recharge of the underlying groundwater and contamination with reactive contaminants. These special phenomena, as well as unique mechanism of salinization after cultivation and relative resilience to contamination by nitrate typical to groundwater under vertisols, are reviewed in this study.

This paper compiles most of the studies (as far as the authors are aware) on the design of sensor networks for measurement of precipitation and streamflow. The literature shows that there is no overall consensus on the methods for the evaluation of sensor networks, as different design criteria often lead to different solutions. This paper proposes a methodology for the classification of methods, and a general framework for the design of sensor networks.

This study presents a systematic review of 128 papers that apply multi-criteria decision-making (MCDM) tools to flood problems, aiming to provide an overall picture of what has motivated researchers in 37 different countries over the past 2 decades. A wide range of applications were identified, highlighting the utility of MCDM as a decision support tool in all stages of the flood management process.

Weather and water extremes have devastating effects each year. One of the principal challenges for society is understanding how extremes are likely to evolve under the influence of changes in climate, land cover, and other human impacts. This paper provides a review of the methods and challenges associated with the detection, attribution, management, and projection of nonstationary weather and water extremes.

This research reviews flood risk within the Lagos area of Nigeria over the period 1968 to 2012. During this period, floods have caused harm to millions of people physically, emotionally, and economically. Arguably over this period the efforts of stakeholders to address the challenges appear to have been limited by, among other things, lack of reliable data, lack of awareness among the population affected, and lack of knowledge of flood risk mitigation. Recommendations are made for flood modeling.

This study presents a comprehensive review of models and emerging approaches for predicting urban surface water flooding driven by intense rainfall. It explores the advantages and limitations of existing models and identifies major challenges. Issues of model complexities, scale effects, and computational efficiency are also analysed. The results will inform scientists, engineers, and decision-makers of the latest developments and guide the model selection based on desired objectives.

We apply the green- and blue-water perspective to Amazonia's water resources to highlight trade-offs that may arise with future land use change. We question how future irrigation may supply additional water vapour to the atmosphere with growing agricultural production. Maintaining precipitation recycling could prevent degradation of rainfall-dependent terrestrial ecosystems and has the potential to minimize blue-water trade-offs between up- and downstream water users within the Amazon Basin.

Ideas to mitigate climate change include the large-scale cultivation of fast-growing plants to capture atmospheric CO₂ in biomass. To maximize the productivity of these plants, they will likely be irrigated. However, there is strong disagreement in the literature on how much irrigation water is needed globally, potentially inducing water stress. We provide a comprehensive overview of global irrigation demand studies for biomass production and discuss the diverse underlying study assumptions.

We present a review of how transport and fate of micropollutants, i.e., pharmaceuticals and pesticides that are found in groundwater worldwide, can be studied using a laboratory setup of column experiments. Hereby, transport relevant processes are presented and which compounds and which of their properties can be studied with column experiments. We discuss advantages of this laboratory method and show weaknesses and problems.

The country of Myanmar and its abundant water resources are facing major challenges due to political and economic reforms, massive investments from neighbouring countries and climate change impacts. Publications on current and future impacts from human activities and climate change on Myanmar's river basins have been reviewed in order to gain an overview of the key drivers in these human–water dynamics. The review reveals the relevance of this information with regard to human–water interactions.

This paper reviews literature surrounding many aspects of socio-hydrological modelling; this includes a background to the subject of socio-hydrology, reasons why socio-hydrological modelling would be used, what is to be modelled in socio-hydrology and concepts that underpin this, as well as several modelling techniques and how they may be applied in socio-hydrology.

The complementary principle is an important methodology for estimating actual evaporation by using routinely observed meteorological variables. This review summaries its 56-year development, focusing on how related studies have shifted from adopting a symmetric linear complementary relationship to employing generalized nonlinear functions. We also compare the polynomial and sigmoid types of generalized complementary functions and discuss their future development.

Land–atmosphere interactions are key for the exchange of water, energy, and carbon dioxide, especially in the tropics. We here review some of the recent findings on land–atmosphere interactions in the tropics and where we see potential challenges and paths forward.

Water isotopes are a scientific tool that can be used to identify sources of water and answer questions such as From which soil depths do plants take up water?, which are highly relevant under changing climatic conditions. In the past, the measurement of water isotopes required tremendous effort. In the last decade methods have advanced and can now be applied in the field. Herein, we review the current status of direct field measurements of water isotopes and discuss future applications.

