Variability Of Carbon Cycle Research Articles

Ecosystem functioning is enveloped by hydrometeorological variability.

Terrestrial ecosystem processes, and the associated vegetation carbon dynamics, respond differently to hydrometeorological variability across timescales, and so does our scientific understanding of the underlying mechanisms. Long-term variability of the terrestrial carbon cycle is not yet well constrained and the resulting climate-biosphere feedbacks are highly uncertain. Here we present a comprehensive overview of hydrometeorological and ecosystem variability from hourly to decadal timescales integrating multiple in situ and remote-sensing datasets characterizing extra-tropical forest sites. We find that ecosystem variability at all sites is confined within a hydrometeorological envelope across sites and timescales. Furthermore, ecosystem variability demonstrates long-term persistence, highlighting ecological memory and slow ecosystem recovery rates after disturbances. However, simulation results with state-of-the-art process-based models do not reflect this long-term persistent behaviour in ecosystem functioning. Accordingly, we develop a cross-time-scale stochastic framework that captures hydrometeorological and ecosystem variability. Our analysis offers a perspective for terrestrial ecosystem modelling and paves the way for new model-data integration opportunities in Earth system sciences.

Climate controls over the net carbon uptake period and amplitude of net ecosystem production in temperate and boreal ecosystems

The seasonal and interannual variability of the terrestrial carbon cycle is regulated by the interactions of climate and ecosystem function. However, the key factors and processes determining the interannual variability of net ecosystem productivity (NEP) in different biomes are far from clear. Here, we quantified yearly anomalies of seasonal and annual NEP, net carbon uptake period (CUP), and the maximum daily NEP (NEPmax) in response to climatic variables in 24 deciduous broadleaf forest (DBF), evergreen forest (EF), and grassland (GRA) ecosystems that include at least eight years of eddy covariance observations. Over the 228 site-years studied, interannual variations in NEP were mostly explained by anomalies of CUP and NEPmax. CUP was determined by spring and autumn net carbon uptake phenology, which were sensitive to annual meteorological variability. Warmer spring temperatures led to an earlier start of net carbon uptake activity and higher spring and annual NEP values in DBF and EF, while warmer autumn temperatures in DBF, higher autumn radiation in EF, and more summer and autumn precipitation in GRA resulted in a later ending date of net carbon uptake and associated higher autumn and annual NEP. Anomalies in NEPmax s were determined by summer precipitation in DBF and GRA, and explained more than 50% of variation in summer NEP anomalies for all the three biomes. Results demonstrate the role of meteorological variability in controlling CUP and NEPmax, which in turn help describe the seasonal and interannual variability of NEP.

Scaled-dependence and seasonal variations of carbon cycle through development of an advanced eco-hydrologic and biogeochemical coupling model

Recent research has shown that inland water may play some role in carbon cycling, although the extent of its contribution has remained uncertain due to the limited amount of reliable data available. In this study, the author developed a new model coupling original eco-hydrology model and five biogeochemical cycle models (NICE-BGC), which incorporates complex coupling of hydrologic-carbon cycle in terrestrial-aquatic linkages and interplay between inorganic and organic carbon during the whole process of carbon cycling. This improved model was applied to Eurasian wetland by using three types of river network data to evaluate scaled-dependence of carbon cycle there. The model improved accuracy of low pH and alkalinity and DOC flux increase in the wetland in the northern part of study area with the finer river network data. The model showed that the difference in the carbon flux between different river network data becomes larger in downstream region, and that this difference is more predominant in the stream channel than in the hillslope, implying the importance of dry watercourses and intermittent rivers. The model was then extended to the global scale to evaluate seasonal variations of carbon cycle both in hillslope and river. The result extended from the previous studies to clarify that; (i) soil temperature has some effect on the carbon transport by biologic process responsible for carbon production in addition to clear relationship between runoff and carbon export, (ii) the high runoff during April to June and the large DOC and POC flux (about 458.38±474.41 TgC/season and 239.25±289.90 TgC/season) during January to March in hillslope, (iii) CO2 evasion becomes maximum about 294.66±93.80 TgC/season during January to June primarily affected by Amazon River, and (iv) sediment storage is larger and takes about 76.80±13.19 TgC/season during July to September particularly in Asian and North American rivers. This scaled-dependence and seasonal variations of carbon cycle helps to bridge the gap between carbon transport to the longitudinal direction and gas emission to the atmosphere in previous researches. This simulation system would also help for the further field observations, remotely-sensed imagery, and satellite datasets, and play important role in improvement in biogeochemical activity in spatio-temporal hot spots.

