Earth System Processes Research Articles

Transient climate changes in a perturbed parameter ensemble of emissions-driven earth system model simulations

We describe results from a 57-member ensemble of transient climate change simulations, featuring simultaneous perturbations to 54 parameters in the atmosphere, ocean, sulphur cycle and terrestrial ecosystem components of an earth system model (ESM). These emissions-driven simulations are compared against the CMIP3 multi-model ensemble of physical climate system models, used extensively to inform previous assessments of regional climate change, and also against emissions-driven simulations from ESMs contributed to the CMIP5 archive. Members of our earth system perturbed parameter ensemble (ESPPE) are competitive with CMIP3 and CMIP5 models in their simulations of historical climate. In particular, they perform reasonably well in comparison with HadGEM2-ES, a more sophisticated and expensive earth system model contributed to CMIP5. The ESPPE therefore provides a computationally cost-effective tool to explore interactions between earth system processes. In response to a non-intervention emissions scenario, the ESPPE simulates distributions of future regional temperature change characterised by wide ranges, and warm shifts, compared to those of CMIP3 models. These differences partly reflect the uncertain influence of global carbon cycle feedbacks in the ESPPE. In addition, the regional effects of interactions between different earth system feedbacks, particularly involving physical and ecosystem processes, shift and widen the ESPPE spread in normalised patterns of surface temperature and precipitation change in many regions. Significant differences from CMIP3 also arise from the use of parametric perturbations (rather than a multimodel ensemble) to represent model uncertainties, and this is also the case when ESPPE results are compared against parallel emissions-driven simulations from CMIP5 ESMs. When driven by an aggressive mitigation scenario, the ESPPE and HadGEM2-ES reveal significant but uncertain impacts in limiting temperature increases during the second half of the twenty-first century. Emissions-driven simulations create scope for development of errors in properties that were previously prescribed in coupled ocean–atmosphere models, such as historical CO2 concentrations and vegetation distributions. In this context, historical intra-ensemble variations in the airborne fraction of CO2 emissions, and in summer soil moisture in northern hemisphere continental regions, are shown to be potentially useful constraints, subject to uncertainties in the relevant observations. Our results suggest that future climate-related risks can be assessed more comprehensively by updating projection methodologies to support formal combination of emissions-driven perturbed parameter and multi-model earth system model simulations with suitable observational constraints. This would provide scenarios underpinned by a more complete representation of the chain of uncertainties from anthropogenic emissions to future climate outcomes.

A review of prokaryotic populations and processes in sub-seafloor sediments, including biosphere:geosphere interactions

