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  • Articles  (545)
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  • Articles  (545)
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  • 1
    Publication Date: 2019-09-20
    Description: Current global mitigation ambition as under the Paris Agreement as reflected in the National Determined Contributions (NDCs) up to 2030 is insufficient to achieve the Agreement's 1.5 °C long term temperature limit. As governments are preparing new and updated NDCs for 2020, the question as to how much collective improvement is achieved is a pivotal one for the credibility of the international climate regime. The recent Special Report of the Intergovernmental Panel of Climate Change on Global Warming of 1.5 °C has assessed a wide range of scenarios that achieve the 1.5 °C limit. Those pathways are characterized by a substantial increase in near-term action and total greenhouse gas (GHG) emission levels about 50 % lower than what is implied by current NDCs. Here we assess the outcomes of different scenarios of NDC updating that fall short of achieving this 1.5 °C benchmark. We find that incremental improvements in reduction targets even if achieved globally, are insufficient to align collective ambition with the goals of the Paris Agreement. We provide estimates for global mean temperature increase by 2100 for different incremental NDC update scenarios and illustrate climate impacts under those scenarios including for extreme temperature, long-term sea level rise and economic damages for the most vulnerable countries. Under the assumption of maintaining ambition as reflected in current NDCs up to 2100 and beyond, we project a reduction in the Gross Domestic Product (GDP) in tropical countries of about 50–60 % compared to a no-climate change scenario and long-term sea-level rise of close to 2 m in 2300. About half of these impacts can be avoided by limiting warming to 1.5 °C, or below. Scenarios of more incremental NDC improvements do not lead to comparable reductions in climate impacts. An increase in 2030 of the aggregated NDC ambition of big emitters by 33 % does not deliver more than about half the potential reduction in climate impacts compared to limiting warming to 1.5 °C. Our results underscore that a transformational increase in 2030 ambition is required to achieve the goals of the Paris Agreement and avoid the worst impacts of climate change.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
    Publication Date: 2019-09-09
    Description: Under variable and changing climates groundwater storage sustains vital ecosystems and enables freshwater withdrawals globally for agriculture, drinking-water, and industry. Here, we assess recent changes in groundwater storage (ΔGWS) from 2002 to 2016 in 37 of the world's large aquifer systems using an ensemble of datasets from the Gravity Recovery and Climate Experiment (GRACE) and Land Surface Models (LSMs). Ensemble GRACE-derived ΔGWS is well reconciled to in-situ observations (r = 0.62–0.86, p value  0.5, p value  90th percentile, 1901–2016) precipitation and is inconsistent with prevailing narratives of global-scale groundwater depletion. Substantial uncertainty remains in estimates of GRACE-derived ΔGWS, evident from 20 realisations presented here, but these data provide a regional context to changes in groundwater storage observed more locally through piezometry.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
    Publication Date: 2019-09-05
    Description: This paper aims to address the continuous debate of whether a hiatus occurred in the turn of this century. Several models have been employed to fit the global mean surface temperature data, and the results suggest that the allegation of an occurrence of hiatus lacks statistical evidence. However, these models had potential deficiencies in their capacity for detecting breakpoints, thereby weakening the arguments that deny the existence of a hiatus. To address this issue, we propose an improved sparse representation model, which can automatically segment and fit temperature records using piecewise polynomials. Simulations revealed improved detection performance; studies on five prominent global temperature records produced 2 to 6 breakpoints, none of which occurred after the year 1976, thus reinforcing arguments denying the existence of a 20th century hiatus.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 4
    Publication Date: 2019-09-03
    Description: The effect of Glacial Isostatic Adjustment (GIA) on the shape and gravity of the Earth is usually described by numerical models that simultaneously solve for glacial evolution and Earth's rheology, being mainly constrained by the geological evidence of local ice extent and global sea level, as well as by geodetic observations of Earth's rotation. In recent years, GPS and GRACE observations have often been used to improve those models, especially in the context of regional studies. However, consistency issues between different regional models limit their ability to answer questions from global scale geodesy. Examples are the closure of the sea level budget, the explanation of observed changes in Earth's rotation, and the determination of the origin of the Earth's reference frame. Here, we present a global empirical model of present-day GIA, solely based on GRACE data and on geoid fingerprints of mass redistribution. We will show how the use of observations from a single space-borne platform, together with GIA fingerprints based on different viscosity profiles, allows us to tackle the questions from global scale geodesy mentioned above. We find that, in the GRACE era (2003–2016), freshwater exchange between land and oceans has caused global mean sea level to rise by 1.5 ± 0.3 mm/yr, the geocentre to move by 0.5 mm/yr, and the Earth's dynamic oblateness (J2) to increase by 6.7 × 10−11/yr.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