Global marine biogeochemical reanalyses assimilating two different sets of merged ocean colour products

The only observations of marine biogeochemistry with routine global coverage are satellite ocean colour, which provide measurements of ocean bio-optical properties, with coverage still incomplete and limited to the sea surface. Models are therefore required to provide full spatial coverage, and through data assimilation can be combined with observations to create a reanalysis. This can then be used to investigate both observed and non-observed variables, including those relating to the carbon cycle. As part of the Climate Modelling User Group (CMUG) within the European Space Agency's Climate Change Initiative (CCI) project, two global marine biogeochemical reanalyses have been produced by assimilating ocean colour-derived chlorophyll data into a coupled physical-biogeochemical ocean model over the period September 1997 to July 2012. One reanalysis assimilated CCI products, the other assimilated GlobColour products, with a non-assimilative hindcast run for comparison. Each has been validated against independent in situ observations of chlorophyll, nutrients and carbon cycle variables. The assimilation of either source of ocean colour data was found to improve the model's representation of chlorophyll concentration throughout the water column, including the frequency and positioning of deep chlorophyll maxima. The assimilation also resulted in a slight improvement in nutrient concentrations and surface fugacity of carbon dioxide compared with in situ observations, although the overall impact on mean fields was small. This was found to be due in part to cancelling errors within the model, with the assimilation providing information on model biases, which can be used to inform future climate model development. The reanalyses were also able to reproduce expected seasonal cycles, as well as inter-annual variability related to major climate drivers. This study concludes that both CCI and GlobColour products are suitable for assimilation purposes, and that assimilating ocean colour data is of clear benefit.

Interannual variability in Australia's terrestrial carbon cycle constrained by multiple observation types

Abstract. Recent studies have shown that semi-arid ecosystems in Australia may be responsible for a significant part of the interannual variability in the global concentration of atmospheric carbon dioxide. Here we use a multiple constraints approach to calibrate a land surface model of Australian terrestrial carbon and water cycles, with a focus on interannual variability. We use observations of carbon and water fluxes at 14 OzFlux sites, as well as data on carbon pools, litterfall and streamflow. We include calibration of the function describing the response of heterotrophic respiration to soil moisture. We also explore the effect on modelled interannual variability of parameter equifinality, whereby multiple combinations of parameters can give an equally acceptable fit to the calibration data. We estimate interannual variability of Australian net ecosystem production (NEP) of 0.12–0.21 PgC yr−1 (1σ) over 1982–2013, with a high anomaly of 0.43–0.67 PgC yr−1 in 2011 relative to this period associated with exceptionally wet conditions following a prolonged drought. The ranges are due to the effect on calculated NEP anomaly of parameter equifinality, with similar contributions from equifinality in parameters associated with net primary production (NPP) and heterotrophic respiration. Our range of results due to parameter equifinality demonstrates how errors can be underestimated when a single parameter set is used.

Carbon cycle responses of semi-arid ecosystems to positive asymmetry in rainfall.