A general review of the sub-seafloor biosphere is presented. This includes an update and assessment of prokaryotic cell distributions within marine sediments, current deepest 1922 m, and the impact of this on global sub-seafloor biomass estimates. These global estimates appear relatively robust to different calculation approaches and our updated estimate is 5.39 x 1029 cells, taking into consideration new data from very low organic matter South Pacific Gyre sediments. This is higher than other recent estimates, which is justified as several sediments, such as gas hydrate deposits and oil reservoirs, can have elevated cell concentrations. The proposed relationship between elevated cell concentrations and Milankovitch Cycles in sequential diatom rich layers at some sites, demonstrates not only a dynamic deep biosphere, but that the deep biosphere is an integral part of Earth System Processes over geological time scales. Cell depth distributions vary in different oceanographic provinces and this is also reflected in contrasting biodiversity. Despite this there are some clear common, sub-seafloor prokaryotes, for Bacteria these are the phyla Chloroflexi, Gammaproteobacteria, Planctomycetes and the candidate phylum JS1, and for Archaea uncultivated lineages within the phylum Crenarchaeota (Miscellaneous Crenarchaeotal Group and Marine Benthic Group B), Euryarchaeota (SAGMEG, Marine Benthic Group-D/Thermoplasmatales associated groups) and Thaumarchaeota (Marine Group I). In addition, spores, viruses and fungi have been detected, but their importance is not yet clear. Consistent with the direct demonstration of active prokaryotic cells, prokaryotes have been enriched and isolated from deep sediments and these reflect a subset of the total diversity, including spore formers that are rarely detected in DNA analyses. Activities are generally low in deep marine sediments (~ 10,000 times lower than in near-surface sediments), however, depth integrated activity calculations demonstrate that sub-surface sediments can be responsible for the majority of sediment activity (up to 90%), and hence, are biogeochemically important. Unlike near-surface sediments, competitive metabolisms can occur together and metabolism per cell can be 1,000 times lower than in culture, and below the lowest known maintenance energies. Consistent with this, cell turnover times approach geological time-scales (100 – 1,000’s of years). Prokaryotic necromass may be an important energy and carbon source, but this is largely produced in near-surface sediments as cell numbers rapidly decrease. However, this and deposited organic matter may be activated at depth as temperatures increase. At thermogenic temperatures methane and other hydrocarbons, plus H2, acetate and CO2 may be produced and diffuse upwards to feed the base of the biosphere (e.g. Nankai Trough and Newfoundland Margin). Temperature activation of minerals may also result in oxidation of sulphides and the formation of electron acceptors, plus H2 from low temperature (~ 55 °C) serpentenisation and water radiolysis. New mineral surface formation from fracturing, weathering and subduction etc. can also mechanochemically split water producing both substrates (H2) and oxidants (O2, H2O2) for prokaryotes. These and other biosphere:geosphere interactions may be important for sustaining a globally significant sub-seafloor biosphere.

Inter-Comparison and Validation of the FY-3A/MERSI LAI Product Over Mainland China

Leaf area index (LAI) is a key surface parameter that describes the structure of vegetation and plays an important role in Earth system process modeling. In this paper, a new set of LAI products (MERSI GLOBCARBON LAI) has been developed based on the GLOBCARBON LAI algorithm and one year of FY-3A/MERSI land surface reflectance data. MERSI GLOBCARBON LAI has been inter-compared and validated over mainland China against MODIS land surface reflectance (LSR) derived LAI (using the same algorithm) and field LAI measurements. MERSI GLOBCARBON LAI and MODIS GLOBCARBON LAI show continuous and smooth LAI distributions at the start and end of the growing season. For most areas in China, the two LAI products agree well. The temporal variation in MERSI GLOBCARBON LAI and MODIS GLOBCARBON LAI consistently follows the growing season. The largest LAI difference occurs during July, when MERSI shows a much higher frequency of retrievals than does MODIS. Through validation of LAI retrievals with field measurements, our study demonstrates that LAI derived from MERSI and MODIS land surface reflectance products have comparable accuracy. MODIS top-of-atmosphere simple ratio (MODIS TOA SR) is related to MERSI TOA SR with linear correlation coefficients greater than 0.6. After atmospheric correction, the correlation coefficient increases from 0.69 to 0.75 over cropland and from 0.82 to 0.93 over grassland. However, atmospheric correction can still give rise to substantial differences in the reflectance data between the two sensors. Furthermore, different land cover types and different terrain relief have contrasting influences on the atmospheric correction, and these influences reduce the agreement between the two LAI products. This study shows the great potential of FY-3A/MERSI data for global LAI retrieval.

Trend Analysis of Climate Variability over the West Bank - East London Area, South Africa (1975-2011)

