Description: Recent revisions of phosphate rock reserves and resources: a critique Earth System Dynamics, 5, 491-507, 2014 Author(s): J. D. Edixhoven, J. Gupta, and H. H. G. Savenije Phosphate rock (PR) is a finite mineral indispensable for fertilizer production, while P (phosphorus) is a major pollutant if applied or discharged in excess, causing widespread eutrophication (Carpenter and Bennet, 2011). High-grade PR is obtained from deposits which took millions of years to form and which are gradually being depleted. Recently, global PR reserves as reported by the US Geological Survey (USGS) have increased from 16 000 Mt PR in 2010 to 65 000 Mt PR in 2011 and further to 67 000 Mt PR in 2014. The majority of this 4-fold increase is based on a 2010 report by the International Fertilizer Development Center (IFDC), which increased Moroccan reserves from 5700 Mt PR as reported by USGS, to 51 000 Mt PR, reported as upgraded ("beneficiated") concentrate. The report also increased global resources from 163 000 Mt PR reported in the literature in 1989 to 290 000 Mt PR. IFDC used a simplified resource terminology which does not use the underlying thresholds for reserves and resources used in the USGS classification. IFDC proposed that agreement should be reached on PR resource terminology which should be as simple as possible. The report has profoundly influenced the PR scarcity debate, shifting the emphasis from resource scarcity to the pollution angle of the phosphate problem. In view of the high dependence of food production on PR and the importance of data on PR reserves and resources for scientific analysis and policy making, data on PR deposits should be transparent, comparable, reliable, and credible. We analyze (i) how IFDC's simplified terminology compares to international best practice in resource classification and whether it is likely to yield data that meet these requirements, (ii) whether the difference in volume between raw PR ore and upgraded PR concentrate is sufficiently noted in the literature, and (iii) whether the IFDC report presents an accurate picture of PR reserves and resources. We conclude that, while there is a global development toward common criteria in resource reporting, IFDC's lack of clear thresholds for reserves and resources contravenes this and that the vagueness of its definitions for reserves and resources may allow deposits to be termed reserves or resources which could not be recognized as such under leading mineral resource classifications. The difference between PR ore and PR concentrate is barely noted in the literature, causing pervasive confusion and a significant degree of error in many assessments. Finally, we find that the report most likely presents an inflated picture of global reserves, in particular those of Morocco, where the aggregate resources of three of the four Moroccan/Western Saharan major PR deposits appear to have been simply converted to "reserves". Following the release of the IFDC report, various analysts have concluded or suggested that the available PR deposits or even the currently reported resources would likely last several thousands of years at current consumption rates. However, the data on which these statements were based do not appear to warrant such a conclusion. Further research is required as to the quantity of PR deposits and their viability for future extraction, using uniform and transparent classification terminology.

Description: Contrasting roles of interception and transpiration in the hydrological cycle – Part 2: Moisture recycling Earth System Dynamics, 5, 471-489, 2014 Author(s): R. J. van der Ent, L. Wang-Erlandsson, P. W. Keys, and H. H. G. Savenije The contribution of land evaporation to local and remote precipitation (i.e. moisture recycling) is of significant importance to sustain water resources and ecosystems. But how important are different evaporation components in sustaining precipitation? This is the first paper to present moisture recycling metrics for partitioned evaporation. In the companion paper Wang-Erlandsson et al. (2014) (hereafter Part 1), evaporation was partitioned into vegetation interception, floor interception, soil moisture evaporation and open-water evaporation (constituting the direct, purely physical fluxes, largely dominated by interception), and transpiration (delayed, biophysical flux). Here, we track these components forward as well as backward in time. We also include age tracers to study the atmospheric residence times of these evaporation components. We present a new image of the global hydrological cycle that includes quantification of partitioned evaporation and moisture recycling as well as the atmospheric residence times of all fluxes. We demonstrate that evaporated interception is more likely to return as precipitation on land than transpired water. On average, direct evaporation (essentially interception) is found to have an atmospheric residence time of 8 days, while transpiration typically resides for 9 days in the atmosphere. The process scale over which evaporation recycles is more local for interception compared to transpiration; thus interception generally precipitates closer to its evaporative source than transpiration, which is particularly pronounced outside the tropics. We conclude that interception mainly works as an intensifier of the local hydrological cycle during wet spells and wet seasons. On the other hand, transpiration remains active during dry spells and dry seasons and is transported over much larger distances downwind, where it can act as a significant source of moisture. Thus, as various land-use types can differ considerably in their partitioning between interception and transpiration, our results stress that land-use changes (e.g. forest-to-cropland conversion) do not only affect the magnitude of moisture recycling, but could also influence the moisture recycling patterns and lead to a redistribution of water resources. As such, this research highlights that land-use changes can have complex effects on the atmospheric branch of the hydrological cycle.