Recent evidence shows that warm semi-arid ecosystems are playing a disproportionate role in the interannual variability and greening trend of the global carbon cycle given their mean lower productivity when compared with other biomes (Ahlström etal. 2015 Science, 348, 895). Using multiple observations (land-atmosphere fluxes, biomass, streamflow and remotely sensed vegetation cover) and two state-of-the-art biospheric models, we show that climate variability and extremes lead to positive or negative responses in the biosphere, depending on vegetation type. We find Australia to be a global hot spot for variability, with semi-arid ecosystems in that country exhibiting increased carbon uptake due to both asymmetry in the interannual distribution of rainfall (extrinsic forcing), and asymmetry in the response of gross primary production (GPP) to rainfall change (intrinsic response). The latter is attributable to the pulse-response behaviour of the drought-adapted biota of these systems, a response that is estimated to be as much as half of that from the CO2 fertilization effect during 1990-2013. Mesic ecosystems, lacking drought-adapted species, did not show an intrinsic asymmetric response. Our findings suggest that a future more variable climate will induce large but contrasting ecosystem responses, differing among biomes globally, independent of changes in mean precipitation alone. The most significant changes are occurring in the extensive arid and semi-arid regions, and we suggest that the reported increased carbon uptake in response to asymmetric responses might be contributing to the observed greening trends there.

Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

AbstractThe Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate‐carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (δ18O) and carbon (δ13C) isotope records (5–12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic Ice Sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity, and X‐ray fluorescence (XRF) scanner‐derived carbonate records from IODP Sites U1335, U1336, U1337, and U1338 on a consistent, astronomically tuned timescale. Benthic isotope and XRF scanner‐derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on δ13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with >75% carbonate loss occurring at paleodepths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (δ18O minima) and δ13C decreases, implying that climate‐carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial‐interglacial pattern, where dissolution maxima correspond to δ13C maxima and δ18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

Process contributions of Australian ecosystems to interannual variations in the carbon cycle

New evidence is emerging that semi-arid ecosystems dominate interannual variability (IAV) of the global carbon cycle, largely via fluctuating water availability associated with El Niño/Southern Oscillation. Recent evidence from global terrestrial biosphere modelling and satellite-based inversion of atmospheric CO2 point to a large role of Australian ecosystems in global carbon cycle variability, including a large contribution from Australia to the record land sink of 2011. However the specific mechanisms governing this variability, and their bioclimatic distribution within Australia, have not been identified. Here we provide a regional assessment, based on best available observational data, of IAV in the Australian terrestrial carbon cycle and the role of Australia in the record land sink anomaly of 2011. We find that IAV in Australian net carbon uptake is dominated by semi-arid ecosystems in the east of the continent, whereas the 2011 anomaly was more uniformly spread across most of the continent. Further, and in contrast to global modelling results suggesting that IAV in Australian net carbon uptake is amplified by lags between production and decomposition, we find that, at continental scale, annual variations in production are dampened by annual variations in decomposition, with both fluxes responding positively to precipitation anomalies.

Seasonal trends of Amazonian rainforest phenology, net primary productivity, and carbon allocation

AbstractThe seasonality of solar irradiance and precipitation may regulate seasonal variations in tropical forests carbon cycling. Controversy remains over their importance as drivers of seasonal dynamics of net primary productivity in tropical forests. We use ground data from nine lowland Amazonian forest plots collected over 3 years to quantify the monthly primary productivity (NPP) of leaves, reproductive material, woody material, and fine roots over an annual cycle. We distinguish between forests that do not experience substantial seasonal moisture stress (“humid sites”) and forests that experience a stronger dry season (“dry sites”). We find that forests from both precipitation regimes maximize leaf NPP over the drier season, with a peak in production in August at both humid (mean 0.39 ± 0.03 Mg C ha−1 month−1 in July, n = 4) and dry sites (mean 0.49 ± 0.03 Mg C ha−1 month−1 in September, n = 8). We identify two distinct seasonal carbon allocation patterns (the allocation of NPP to a specific organ such as wood leaves or fine roots divided by total NPP). The forests monitored in the present study show evidence of either (i) constant allocation to roots and a seasonal trade‐off between leaf and woody material or (ii) constant allocation to wood and a seasonal trade‐off between roots and leaves. Finally, we find strong evidence of synchronized flowering at the end of the dry season in both precipitation regimes. Flower production reaches a maximum of 0.047 ± 0.013 and 0.031 ± 0.004 Mg C ha−1 month−1 in November, in humid and dry sites, respectively. Fruitfall production was staggered throughout the year, probably reflecting the high variation in varying times to development and loss of fruit among species.