In recent years, climate change has received considerable attention by the scientific community at different scales concerning its potential impacts on Earth system processes. This study focused at local scale by analysing trends in rainfall and temperature data for the West Bank–East London area in South Africa, spanning 36 years from 1975–2011. Sen’s and Man-Kendall non-parametric tests were performed on derived mean observed rainfall and temperature data to establish trends for monthly, seasonal, annual, and 30 year (1975–2005 and 1980–2011) climatic regimes. Results revealed that, 1977 recorded the highest annual rainfall (2272.9 mm) while the month of August received the highest total rainfall (493.8 mm) in 2002, whereas it never had rain in 1995. Seasonal and annual rainfall showed statistically no significant trend (at a = 0.10) while the magnitude of change varied between 1.87 mm (January) and -1.67 mm (September) across the study period. Rainfall decreased by 13.99 mm within the two climatic regimes. On the other hand, maximum and minimum annual mean temperature experienced an increasingly statistically significant trend (at a < 0.05) at 95% confidence level. February recorded the highest mean monthly temperature (21.8 °C) while July with the lowest (12.6 °C). Seasonal mean maximum temperature trends were statistically not significant (a = 0.10) while autumn minimum temperatures revealed a statistically significant trend (at a < 0.1). However, the period 1990-1999 predominantly experienced numerous extreme events. The seasonal trends showed substantial variability across the months and years during the study period. The significance of these findings lies in the linkage of rainfall and temperature to climate change and its potential impacts on vegetation in particular and changes in the ecology in general.

Evaluating the agreement between measurements and models of net ecosystem exchange at different times and timescales using wavelet coherence: an example using data from the North American Carbon Program Site-Level Interim Synthesis

Abstract. Earth system processes exhibit complex patterns across time, as do the models that seek to replicate these processes. Model output may or may not be significantly related to observations at different times and on different frequencies. Conventional model diagnostics provide an aggregate view of model–data agreement, but usually do not identify the time and frequency patterns of model–data disagreement, leaving unclear the steps required to improve model response to environmental drivers that vary on characteristic frequencies. Wavelet coherence can quantify the times and timescales at which two time series, for example time series of models and measurements, are significantly different. We applied wavelet coherence to interpret the predictions of 20 ecosystem models from the North American Carbon Program (NACP) Site-Level Interim Synthesis when confronted with eddy-covariance-measured net ecosystem exchange (NEE) from 10 ecosystems with multiple years of available data. Models were grouped into classes with similar approaches for incorporating phenology, the calculation of NEE, the inclusion of foliar nitrogen (N), and the use of model–data fusion. Models with prescribed, rather than prognostic, phenology often fit NEE observations better on annual to interannual timescales in grassland, wetland and agricultural ecosystems. Models that calculated NEE as net primary productivity (NPP) minus heterotrophic respiration (HR) rather than gross ecosystem productivity (GPP) minus ecosystem respiration (ER) fit better on annual timescales in grassland and wetland ecosystems, but models that calculated NEE as GPP minus ER were superior on monthly to seasonal timescales in two coniferous forests. Models that incorporated foliar nitrogen (N) data were successful at capturing NEE variability on interannual (multiple year) timescales at Howland Forest, Maine. The model that employed a model–data fusion approach often, but not always, resulted in improved fit to data, suggesting that improving model parameterization is important but not the only step for improving model performance. Combined with previous findings, our results suggest that the mechanisms driving daily and annual NEE variability tend to be correctly simulated, but the magnitude of these fluxes is often erroneous, suggesting that model parameterization must be improved. Few NACP models correctly predicted fluxes on seasonal and interannual timescales where spectral energy in NEE observations tends to be low, but where phenological events, multi-year oscillations in climatological drivers, and ecosystem succession are known to be important for determining ecosystem function. Mechanistic improvements to models must be made to replicate observed NEE variability on seasonal and interannual timescales.

Palynological perspectives on vegetation survey: a critical step for model-based reconstruction of Quaternary land cover