We analyse water storage compartments, water flows, and human water use sectors included in 16 global water models that provide simulations for the Inter-Sectoral Impact Model Intercomparison Project phase 2b. We develop a standard writing style for the model equations. We conclude that even though hydrologic processes are often based on similar equations, in the end these equations have been adjusted, or the models have used different values for specific parameters or specific variables.

This review paper investigates the determinants of modelling choices for numerous applications of 1-D free-surface flow and morphodynamics in hydrology and hydraulics. Each case study has a signature composed of given contexts (spatiotemporal scales, flow typology, and phenomenology) and chosen concepts (refinement and subscales of the flow model). This review proposes a normative procedure possibly enriched by the community for a larger, comprehensive and updated image of modelling strategies.

This paper explores the benefits and advantages of R's usage in hydrology. We provide an overview of a typical hydrological workflow based on reproducible principles and packages for retrieval of hydro-meteorological data, spatial analysis, hydrological modelling, statistics, and the design of static and dynamic visualizations and documents. We discuss some of the challenges that arise when using R in hydrology as well as a roadmap for R’s future within the discipline.

The notion of a measure to quantify the degree of heterogeneity of a region from which information is required to estimate the magnitude of events at ungauged sites is introduced. These heterogeneity measures are needed to compare regions, evaluate the impact of particular sites, and rank the performance of delineating methods. A framework to define and assess their desirable properties is proposed. Several heterogeneity measures are presented and/or developed to be assessed, giving guidelines.

This article presents the most important facts on the life and scientific achievements of Steponas Kolupaila (1892–1964) – one of the most famous hydrologists of the 20th century. This Lithuanian scientist is especially well known for his book Bibliography of Hydrometry.

This paper present the results of interviews that were conducted with the developers of apps dedicated to avalanche risk communication. The study investigates the context of their development to determine how choices of content and visualization were made as well as how their effectiveness is evaluated. Results show that consensus is achieved in terms of message but not in terms of visualization. However, progress remains in terms of effectiveness evaluation.

This paper makes a rather exhaustive overview of current knowledge of past, current, and future aspects of cryospheric issues in continental Europe and makes a number of reflections of areas of uncertainty requiring more attention in both scientific and policy terms. The review paper is completed by a bibliography containing 350 recent references that will certainly be of value to scholars engaged in the fields of glacier, snow, and permafrost research.

We review what can be inferred about permafrost in the mountains of the Hindu Kush Himalaya region. This is important because the area of permafrost exceeds that of glaciers in this region. Climate change will produce diverse permafrost-related impacts on vegetation, water quality, geohazards, and livelihoods. To mitigate this, a better understanding of high-elevation permafrost in subtropical latitudes as well as the pathways connecting environmental change and human livelihoods, is needed.

Laboratory experiments that assess microplastic (MP) impact on the terrestrial environment require information on common soil MP concentrations. We reviewed item numbers and mass concentrations recorded in 23 studies, with 223 sampling sites in total with respect to the underlying entry pathways, land uses and vicinities. Common values included amounts of up to 13 000 items kg⁻¹ and 4.5 mg kg⁻¹ dry soil. Based on the collected data, we identified problems in past field studies.

Research data are becoming increasingly available online with tantalizing possibilities for reanalysis. However harmonizing data from different sources remains challenging. Using the soils community as an example, we walked through the various strategies that researchers currently use to integrate datasets for reanalysis. We find that manual data transcription is still extremely common and that there is a critical need for community-supported informatics tools like vocabularies and ontologies.

Via anthropogenic input, microplastics (MPs) today represent a part of the soil organic matter. We analyzed studies on passive translocation, active ingestion, bioaccumulation and adverse effects of MPs on multicellular soil faunal life. These studies on a wide range of soil organisms found a recurring pattern of adverse effects on motility, growth, metabolism, reproduction, mortality and gut microbiome. However, the shape and type of the experimental MP often did not match natural conditions.

In this study, TEC and positional variations have been examined seperately regarding the earthquake, which occurred in the Aegean Sea. Then The correlation of the said ionospheric variation with the positional variation has been investigated; it can be said definitely that it is a seismic origin anomaly; it is believed that upper air, geophysical, and geological data are required.