Climate science: Hidden trends in the ocean carbon sink.

Simulations of the flux of atmospheric carbon dioxide into the ocean show that changes in flux associated with human activities are currently masked by natural climate variations, but will be evident in the near future. See Letter p.469 The world's oceans have taken up vast amounts of amount of carbon produced by fossil fuel burning during the industrial era. These authors use a large ensemble of a single Earth system climate model, the Community Earth System Model–Large Ensemble (CESM–LE), to assess variability and change in the ocean carbon cycle in recent decades and through to 2100. This approach allows for a separation between trends in the air–sea carbon flux due to anthropogenic climate change and those due to internal climate variability. The study reveals how the ocean carbon sink may be expected to change throughout this century in different oceanic regions. The findings suggest that a large internal climate variability makes it unlikely that changes in the rate of anthropogenic carbon uptake can be directly observed in most oceanic regions at present, but that this may become possible between 2020 and 2050 in some regions.

High-resolution SIMS oxygen isotope analysis on conodont apatite from South China and implications for the end-Permian mass extinction

Understanding the interplay of climatic and biological events in deep time requires resolving the precise timing and pattern of paleotemperature changes and their temporal relationship with carbon cycle variations and biodiversity fluctuations. In situ oxygen isotope analyses of conodont apatite from South China enables us to reconstruct high-resolution seawater temperature records across the Permian–Triassic boundary (PTB) intervals in the upper slope (Meishan), lower slope (Shangsi), and carbonate platform (Daijiagou and Liangfengya) settings. Constrained by the latest high-precision geochronological dates and high-resolution conodont biozones, we can establish the temporal and spatial patterns of seawater temperature changes and assess their potential connections with the carbon cycle disruption and biodiversity decline. We find a rapid warming of ~10°C during the latest Permian–earliest Triassic that postdated the onset of the negative shift in δ13Ccarb by ~81kyr (thousand years), the abrupt decline in δ13Ccarb by ~32kyr and the onset of mass extinction by ~23kyr, which contradicts previous claims that the extreme temperature rise started immediately before or coincided with the onset of mass extinction. Our new evidence indicates that climate warming was most likely not a direct cause for the main pulse of the end-Permian mass extinction (EPME), but rather a later participant or a catalyst that increased the pace of the biodiversity decline. In addition, a prominent cooling is recorded in the earliest Changhsingian, with the main phase (a drop of ~8°C in ~0.2Ma) confined to the lower part of the Clarkina wangi zone and synchronous with the positive limb of the carbon isotope excursion (CIE) around the Wuchiapingian–Changhsingian boundary (WCB) in Meishan and Shangsi. Further long-term and high-resolution studies from other sections are needed to confirm the full contexts and underlying dynamics of the WCB “cooling event”.

Variations in microbial carbon sources and cycling in the deep continental subsurface