1. Quantitative reconstruction of past vegetation distribution and abundance from sedimentary pollen records provides an important baseline for understanding long term ecosystem dynamics and for the calibration of earth system process models such as regional-scale climate models, widely used to predict future environmental change. Most current approaches assume that the amount of pollen produced by each vegetation type, usually expressed as a relative pollen productivity term, is constant in space and time.2. Estimates of relative pollen productivity can be extracted from extended R-value analysis (Parsons and Prentice, 1981) using comparisons between pollen assemblages deposited into sedimentary contexts, such as moss polsters, and measurements of the present day vegetation cover around the sampled location. Vegetation survey method has been shown to have a profound effect on estimates of model parameters (Bunting and Hjelle, 2010), therefore a standard method is an essential pre-requisite for testing some of the key assumptions of pollen-based reconstruction of past vegetation; such as the assumption that relative pollen productivity is effectively constant in space and time within a region or biome.3. This paper systematically reviews the assumptions and methodology underlying current models of pollen dispersal and deposition, and thereby identifies the key characteristics of an effective vegetation survey method for estimating relative pollen productivity in a range of landscape contexts.4. It then presents the methodology used in a current research project, developed during a practitioner workshop. The method selected is pragmatic, designed to be replicable by different research groups, usable in a wide range of habitats, and requiring minimum effort to collect adequate data for model calibration rather than representing some ideal or required approach. Using this common methodology will allow project members to collect multiple measurements of relative pollen productivity for major plant taxa from several northern European locations in order to test the assumption of uniformity of these values within the climatic range of the main taxa recorded in pollen records from the region.

Addressing ‘deep’ uncertainty over long-term climate in major infrastructure projects: four innovations of the Thames Estuary 2100 Project

Climate change brings new challenges for traditional environmental risk management, particularly for major infrastructure projects, where the decisions made today can have long-term implications. A major challenge is that projections of future climate are deeply uncertain. If this uncertainty is not managed appropriately, long-lived infrastructure may need to be replaced or expensively retrofitted before the end of the design lifetime. The Thames Estuary 2100 Project (TE2100) was one of the first major infrastructure projects to explicitly recognise and address the issue of the deep uncertainty in climate projections throughout the planning process. In this paper, we discuss the innovations and techniques that were adopted in this case that enabled it to cope with this uncertainty. We classify the overall approach as ‘dynamic robustness’, which aims to build flexible strategies that can be changed over time as more is learnt or as conditions change. The project combined four key innovations: (1) the ‘decision-centric’ process; (2) the combination of numerical models and expert judgement to develop narrative sea level rise scenarios; (3) the adoption of an ‘Adaptation Pathways’ approach to identify the timing and sequencing of possible ‘pathways’ of adaptation measures over time under different scenarios; and (4) the development of a monitoring framework that triggers defined decision points. A secondary focus of this paper is an exploration of how climate information was used in TE2100. We suggest that the techniques employed in TE2100 imply different needs from climate science that may cause them to redefine their research priorities related to adaptation; namely a shift in emphasis away from probabilistic modelling, toward greater investment in observations and monitoring; improved understanding of historical climate variability; and improved understanding of physical Earth system processes and their representation in models to enhance ‘best guess’ models and to better bound future projections using narrative scenarios.

Big data visual analytics for exploratory earth system simulation analysis

Rapid increases in high performance computing are feeding the development of larger and more complex data sets in climate research, which sets the stage for so-called “big data” analysis challenges. However, conventional climate analysis techniques are inadequate in dealing with the complexities of today's data. In this paper, we describe and demonstrate a visual analytics system, called the Exploratory Data analysis ENvironment (EDEN), with specific application to the analysis of complex earth system simulation data sets. EDEN represents the type of interactive visual analysis tools that are necessary to transform data into insight, thereby improving critical comprehension of earth system processes. In addition to providing an overview of EDEN, we describe real-world studies using both point ensembles and global Community Land Model Version 4 (CLM4) simulations.

Brief Communication: Likelihood of societal preparedness for global change: trend detection

Abstract. Anthropogenic influences on earth system processes are now pervasive, resulting in trends in river discharge, pollution levels, ocean levels, precipitation, temperature, wind, landslides, bird and plant populations and a myriad of other important natural hazards relating to earth system state variables. Thousands of trend detection studies have been published which report the statistical significance of observed trends. Unfortunately, such studies only concentrate on the null hypothesis of "no trend". Little or no attention is given to the power of such statistical trend tests, which would quantify the likelihood that we might ignore a trend if it really existed. The probability of missing the trend, if it exists, known as the type II error, informs us about the likelihood of whether or not society is prepared to accommodate and respond to such trends. We describe how the power or probability of detecting a trend if it exists, depends critically on our ability to develop improved multivariate deterministic and statistical methods for predicting future trends in earth system processes. Several other research and policy implications for improving our understanding of trend detection and our societal response to those trends are discussed.