Description: Contrasting roles of interception and transpiration in the hydrological cycle – Part 1: Temporal characteristics over land Earth System Dynamics, 5, 441-469, 2014 Author(s): L. Wang-Erlandsson, R. J. van der Ent, L. J. Gordon, and H. H. G. Savenije Moisture recycling, the contribution of terrestrial evaporation to precipitation, has important implications for both water and land management. Although terrestrial evaporation consists of different fluxes (i.e. transpiration, vegetation interception, floor interception, soil moisture evaporation, and open-water evaporation), moisture recycling (terrestrial evaporation–precipitation feedback) studies have up to now only analysed their combined total. This paper constitutes the first of two companion papers that investigate the characteristics and roles of different evaporation fluxes for land–atmosphere interactions. Here, we investigate the temporal characteristics of partitioned evaporation on land and present STEAM (Simple Terrestrial Evaporation to Atmosphere Model) – a hydrological land-surface model developed to provide inputs to moisture tracking. STEAM estimates a mean global terrestrial evaporation of 73 900 km 3 year -1 , of which 59% is transpiration. Despite a relatively simple model structure, validation shows that STEAM produces realistic evaporative partitioning and hydrological fluxes that compare well with other global estimates over different locations, seasons, and land-use types. Using STEAM output, we show that the terrestrial residence timescale of transpiration (days to months) has larger inter-seasonal variation and is substantially longer than that of interception (hours). Most transpiration occurs several hours or days after a rain event, whereas interception is immediate. In agreement with previous research, our simulations suggest that the vegetation's ability to transpire by retaining and accessing soil moisture at greater depth is critical for sustained evaporation during the dry season. We conclude that the differences in temporal characteristics between evaporation fluxes are substantial and reasonably can cause differences in moisture recycling, which is investigated more in the companion paper (van der Ent et al., 2014, hereafter Part 2).

Description: Continued increase in atmospheric CO 2 seasonal amplitude in the 21st century projected by the CMIP5 Earth system models Earth System Dynamics, 5, 423-439, 2014 Author(s): F. Zhao and N. Zeng In the Northern Hemisphere, atmospheric CO 2 concentration declines in spring and summer, and rises in fall and winter. Ground-based and aircraft-based observation records indicate that the amplitude of this seasonal cycle has increased in the past. Will this trend continue in the future? In this paper, we analyzed simulations for historical (1850–2005) and future (RCP8.5, 2006–2100) periods produced by 10 Earth system models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Our results present a model consensus that the increase of CO 2 seasonal amplitude continues throughout the 21st century. Multi-model ensemble relative amplitude of detrended global mean CO 2 seasonal cycle increases by 62 ± 19% in 2081–2090, compared to 1961–1970. This amplitude increase corresponds to a 68 ± 25% increase in net biosphere production (NBP). The results show that the increase of NBP amplitude mainly comes from enhanced ecosystem uptake during Northern Hemisphere growing season under future CO 2 and temperature conditions. Separate analyses on net primary production (NPP) and respiration reveal that enhanced ecosystem carbon uptake contributes about 75% of the amplitude increase. Stimulated by higher CO 2 concentration and high-latitude warming, enhanced NPP likely outcompetes increased respiration at higher temperature, resulting in a higher net uptake during the northern growing season. The zonal distribution and spatial pattern of NBP change suggest that regions north of 45° N dominate the amplitude increase. Models that simulate a stronger carbon uptake also tend to show a larger increase of NBP seasonal amplitude, and the cross-model correlation is significant ( R =0.73, p 〈 0.05).