Deep continental subsurface fracture water systems, ranging from 1.1 to 3.3km below land surface (kmbls), were investigated to characterize the indigenous microorganisms and elucidate microbial carbon sources and their cycling. Analysis of phospholipid fatty acid (PLFA) abundances and direct cell counts detected varying biomass that was not correlated with depth. Compound-specific carbon isotope analyses (δ13C and Δ14C) of the phospholipid fatty acids (PLFAs) and carbon substrates combined with genomic analyses did identify, however, distinct carbon sources and cycles between the two depth ranges studied.In the shallower boreholes at circa 1kmbls, isotopic evidence indicated microbial incorporation of biogenic CH4 by the in situ microbial community. At the shallowest site, 1.05kmbls in Driefontein mine, this process clearly dominated the isotopic signal. At slightly deeper depths, 1.34kmbls in Beatrix mine, the isotopic data indicated the incorporation of both biogenic CH4 and dissolved inorganic carbon (DIC) derived from CH4 oxidation. In both of these cases, molecular genetic analysis indicated that methanogenic and methanotrophic organisms together comprised a small component (<5%) of the microbial community. Thus, it appears that a relatively minor component of the prokaryotic community is supporting a much larger overall bacterial community in these samples.In the samples collected from >3kmbls in Tau Tona mine (TT107, TT109 Bh2), the CH4 had an isotopic signature suggesting a predominantly abiogenic origin with minor inputs from microbial methanogenesis. In these samples, the isotopic enrichments (δ13C and Δ14C) of the PLFAs relative to CH4 were consistent with little incorporation of CH4 into the biomass. The most 13C-enriched PLFAs were observed in TT107 where the dominant CO2-fixation pathway was the acetyl-CoA pathway by non-acetogenic bacteria. The differences in the δ13C of the PLFAs and the DIC and DOC for TT109 Bh2 were ∼−24‰ and 0‰, respectively. The dominant CO2-fixation pathways were 3-HP/4-HB cycle>acetyl-CoA pathway>reductive pentose phosphate cycle.

Role of Southern Ocean stratification in glacial atmospheric CO2 reduction evaluated by a three-dimensional ocean general circulation model

Atmospheric carbon dioxide (CO2) concentration during glacial periods is known to be considerably lower than during interglacial periods. However, previous studies using an ocean general circulation model (OGCM) fail to reproduce this. Paleoclimate proxy data of the Last Glacial Maximum indicate high salinity (>37.0 psu) and long water mass residence time (>3,000 years) in the Southern Ocean, suggesting that salinity stratification was enhanced and more carbon was stored there. Reproducibility of salinity and water mass age is considered insufficient in previous OGCMs, which might affect the reproducibility of atmospheric CO2 concentration. This study investigated the role of increased stratification of the Southern Ocean in the glacial CO2 variation using an OGCM. We found that deep water formation in East Antarctica is required to explain high salinity in the South Atlantic. Saltier deep Southern Ocean resulted in increased atmospheric CO2 concentration against previous estimates. This is partly due to increased volume transport of Antarctic Bottom Water and associated decrease in the water mass age of the deep Pacific Ocean. On the other hand, weakening of vertical mixing contributed to increase of the vertical gradient of dissolved inorganic carbon and decrease of atmospheric CO2 concentration. However, we show that it is unable to explain all of the glacial CO2 variations by the contribution of the Southern Ocean. Our findings indicate that detailed understanding of the impact of enhanced stratification in the Southern Ocean on the Pacific Ocean might be crucial to understanding the mechanisms behind the glacial-interglacial ocean carbon cycle variations.

Including an ocean carbon cycle model into &amp;lt;i&amp;gt;i&amp;lt;/i&amp;gt;LOVECLIM (v1.0)

Abstract. The atmospheric carbon dioxide concentration plays a crucial role in the radiative balance and as such has a strong influence on the evolution of climate. Because of the numerous interactions between climate and the carbon cycle, it is necessary to include a model of the carbon cycle within a climate model to understand and simulate past and future changes of the carbon cycle. In particular, natural variations of atmospheric CO2 have happened in the past, while anthropogenic carbon emissions are likely to continue in the future. To study changes of the carbon cycle and climate on timescales of a few hundred to a few thousand years, we have included a simple carbon cycle model into the iLOVECLIM Earth System Model. In this study, we describe the ocean and terrestrial biosphere carbon cycle models and their performance relative to observational data. We focus on the main carbon cycle variables including the carbon isotope ratios δ13C and the Δ14C. We show that the model results are in good agreement with modern observations both at the surface and in the deep ocean for the main variables, in particular phosphates, dissolved inorganic carbon and the carbon isotopes.