Multiscale coupling and multiphysics approaches in earth sciences: Theory

Measuring Earth material behaviour on time scales of millions of years transcends our current capability in the laboratory. We review an alternative path considering multiscale and multiphysics approaches with quantitative structure-property relationships. This approach allows a sound basis to incorporate physical principles such as chemistry, thermodynamics, diffusion and geometry-energy relations into simulations and data assimilation on the vast range of length and time scales encountered in the Earth. We identify key length scales for Earth systems processes and find a substantial scale separation between chemical, hydrous and thermal diffusion. We propose that this allows a simplified two-scale analysis where the outputs from the micro-scale model can be used as inputs for meso-scale simulations, which then in turn becomes the micro-model for the next scale up. We present two fundamental theoretical approaches to link the scales through asymptotic homogenisation from a macroscopic thermodynamic view and percolation renormalisation from a microscopic, statistical mechanics view.

Surface Transformations and Water Uptake on Liquid and Solid Butanol near the Melting Temperature

Water interactions with organic surfaces are of central importance in biological systems and many Earth system processes. Here we describe experimental studies of water collisions and uptake kinetics on liquid and solid butanol from 160 to 200 K. Hyperthermal D2O molecules (0.32 eV) undergo efficient trapping on both solid and liquid butanol, and only a minor fraction scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules either desorb within a few ms, or are taken up by the butanol phase during longer times. The water uptake and surface residence time increase with temperature above 180 K indicating melting of the butanol surface 4.5 K below the bulk melting temperature. Water uptake changes gradually across the melting point and trapped molecules are rapidly lost by diffusion into the liquid above 190 K. This indicates that liquid butanol maintains a surface phase with limited water permeability up to 5.5 K above the melting point. These surface observations are indicative of an incremental change from solid to liquid butanol over a range of 10 K straddling the bulk melting temperature, in contrast to the behavior of bulk butanol and previously studied materials.

Double Catastrophe: Intermittent Stratospheric Geoengineering Induced By Societal Collapse

Perceived failure to reduce greenhouse gas emissions has prompted interest in avoiding the harms of climate change via geoengineering, that is, the intentional manipulation of Earth system processes. Perhaps the most promising geoengineering technique is stratospheric aerosol injection (SAI), which reflects incoming solar radiation, thereby lowering surface temperatures. This paper analyzes a scenario in which SAI brings great harm on its own. The scenario is based on the issue of SAI intermittency, in which aerosol injection is halted, sending temperatures rapidly back toward where they would have been without SAI. The rapid temperature increase could be quite damaging, which in turn creates a strong incentive to avoid intermittency. In the scenario, a catastrophic societal collapse eliminates society’s ability to continue SAI, despite the incentive. The collapse could be caused by a pandemic, nuclear war, or other global catastrophe. The ensuing intermittency hits a population that is already vulnerable from the initial collapse, making for a double catastrophe. While the outcomes of the double catastrophe are difficult to predict, plausible worst-case scenarios include human extinction. The decision to implement SAI is found to depend on whether global catastrophe is more likely from double catastrophe or from climate change alone. The SAI double catastrophe scenario also strengthens arguments for greenhouse gas emissions reductions and against SAI, as well as for building communities that could be self-sufficient during global catastrophes. Finally, the paper demonstrates the value of integrative, systems-based global catastrophic risk analysis.