    Publication Date: 2019-09-02
    Description: Widespread flooding events are among the major natural hazards in Central Europe. Such events are usually related to intensive, long-lasting precipitation. Despite some prominent floods during the last three decades (e.g. 1997, 1999, 2002, and 2013), extreme floods are rare and associated with estimated long return periods of more than 100 years. To assess the associated risks of such extreme events, reliable statistics of precipitation and discharge are required. Comprehensive observations, however, are mainly available for the last 50–60 years or less. This shortcoming can be reduced using stochastic data sets. One possibility towards this aim is to consider climate model data or extended reanalyses. This study presents and discusses a validation of different century-long data sets, a large ensemble of decadal hindcasts, and also projections for the upcoming decade. Global reanalysis for the 20th century with a horizontal resolution of more than 100 km have been dynamically downscaled with a regional climate model (COSMO-CLM) towards a higher resolution of 25 km. The new data sets are first filtered using a dry-day adjustment. The simulations show a good agreement with observations for both statistical distributions and time series. Differences mainly appear in areas with sparse observation data. The temporal evolution during the past 60 years is well captured. The results reveal some long-term variability with phases of increased and decreased heavy precipitation. The overall trend varies between the investigation areas but is significant. The projections for the upcoming decade show ongoing tendencies with increased precipitation for upper percentiles. The presented RCM ensemble not only allows for more robust statistics in general, in particular it is suitable for a better estimation of extreme values.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 6
    Publication Date: 2019-08-20
    Description: This study uses the high resolution outputs of the recent CORDEX-AFRICA climate projections to investigate the future changes in different aspects of the hydrological cycle over West Africa. Over the twenty-first century, temperatures in West Africa are expected to increase at a faster rate (+ 0.5 °C per decade) than the global average (+ 0.3 °C per decade), and mean precipitation is expected to increase over the Guinea Coast (+ 0.03 mm/day per decade) but decrease over the Sahel (− 0.005 mm/day per decade). In addition, precipitation is expected to become more intense (+ 0.2 mm/day per decade) and less frequent (− 1.5 days per decade) over the entire West Africa as a results of increasing regional temperature (precipitation intensity increases on average by + 0.35 mm/day per °C and precipitation frequency decreases on average by − 2.2 days per °C). Over the Sahel, the average length of dry spells is also expected to increase with temperature (+ 4 % days per °C), which increases the likelihood for droughts with warming in this sub-region. Hence, the hydrological cycle is expected to increase throughout the twenty-first century over the entire West Africa, on average by + 11 % per °C over the Sahel as a result of increasing precipitation intensity and lengthening of dry spells, and on average by + 3 % per °C over the Guinea Coast as a result of increasing precipitation intensity only.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
    Publication Date: 2019-08-15
    Description: A future of increasing atmospheric carbon dioxide concentrations, changing climate, growing human populations, and shifting socioeconomic conditions means that the global agricultural system will need to adapt in order to feed the world. These changes will affect not only agricultural land, but terrestrial ecosystems in general. Here, we use the coupled land use and vegetation model LandSyMM to quantify future land use change and resulting impacts on ecosystem service indicators including carbon sequestration, runoff, and nitrogen pollution. We additionally hold certain variables, such as climate or land use, constant to assess the relative contribution of different drivers to the projected impacts. While indicators of some ecosystem services (e.g., flood and drought risk) see trends that are mostly dominated by the direct effects of climate change, others (e.g., carbon sequestration) depend critically on land use and management. Scenarios in which climate change mitigation is more difficult (Shared Socioeconomic Pathways 3 and 5) have the strongest impacts on ecosystem service indicators, such as a loss of 13–19 % of land in biodiversity hotspots and a 28 % increase in nitrogen pollution. Evaluating a suite of ecosystem service indicators across scenarios enables the identification of tradeoffs and co-benefits associated with different climate change mitigation and adaptation strategies and socioeconomic developments.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 8