Early Paleogene variations in the calcite compensation depth: new constraints using old borehole sediments from across Ninetyeast Ridge, central Indian Ocean

Abstract. Major variations in global carbon cycling occurred between 62 and 48 Ma, and these very likely related to changes in the total carbon inventory of the ocean-atmosphere system. Based on carbon cycle theory, variations in the mass of the ocean carbon should be reflected in contemporaneous global ocean carbonate accumulation on the seafloor and, thereby, the depth of the calcite compensation depth (CCD). To better constrain the cause and magnitude of these changes, the community needs early Paleogene carbon isotope and carbonate accumulation records from widely separated deep-sea sediment sections, especially including the Indian Ocean. Several CCD reconstructions for this time interval have been generated using scientific drill sites in the Atlantic and Pacific oceans; however, corresponding information from the Indian Ocean has been extremely limited. To assess the depth of the CCD and the potential for renewed scientific drilling of Paleogene sequences in the Indian Ocean, we examine lithologic, nannofossil, carbon isotope, and carbonate content records for late Paleocene – early Eocene sediments recovered at three sites spanning Ninetyeast Ridge: Deep Sea Drilling Project (DSDP) Sites 213 (deep, east), 214 (shallow, central), and 215 (deep, west). The disturbed, discontinuous sediment sections are not ideal, because they were recovered in single holes using rotary coring methods, but remain the best Paleogene sediments available from the central Indian Ocean. The δ13C records at Sites 213 and 215 are similar to those generated at several locations in the Atlantic and Pacific, including the prominent high in δ13C across the Paleocene carbon isotope maximum (PCIM) at Site 215, and the prominent low in δ13C across the early Eocene Climatic Optimum (EECO) at both Site 213 and Site 215. The Paleocene-Eocene thermal maximum (PETM) and the K/X event are found at Site 213 but not at Site 215, presumably because of coring gaps. Carbonate content at both Sites 213 and 215 drops to &lt;5% shortly after the first occurrence of Discoaster lodoensis and the early Eocene rise in δ13C (~52 Ma). This reflects a rapid shoaling of the CCD, and likely a major decrease in the net flux of 13C-depleted carbon to the ocean. Our results support ideas that major changes in net fluxes of organic carbon to and from the exogenic carbon cycle occurred during the early Paleogene. Moreover, we conclude that excellent early Paleogene carbonate accumulation records might be recovered from the central Indian Ocean with future scientific drilling.