A ‘Sedimentary Record’ of Opportunities

Several recent National Academy of Sciences publications (NRC 2005, 2010a, 2010b, 2011, 2012) and a subsequent community driven initiative report (Transitions 2012) provide the earth surface scientific community a framework of high-priority research targets for the next decade or so. Many of the research opportunities identified by these reports were defined through the efforts of the SEPM community, coordinated by workshops and initiatives (e.g., GeoSystems, Paleopedology, DETELON, and EARTHTIME), to articulate the most enduring scientific issues and associated challenges for the future. As the scientific research agenda has evolved so have the disciplinary boundaries of the scientific community, which now includes geochronologists, geochemists, geomorphologists, ecologists, microbiologists, atmospheric scientists, oceanographers, soil scientists, mathematicians and computer scientists. A singular intellectual challenge, echoed throughout the aforementioned publications, further unifies the broad array of interests and efforts of this diverse scientific community: A better understanding of how earth system processes respond, interact, and evolve over a range of climate states and conditions is pivotal to informing society on critical future issues including climate change, energy and water resources, landscape evolution and management, and ecosystem health and conservation under dynamic environmental conditions (Transitions 2012). The importance of broad-based and cross-disciplinary collaborations involving observation-based scientists and numerical modelers is now fully recognized as a means of realizing the potential of the sedimentary archive of dynamic earth system processes. As the new editors of the Sedimentary Record, we consider this publication forum as an opportunity to articulate the vision and recent discoveries behind this community momentum. We propose a series of articles over the next three years that highlight exciting research directions and that delineate the cultural and technological infrastructure that will be required to fully develop such opportunities and overcome their associated challenges. This article provides an introduction to the proposed journal series; your participation and feedback as to how the ‘Sedimentary Record of opportunities’ might evolve is strongly encouraged.

High-Spatial-Resolution Geochronology

Research Article| February 01, 2013 High-Spatial-Resolution Geochronology Alexander A. Nemchin; Alexander A. Nemchin 1Department of Applied Geology, Curtin UniversityPO Box U1987, Perth, WA 6845, AustraliaE-mail: A.Nemchin@curtin.edu.au Search for other works by this author on: GSW Google Scholar Matthew S. A. Horstwood; Matthew S. A. Horstwood 2NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, NG12 5GG, UKE-mail: msah@bgs.ac.uk Search for other works by this author on: GSW Google Scholar Martin J. Whitehouse Martin J. Whitehouse 3Swedish Museum of Natural HistoryBox 50007, SE104 05 Stockholm, Sweden Search for other works by this author on: GSW Google Scholar Author and Article Information Alexander A. Nemchin 1Department of Applied Geology, Curtin UniversityPO Box U1987, Perth, WA 6845, AustraliaE-mail: A.Nemchin@curtin.edu.au Matthew S. A. Horstwood 2NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, NG12 5GG, UKE-mail: msah@bgs.ac.uk Martin J. Whitehouse 3Swedish Museum of Natural HistoryBox 50007, SE104 05 Stockholm, Sweden Publisher: Mineralogical Society of America First Online: 09 Mar 2017 Online ISSN: 1811-5217 Print ISSN: 1811-5209 © 2013 by the Mineralogical Society of America Elements (2013) 9 (1): 31–37. https://doi.org/10.2113/gselements.9.1.31 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexander A. Nemchin, Matthew S. A. Horstwood, Martin J. Whitehouse; High-Spatial-Resolution Geochronology. Elements 2013;; 9 (1): 31–37. doi: https://doi.org/10.2113/gselements.9.1.31 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyElements Search Advanced Search Abstract High-spatial-resolution isotope analyses have revolutionised U–(Th–)Pb geochronology. These analyses can be done at scales of a few tens of microns or less using secondary ion mass spectrometry or laser ablation inductively coupled plasma mass spectrometry. They allow determination of the internal age variation of uranium- and thorium-bearing minerals and as a consequence much greater understanding of Earth system processes. The determination of variation on the micron scale necessitates the sampling of small volumes, which restricts the achievable precision but allows discrimination of discrete change, linkage to textural information, and determination of multiple isotopic and elemental data sets on effectively the same material. High-spatial-resolution analysis is being used in an increasing number of applications. Some of these applications have become fundamental to their scientific fields, while others have opened new opportunities for research. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The regional nature of global challenges: a need and strategy for integrated regional modeling