Description: Path independence of climate and carbon cycle response over a broad range of cumulative carbon emissions Earth System Dynamics, 5, 409-422, 2014 Author(s): T. Herrington and K. Zickfeld Recent studies have identified an approximately proportional relationship between global warming and cumulative carbon emissions, yet the robustness of this relationship has not been tested over a broad range of cumulative emissions and emission rates. This study explores the path dependence of the climate and carbon cycle response using an Earth system model of intermediate complexity forced with 24 idealized emissions scenarios across five cumulative emission groups (1275–5275 Gt C) with varying rates of emission. We find the century-scale climate and carbon cycle response after cessation of emissions to be approximately independent of emission pathway for all cumulative emission levels considered. The ratio of global mean temperature change to cumulative emissions – referred to as the transient climate response to cumulative carbon emissions (TCRE) – is found to be constant for cumulative emissions lower than ∼1500 Gt C but to decline with higher cumulative emissions. The TCRE is also found to decrease with increasing emission rate. The response of Arctic sea ice is found to be approximately proportional to cumulative emissions, while the response of the Atlantic Meridional Overturning Circulation does not scale linearly with cumulative emissions, as its peak response is strongly dependent on emission rate. Ocean carbon uptake weakens with increasing cumulative emissions, while land carbon uptake displays non-monotonic behavior, increasing up to a cumulative emission threshold of ∼2000 Gt C and then declining.

Description: Climate impact research: beyond patchwork Earth System Dynamics, 5, 399-408, 2014 Author(s): V. Huber, H. J. Schellnhuber, N. W. Arnell, K. Frieler, A. D. Friend, D. Gerten, I. Haddeland, P. Kabat, H. Lotze-Campen, W. Lucht, M. Parry, F. Piontek, C. Rosenzweig, J. Schewe, and L. Warszawski Despite significant progress in climate impact research, the narratives that science can presently piece together of a 2, 3, 4, or 5 °C warmer world remain fragmentary. Here we briefly review past undertakings to characterise comprehensively and quantify climate impacts based on multi-model approaches. We then report on the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), a community-driven effort to compare impact models across sectors and scales systematically, and to quantify the uncertainties along the chain from greenhouse gas emissions and climate input data to the modelling of climate impacts themselves. We show how ISI-MIP and similar efforts can substantially advance the science relevant to impacts, adaptation and vulnerability, and we outline the steps that need to be taken in order to make the most of the available modelling tools. We discuss pertinent limitations of these methods and how they could be tackled. We argue that it is time to consolidate the current patchwork of impact knowledge through integrated cross-sectoral assessments, and that the climate impact community is now in a favourable position to do so.

Description: Mechanism for potential strengthening of Atlantic overturning prior to collapse Earth System Dynamics, 5, 383-397, 2014 Author(s): D. Ehlert and A. Levermann The Atlantic meridional overturning circulation (AMOC) carries large amounts of heat into the North Atlantic influencing climate regionally as well as globally. Palaeo-records and simulations with comprehensive climate models suggest that the positive salt-advection feedback may yield a threshold behaviour of the system. That is to say that beyond a certain amount of freshwater flux into the North Atlantic, no meridional overturning circulation can be sustained. Concepts of monitoring the AMOC and identifying its vicinity to the threshold rely on the fact that the volume flux defining the AMOC will be reduced when approaching the threshold. Here we advance conceptual models that have been used in a paradigmatic way to understand the AMOC, by introducing a density-dependent parameterization for the Southern Ocean eddies. This additional degree of freedom uncovers a mechanism by which the AMOC can increase with additional freshwater flux into the North Atlantic, before it reaches the threshold and collapses: an AMOC that is mainly wind-driven will have a constant upwelling as long as the Southern Ocean winds do not change significantly. The downward transport of tracers occurs either in the northern sinking regions or through Southern Ocean eddies. If freshwater is transported, either atmospherically or via horizontal gyres, from the low to high latitudes, this would reduce the eddy transport and by continuity increase the northern sinking which defines the AMOC until a threshold is reached at which the AMOC cannot be sustained. If dominant in the real ocean this mechanism would have significant consequences for monitoring the AMOC.