Understanding climate change: science, policy, and practice

1. Climate Change in the Public Sphere 1.1. Communicating about climate change 1.2. The state of the science 1.3. Responding to climate change: mitigation and adaptation 1.4. The state of the policy 1.4.1. The United Nations Framework Convention on Climate Change and the Kyoto Protocol 1.4.2. The United Nations Conference on Environment and Development (Rio, and Rio +20) 1.4.3. The Intergovernmental Panel on Climate Change 1.5. The scale of the challenge: accelerating action on climate change 1.6. Roadmap to the book 2. Basic System Dynamics 2.1. What's a system? 2.1.1. System parts and interactions 2.1.2. Stocks and flows 2.1.3. Feedbacks 2.1.4. Lags 2.1.5. Function or purpose 2.2. Earth's Climate System: The parts and interconnections 2.2.1. Atmosphere, Hydrosphere, Biosphere, Geosphere, and Anthroposphere 2.2.2. The Ins and Out of Earth's Energy Budget 3. Climate controls: Energy from the Sun 3.1. Incoming Solar Radiation 3.1.1. Blackbody radiation: the Sun versus Earth 3.1.2. Our place in space: the Goldilocks planet 3.2. Natural Variability 3.2.1. 4.5 billion years of solar energy 3.2.2. Orbital controls: baseline variability in the past million years 3.2.3. Sunspots: how big a deal? 3.3. Mitigation strategies and policy tools 4. Climate Controls: Earth's Reflectivity 4.1. Natural Variability 4.1.1. At Earth's surface: Ice, water, and vegetation 4.1.2. In the atmosphere: Aerosols and clouds 4.2. Anthropogenic Variability 4.2.1. Land-use changes 4.2.2. Anthropogenic Aerosols 4.3. Mitigation strategies and policy tools 5. Climate Controls: The Greenhouse effect 5.1. How does the greenhouse effect work? 5.1.1. Characteristics of a good greenhouse gas 5.1.2. Energy flows in a greenhouse world 5.2. The unperturbed carbon cycle and natural greenhouse variability 5.2.1. Carbon stocks and flows 5.2.2. Timescales of natural greenhouse variability 5.2.3. Feedbacks involving the greenhouse effect 5.3. Anthropogenic interference 5.3.1. Perturbed stocks, flows, and chemical fingerprints 5.3.2. Cumulative carbon emissions: a budget 6. The Core of Climate Change Mitigation: Reducing Greenhouse Gas Emissions and Transforming the Energy System 6.1. Introduction to reducing greenhouse gas emissions 6.2. The Global Energy System 6.3. Mitigation Strategies 6.3.1. Demand-side mitigation: energy efficiency and conservation 6.3.2. Supply-side mitigation 6.3.3. Carbon capture and storage 6.4. Fostering accelerated and transformative mitigation 7. Climate Models 7.1. Climate Model Basics 7.1.1. Physical Principles 7.1.2. The Role of Observations 7.1.3. Time and Space 7.1.4. Parameterization 7.1.5. Testing climate models 7.2. Types of climate models 7.2.1. Energy Balance Models 7.2.2. Earth System Models of Intermediate Complexity 7.2.3. General Circulation Models 7.2.4. Regional Climate Models 7.2.5. Integrated Assessment Models 7.3. Certainties and Uncertainties 8. Future Climate: Emissions, climate, and what we do about it 8.1. Emissions scenarios SRES scenario 'families' and storylines 8.1.1. Post-SRES and Representative Concentration Pathways 8.1.2. 8.2. Global Climate in 2100 Temperature, precipitation, sea level rise, and extreme events 8.2.1. Uncertainty 8.2.2. 8.3. Regional forecasting 8.4. Backcasting 8.5. Scale of the challenge: Transforming emissions pathways 9. Climate Change Impacts on Natural Systems 9.1. Observed Impacts Impacts on Land 9.1.1. Impacts in the Oceans 9.1.2. 9.2. Adaptation in Natural Systems 9.3. Policy Tools and Progress International tools 9.3.1. National and sub-national tools 9.3.2. 9.4. Conclusions 10. Climate Change Impacts on Human Systems 10.1. Introduction 10.2. Key concepts in climate change impacts and adaptation 10.3. Observed and Projected Impacts 10.3.1. Climate change impacts on food and water 10.3.2. Climate change impacts on cities and infrastructure 10.3.3. Equity implications: Health, culture, and global distribution of wealth 10.4. Adaptation in human systems 10.5. Policy Tools and Progress 10.5.1. Policy tools for adaptation 10.5.2. International and national adaptation 10.5.3. Sub-national adaptation 10.5.4. Social movements and human behavior change: the root of the adaptation conundrum 11. The Frontier: Innovative Action on Climate Change 11.1. Integrating Adaptation and Mitigation: Pursuing Sustainability 11.2. What Road will we choose? The ethics of geoengineering 11.3. Transformative change: reorienting development paths to yield a sustainable future 11.4. Conclusions and future directions

The New Phytologist Tansley Medal 2014.