In this paper, we explore the regional nature of global environmental challenges. We take a broad approach by examining the scientific foundation that is needed to support policy and decision making and identifying some of the most important barriers to progress that are truly scale-dependent. In so doing, we hope to show that understanding global environmental changes requires understanding a number of intrinsically regional phenomena, and that successful decision making likewise requires an integrated approach that accounts for a variety of regional Earth system processes—which we define to include both human activities and environmental systems that operate or interact primarily at sub-continental scales. Understanding regional processes and phenomena, including regional decision-making processes and information needs, should thus be an integral part of the global change research agenda. To address some of the key issues and challenges, we propose an integrated regional modeling approach that accounts for the dynamic interactions among physical, ecological, biogeochemical, and human processes and provides relevant information to regional decision makers and stakeholders.

Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation

Uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. This reduction in carbon dioxide uptake was related to warming at the sea surface, which—according to model simulations—coincided with a reduction in the Atlantic meridional overturning circulation. The extent to which the slowdown of this circulation system—which transports warm surface waters to the northern high latitudes, and cool deep waters south—contributed to the reduction in carbon uptake has remained uncertain. Here, we use data on the oceanic transport of volume, heat and carbon dioxide to track carbon dioxide uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades. We separate anthropogenic carbon from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere, whereas the remaining is anthropogenic. We find that the uptake of anthropogenic carbon dioxide—released by human activities—occurred almost exclusively in the subtropical gyre. In contrast, natural carbon dioxide uptake—which results from natural Earth system processes—dominated in the subpolar gyre. We attribute the weakening of contemporary carbon dioxide uptake in the subpolar North Atlantic to a reduction in the natural component. We show that the slowdown of the meridional overturning circulation was largely responsible for the reduction in carbon uptake, through a reduction of oceanic heat loss to the atmosphere, and for the concomitant decline in anthropogenic CO2 storage in subpolar waters. Uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. An analysis of oceanographic data suggests that the slowdown of the meridional overturning circulation was largely responsible.

A history of give and take

Fossils of microorganisms from deep-sea sediment cores show that environmental change correlates closely with extinction but not with speciation, producing a nuanced view of the drivers of evolution. See Letter p.398 The fossil record is not a simple representation of the comings and goings of living things. There are interactions between life and Earth-system processes, and in this paper, Shanan Peters et al. describe how plate tectonics and climate change have together driven the extinction of planktonic foraminifera in the Atlantic basin throughout its history, beginning in the Jurassic. Major crises such as the end-Cretaceous mass extinction leave an imprint superimposed on this background. These factors have not, however, influenced the origin of new foraminifera species.

Double catastrophe: intermittent stratospheric geoengineering induced by societal collapse

Perceived failure to reduce greenhouse gas emissions has prompted interest in avoiding the harms of climate change via geoengineering, that is, the intentional manipulation of Earth system processes. Perhaps the most promising geoengineering technique is stratospheric aerosol injection (SAI), which reflects incoming solar radiation, thereby lowering surface temperatures. This paper analyzes a scenario in which SAI brings great harm on its own. The scenario is based on the issue of SAI intermittency, in which aerosol injection is halted, sending temperatures rapidly back toward where they would have been without SAI. The rapid temperature increase could be quite damaging, which in turn creates a strong incentive to avoid intermittency. In the scenario, a catastrophic societal collapse eliminates society’s ability to continue SAI, despite the incentive. The collapse could be caused by a pandemic, nuclear war, or other global catastrophe. The ensuing intermittency hits a population that is already vulnerable from the initial collapse, making for a double catastrophe. While the outcomes of the double catastrophe are difficult to predict, plausible worst-case scenarios include human extinction. The decision to implement SAI is found to depend on whether global catastrophe is more likely from double catastrophe or from climate change alone. The SAI double catastrophe scenario also strengthens arguments for greenhouse gas emissions reductions and against SAI, as well as for building communities that could be self-sufficient during global catastrophes. Finally, the paper demonstrates the value of integrative, systems-based global catastrophic risk analysis.