    Publication Date: 2019-08-09
    Description: Energy balance models (EBM) are highly simplified systems of the climate system. The global temperature is calculated by the radiation budget through the incoming energy from the Sun and the outgoing energy from the Earth. The argument that the temperature can be calculated by the simple radiation budget is revisited. The underlying assumption for a realistic temperature distribution is explored: One has to assume a moderate diurnal cycle due to the large heat capacity and the fast rotation of the Earth. Interestingly, the global mean in the revised EBM is very close to the originally proposed value. The time dependent-EBM predicts a flat meridional temperature gradient for large heat capacities which can be related to very effective vertical diffusion. Motivated by this finding, sensitivity experiments with a complex model are performed where the vertical diffusion in the ocean has been increased. The resulting climate shows a flat meridional temperature gradient and a deeper thermocline. The common pattern of surface temperature anomalies and climate reconstructions suggests a possible mechanism for past climate changes prior to 3 million years ago.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
    Publication Date: 2019-08-08
    Description: The influence of climatic change on the carbon cycle is important as part of a CO2-climate feedback loop. However the magnitude of the coupling depends on the timescales involved. We expand on previous analyses of the ice-core CO2 data from the pre-industrial period 1000–1750, extending the analysis into the 20th century. Our results emphasise the limitations of characterising the climate-to-CO2 influence by a single number γ. Even once a time-scale dependence is incorporated, the coldest part of the Little Ice Age seems to reflect different behaviour to that in earlier or later centuries. Different temperature reconstructions appear to capture distinct aspects of pre-industrial climate fluctuations that lacked global coherence. An exploratory study extends the analysis into the industrial period. In this study, most paleo-temperature data fail to fit the plateau (or plateaus) in 20th century ice-core CO2, with one particular reconstruction as an exception. One interpretation of this fit is that although the reconstruction does not closely reflect hemispheric temperature changes, it samples a pattern of variation where the terrestrial carbon exchange is anomalously sensitive to regional climate variations. These various results suggest that this type of empirical study may have limited applicability to the 21st century.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
    Publication Date: 2019-08-08
    Description: In 2015, El Niño caused severe droughts in equatorial Asia (EA). The severe droughts enhanced fire activities in the dry seasons, leading to massive fire emissions of CO2 and aerosols. Using large event attribution ensembles of the MIROC5 atmospheric global climate model, we suggest that historical anthropogenic warming increased the chances of meteorological droughts exceeding the 2015 observations in the EA area. Large probability increases in stronger droughts than the 2015 event are found in the ensemble simulations of 1.5 °C and 2.0 °C global warming according to the Paris Agreement goals. Further drying is projected in the 3.0 °C ensemble. We combine these experiments and empirical functions between precipitation, burned area, and fire emissions of CO2 and PM2.5. Increases in the chances of the burned area and the emissions of CO2 and PM2.5 exceeding the 2015 observations due to anthropogenic climate change in the past are not significant. In contrast, there are significant increases in the burned area and CO2 and PM2.5 emissions even if the 1.5 °C and 2.0 °C goals are achieved. If global warming reaches 3.0 °C, as is expected from the current mitigation policies of nations, the chances of the burned area, CO2 and PM2.5 emissions exceeding the 2015 observed values become approximately 100 %, at least in the single model ensembles. We also compare changes in fire CO2 emissions due to climate changes and the land-use CO2 emission scenarios of five shared socio-economic pathways, where the climate change effects on fire are not considered. There are two main implications. First, in a national policy context, future EA climate policy will need to consider these climate change effects regarding both mitigation and adaptation aspects. Second, the consideration of fire increases would change global CO2 emissions and the mitigation strategy, which suggests that future climate change mitigation studies should take these factors into account.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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