About 200 years ago in 1815 Sir James Hall made his famous analogue experiments, which showed probably for the first time that natural folds in ductile rock are the result of a horizontal compression. If such rocks are extended, then the rock layers can thin only locally, which is a process termed necking, and the resulting structure is often termed pinch-and-swell. We review here theoretical and experimental results on folding and necking on all geological scales.

The paper reviews age constraints for a short-lived episode of deformation in Svalbard (Ellesmerian and Svalbardian orogenies) that is thought to have occurred ca. 380–360 million years ago. The review mostly discusses (but is not limited to) paleontological, palynological, and geochronological evidence. The review finds it most unlikely that the event discussed ever occurred in Svalbard.

The seismo-electromagnetic method is used for non-invasive subsurface exploration, showing interesting results for detecting fluids such as water, oil, gas, CO₂, or ice, and to better characterize the subsurface in terms of porosity, permeability, and fractures. We describe theoretical background, the role of key parameters, recent theoretical and numerical developments, and field and laboratory observations to show that this method can bring advantages compared to classical geophysical method.

Geodynamic modelling provides a powerful tool to investigate processes in the Earth’s crust, mantle, and core that are not directly observable. In this review, we present a comprehensive yet concise overview of the modelling process with an emphasis on best practices. We also highlight synergies with related fields, such as seismology and geology. Hence, this review is the perfect starting point for anyone wishing to (re)gain a solid understanding of geodynamic modelling as a whole.

This paper introduces a new method for mapping electric fields in the magnetosphere along geomagnetic field lines. This is important for conjugate studies of electric fields measured in the ionosphere by SuperDARN radars, and at spacecraft carrying electric field probes. First elementary methods in a dipole field are reviewed and then the theory of of a new method described for general magnetic field models. The method is tested in a dipole model with a Harris magnetotail field.

The method of electric field mapping along geomagnetic field lines, derived in an accompanying paper, is applied to the International Geomagnetic Reference Field. Formulae for the geomagnetic field gradient tensor are derived and these are used in a software package developed to map the electric field. A number of examples are presented illustrating the method. The method will be of importance in conjugate studies of ionospheric convection when the external magnetic field can be neglected.

This is a review paper that summarises the current understanding of the lower thermosphere–ionosphere (LTI) in terms of measurements and modelling. The LTI is the transition region between space and the atmosphere and as such of tremendous importance to both the domains of space and atmosphere. The paper also serves as the background for European Space Agency Earth Explorer 10 candidate mission Daedalus.

This paper examines how ionospheric physics emerged as a research speciality in Britain, Germany, and the United States in the first 4 decades of the 20th century. It argues that the formation of this discipline can be viewed as the confluence of four deep-rooted traditions in which scientists and engineers transformed, from within, research areas connected to radio wave propagation and geomagnetism.

A significant number of studies published over the last 15 years demonstrate that there is strong two-way coupling between the magnetosphere and ionosphere during geomagnetic activity; not only does the ionosphere respond to magnetospheric forcing during storms, but through its impact on wave generation, wave-particle interactions, ion outflow and mass loading at the dayside magnetopause and in the magnetotail, dense plasma plumes modulate the subsequent magnetospheric dynamics.

The behaviour of mirror mode waves in Venus's magnetosheath is investigated for solar minimum and maximum conditions. It is shown that the total observational rate of these waves does not change much; however, the distribution over the magnetosheath is significantly different, as well as the growth and decay of the waves during these different solar activity conditions.

In this paper, we present a compilation of the different radiation transport codes for the Martian surface that are currently used by various space agencies and institutions. In addition, as the execution of the tasks necessary to process all of these radiation data requires a high computational processing capacity, we link it to cloud computing, which is found to be an appropriate tool regarding the required resources.

The Radiation Assessment Detector (RAD), on board the Mars Science Laboratory (MSL) rover Curiosity, measures the energetic charged and neutral particles and the radiation dose rate on the surface of Mars. In this work we compare predicted electron/positron spectra with the signal measured by RAD. We find that the RAD electron/positron measurements agree well with the spectra predicted by Planetocosmics.