Coastal Zone Facing Climate Change: Knowledge Towards New Solutions

Humanity’s impact on the Earth system has become comparable to planetary-scale geological processes, such as ice ages. Consensus is growing that we have driven the planet into a new epoch, the Anthropocene, in which many Earth-system processes and the living fabric of ecosystems are now dominated by human activities. That the Earth has experienced large-scale, abrupt changes in the past indicates that it could experience similar changes in the future. This recognition has led researchers to take the first step to identify planetary and regional thresholds, and boundaries that, if crossed, could generate unacceptable environmental and social change [1]. Galvanized by the United Nations Conference on Environment and Development meeting of 1992, there has been a search for methods to build capacity of coastal nations and communities to manage their coastal and estuarine resources in a sustainable manner. Countries are now increasingly being affected mostly by hydro-meteorological hazards and disasters, namely, floods, mass movements (e.g. erosion, landslides and siltation), heat waves, wildfires, tropical cyclones, tsunamis, swells and dust storms [2,3]. Research now demonstrates that the continued functioning of the Earth system, as it has supported the well-being of human civilization in recent centuries is at risk. Without urgent action, we could face threats to water, food, biodiversity and other critical resources: these threats risk intensifying economic, ecological and social crises, creating the potential for a humanitarian emergency on a global scale. Nutrients are now the largest pollution problem in coastal marine ecosystems globally, and in the US, some 60% of estuaries are moderately to severely degraded, primarily from nutrients like nitrates and phosphates [4-7]. Developing economies tend to be dominated by resource-based activities with degrading and overexploitive uses of land, water and other coastal resources, with disruption of environmental processes through degradation of environmental quality and loss of critical terrestrial and aquatic habitats, leading to serious deleterious impacts on the health and productivity of coastal ecosystems. Studies have also showed that estuaries are particularly vulnerable to nutrient over-enrichment and trace metal contamination [8-12].

On the global geodetic observing system: Africa's preparedness and challenges

Space geodetic techniques and satellite missions play a crucial role in the determination and monitoring of geo-kinematics, Earth's rotation and gravity fields. These three pillars of geodesy provide the basis for determining the geodetic reference frames with high accuracy, spatial resolution and temporal stability. Space geodetic techniques have been used for the assessment of geo-hazards, anthropogenic hazards and in the design of early warning systems for hazard and disasters. In general, space geodesy provides products for Earth observation, science and influences many activities (e.g., building and management) in a modern society. In order to further promote the application of space geodetic methods to solving Earth science problems, the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) was commissioned as an important geodetic infrastructure that integrates different geodetic techniques (such as Global Navigation Satellite Systems, Very Long Baseline Interferometry, Satellite Laser Ranging, Interferometric Synthetic Aperture Radar and Doppler Orbitography and Radio-positioning Integrated by Satellite), models and analysis techniques for the purpose of ensuring long-term, precise monitoring of geodetic observables vital for monitoring Earth system processes. Since its inception, there has been considerable progress made towards setting up the infrastructure necessary for the establishment of the GGOS database. While the challenges that beleaguer the GGOS are acknowledged (at least at global level), the assessment of an attuned GGOS infrastructure in the African context is necessary, yet lacking. In the present contribution, (a) the African preparedness and response to the observing system is assessed, and (b) the specific scientific and technological challenges of establishing a regional GGOS hub for Africa are reviewed. Currently only South Africa has a fundamental geodetic observatory located at Hartebeesthoek, Pretoria. Other countries in Africa have shown interest to participate in global geodetic activities, in particular through interest in the development of a unified African geodetic reference frame (AFREF). In particular interest has been shown in the proposed African VLBI Network (AVN), which will be partially based on existing ex-telecommunication radio antennas. Several countries are investigating their participation in the AVN, including Kenya, Nigeria and Ghana.