Description: Impact of the Atlantic Multidecadal Oscillation (AMO) on deriving anthropogenic warming rates from the instrumental temperature record Earth System Dynamics, 5, 375-382, 2014 Author(s): G. R. van der Werf and A. J. Dolman The instrumental surface air temperature record has been used in several statistical studies to assess the relative role of natural and anthropogenic drivers of climate change. The results of those studies varied considerably, with anthropogenic temperature trends over the past 25–30 years suggested to range from 0.07 to 0.20 °C decade −1 . In this short communication, we assess the origin of these differences and highlight the inverse relation between the temperature trend of the past 30 years and the weight given to the Atlantic Multidecadal Oscillation (AMO) as an explanatory factor in the multiple linear regression (MLR) tool that is usually employed. We highlight that robust MLR outcomes require a better understanding of the AMO in general and, more specifically, of its characterization. Our results indicate that both the high and the low end of the anthropogenic trend over the past 30 years found in previous studies are unlikely and that a transient climate response of 1.6 (1.0–3.3) °C best captures the historic instrumental temperature record.

Description: Climate impacts on human livelihoods: where uncertainty matters in projections of water availability Earth System Dynamics, 5, 355-373, 2014 Author(s): T. K. Lissner, D. E. Reusser, J. Schewe, T. Lakes, and J. P. Kropp Climate change will have adverse impacts on many different sectors of society, with manifold consequences for human livelihoods and well-being. However, a systematic method to quantify human well-being and livelihoods across sectors is so far unavailable, making it difficult to determine the extent of such impacts. Climate impact analyses are often limited to individual sectors (e.g. food or water) and employ sector-specific target measures, while systematic linkages to general livelihood conditions remain unexplored. Further, recent multi-model assessments have shown that uncertainties in projections of climate impacts deriving from climate and impact models, as well as greenhouse gas scenarios, are substantial, posing an additional challenge in linking climate impacts with livelihood conditions. This article first presents a methodology to consistently measure what is referred to here as AHEAD (Adequate Human livelihood conditions for wEll-being And Development). Based on a trans-disciplinary sample of concepts addressing human well-being and livelihoods, the approach measures the adequacy of conditions of 16 elements. We implement the method at global scale, using results from the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) to show how changes in water availability affect the fulfilment of AHEAD at national resolution. In addition, AHEAD allows for the uncertainty of climate and impact model projections to be identified and differentiated. We show how the approach can help to put the substantial inter-model spread into the context of country-specific livelihood conditions by differentiating where the uncertainty about water scarcity is relevant with regard to livelihood conditions – and where it is not. The results indicate that livelihood conditions are compromised by water scarcity in 34 countries. However, more often, AHEAD fulfilment is limited through other elements. The analysis shows that the water-specific uncertainty ranges of the model output are outside relevant thresholds for AHEAD for 65 out of 111 countries, and therefore do not contribute to the overall uncertainty about climate change impacts on livelihoods. In 46 of the countries in the analysis, water-specific uncertainty is relevant to AHEAD. The AHEAD method presented here, together with first results, forms an important step towards making scientific results more applicable for policy decisions.

Description: Explaining the seasonal cycle of the globally averaged CO 2 with a carbon-cycle model Earth System Dynamics, 5, 345-354, 2014 Author(s): G. A. Alexandrov The seasonal changes in the globally averaged atmospheric carbon-dioxide concentrations reflect an important aspect of the global carbon cycle: the gas exchange between the atmosphere and terrestrial biosphere. The data on the globally averaged atmospheric carbon-dioxide concentrations, which are reported by Earth System Research Laboratory of the US National Oceanic & Atmospheric Administration (NOAA/ESRL), could be used to demonstrate the adequacy of the global carbon-cycle models. However, it was recently found that the observed amplitude of seasonal variations in the atmospheric carbon-dioxide concentrations is higher than simulated. In this paper, the factors that affect the amplitude of seasonal variations are explored using a carbon-cycle model of reduced complexity. The model runs show that the low amplitude of the simulated seasonal variations may result from underestimated effect of substrate limitation on the seasonal pattern of heterotrophic respiration and from an underestimated magnitude of the annual gross primary production (GPP) in the terrestrial ecosystems located to the north of 25° N.