The solar wind magnetic field drapes around the active nucleus of comet 67P/CG, creating a magnetosphere. The solar wind density increases and with that the pressure, which compresses the magnetosphere, increasing the magnetic field strength near Rosetta. The higher solar wind density also creates more ionization through collisions with the gas from the comet. The new ions are picked-up by the magnetic field and generate mirror-mode waves, creating low-field high-density "bottles" near 67P/CG.

We have analysed the magnetic field measurements performed on the ROSETTA orbiter and the lander PHILAE during PHILAE's descent to comet 67P/Churyumov-Gerasimenko on 12 November 2014. We observed a new type of low-frequency wave with amplitudes of ~ 3 nT, frequencies of 20–50 mHz, wavelengths of ~ 300 km, and propagation velocities of ~ 6 km s⁻¹. The waves are generated in a ~ 100 km region around the comet a show a highly correlated behaviour, which could only be determined by two-point observations.

Galactic cosmic rays are high-energy particles from outside of the solar system. The products of their interaction with the atmosphere are counted by a network of neutron monitors. The number of cosmic rays reaching Earth is affected by the magnetic field embedded in the solar wind. The result is a number of regular variations in the neutron monitor data, including a diurnal variation. We have found that this variation is influenced by 1–2 h by the polarity of the Sun's magnetic field.

In situ spacecraft data in space plasma are obtained often as time series data. Using Taylor's frozen-in flow hypothesis, one can interpret the time series data as spatial variations swept by the slow and passing by the spacecraft. A quantitative method for estimating the error for Taylor's hypothesis is developed here.

For the processing of geomatics data, artificial intelligence (AI) offers overwhelming opportunities. The integration of AI approaches in geomatics has developed into the concept of geospatial artificial intelligence (GeoAI), which is a new paradigm for geographic knowledge discovery and beyond. This contribution outlines AI-based techniques for analysing and interpreting complex geomatics data. How AI approaches have been exploited for the interpretation of geomatic data is explained.

Remote sensing has played an important role in the study of land surface processes. Geostationary satellites, such as the GOES-R series, can observe the Earth every 5–15 min, providing us with more observations than widely used polar-orbiting satellites. Here, we outline current efforts utilizing geostationary observations in environmental science and look towards the future of GOES observations in the carbon cycle, ecosystem disturbance, and other areas of application in environmental science.

The task of evaluating competing models is fundamental to science. Models are evaluated based on an objective function, the choice of which ultimately influences what scientists learn from their observations. The mean absolute error (MAE) and root-mean-squared error (RMSE) are two such functions. Both are widely used, yet there remains enduring confusion over their use. This article reviews the theoretical justification behind their usage, as well as alternatives for when they are not suitable.

Mitigation planning and economic loss assessment generally rely on flood damage prediction models. However, unavailability of empirical data has limited the use of such models in data-scarce areas. This paper combines the vulnerability indicator and damage grade approach to develop a conceptual framework for predicting building damage in data-scarce regions. The framework can be implemented using only expert knowledge and facilitates transferability of flood damage models in data-scarce areas.

Communities need to be prepared to deal with increasing exposure to natural hazards. We compared and categorized hazard responses reported in over 300 community case studies. A global overview of local response actions can help local communities, policymakers and funding agencies to develop effective strategies to prepare for and manage natural disasters. We found that actions are typically hazard specific and most directed at individual and material well-being.

This paper discusses how uncertainties resulting from lack of knowledge are considered in a number of different natural hazard areas including floods, landslides and debris flows, dam safety, droughts, earthquakes, tsunamis, volcanic ash clouds and pyroclastic flows, and wind storms. As every analysis is necessarily conditional on the assumptions made about the nature of sources of such uncertainties it is also important to follow the guidelines for good practice suggested in Part 2.

This paper draws on the experiences of seven early career scientists, in different sectors and contexts, to explore the improved integration of natural hazard science into broader efforts to reduce the likelihood and impacts of disasters. We include recommendations for natural hazard scientists, to improve education, training, and research design and to strengthen institutional, financial, and policy actions. We hope to provoke discussion and catalyse changes that will help reduce disaster risk.

This invited perspective paper addresses how machine learning may change flood risk and impact assessments. It goes through different modelling components and provides an analysis of how current assessments are done without machine learning, current applications of machine learning and potential future improvements. It is based on a 2-week-long intensive collaboration among experts from around the world during the Understanding Risk Field lab on urban flooding in June 2019.

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