Each year, the New Phytologist Trust awards the Tansley Medal to scientists that have made an outstanding contribution to plant science within five years of receiving their PhD. Since its foundation in 2009, the Tansley Medal has been awarded to researchers with broad research interests that encompass the whole breadth of plant science (Woodward & Hetherington, 2010, 2011; Dolan, 2012, 2013, 2014). We are delighted to award the 2014 Tansley Medal to William Anderegg of Princeton University, NJ, USA (Box 1). William's PhD entitled ‘Physiological pathways and consequences of widespread, climate-induced forest die-off’ was conducted with Christopher Field at Stanford University and he is currently a National Oceanic and Atmospheric Administration Climate and Global Change Post-doctoral Research Fellow at Princeton University. William did his PhD with Dr Christopher Field in the Department of Biology at Stanford University and the Department of Global Ecology at the Carnegie Institution for Science, Washington, DC, USA. His research examined the consequences and physiological mechanisms of widespread, drought-induced forest die-off, using Populus tremuloides in the western United States as a model system. His research illuminated the hydraulic underpinnings of plant death, discovered hydraulic deterioration, where accumulated damage to the plant hydraulic system leads to death multiple years after the inciting drought stress, and culminated in a predictive model of tree mortality. As a post-doctoral fellow, William is examining the legacy effects of drought and drought recovery, evolutionary trade-offs in plant hydraulics, and carbon cycle variability at the regional and global scale. For more information on William, visit http://wrlanderegg.com or contact William at [email protected]. William will receive a £2000 prize in association with the Tansley Medal award http://www.newphytologist.org/tansleymedal.htm William's Minireview entitled ‘Spatial and temporal variation in plant hydraulic traits and their relevance for climate change impacts on vegetation’ is published in this issue of New Phytologist (Anderegg, pp. 1008–1014), and explores the variability of cavitation resistance in the context of climate change. The calibre of shortlisted candidates for the 2014 competition was exceptionally high and this is reflected in the minireviews published in this issue of New Phytologist: Well done to this year's finalists on their achievements. All at New Phytologist offer our warmest congratulations and we wish them well in their future careers.

High-precision dual-inlet IRMS measurements of the stable isotopes of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and the N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O / CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; ratio from polar ice core samples

Abstract. An important constraint on mechanisms of past carbon cycle variability is provided by the stable isotopic composition of carbon in atmospheric carbon dioxide (δ13C-CO2) trapped in polar ice cores, but obtaining very precise measurements has proven to be a significant analytical challenge. Here we describe a new technique to determine the δ13C of CO2 at very high precision, as well as measuring the CO2 and N2O mixing ratios. In this method, ancient air is extracted from relatively large ice samples (~400 g) with a dry-extraction "ice grater" device. The liberated air is cryogenically purified to a CO2 and N2O mixture and analyzed with a microvolume-equipped dual-inlet IRMS (Thermo MAT 253). The reproducibility of the method, based on replicate analysis of ice core samples, is 0.02‰ for δ13C-CO2 and 2 ppm and 4 ppb for the CO2 and N2O mixing ratios, respectively (1σ pooled standard deviation). Our experiments show that minimizing water vapor pressure in the extraction vessel by housing the grating apparatus in a ultralow-temperature freezer (−60 °C) improves the precision and decreases the experimental blank of the method to −0.07 ± 0.04‰. We describe techniques for accurate calibration of small samples and the application of a mass-spectrometric method based on source fragmentation for reconstructing the N2O history of the atmosphere. The oxygen isotopic composition of CO2 is also investigated, confirming previous observations of oxygen exchange between gaseous CO2 and solid H2O within the ice archive. These data offer a possible constraint on oxygen isotopic fractionation during H2O and CO2 exchange below the H2O bulk melting temperature.

Terrestrial evidence for a two-stage mid-Paleocene biotic event

Marine records of the Paleocene indicate a series of hyperthermal events characterized by significant climatic and carbon cycle variability, but there are few comparable continental records. The mid-Paleocene biotic event (MPBE) is a recently described interval defined by a rapid negative carbon isotope excursion and major short-term changes in marine ecosystems, but it is as yet unclear whether the event was globally important. Here we present the first terrestrial paleoenvironmental record of the MPBE based on paleosols that document rapid and short-lived increases in temperature and precipitation and resultant shifts in plant assemblages concomitant with substantial carbon isotope excursions. The new record indicates that carbon cycle changes during the early late Paleocene may have resulted in a two-stage transient hyperthermal event that caused a significant perturbation to both the regional climate and terrestrial ecology of South America in addition to the major biotic event (MPBE) previously recognized in marine records. Overall, this suggests that the MPBE may have been a global climate event with far-reaching environmental impacts in both the marine and terrestrial realms.

Large Differences in Terrestrial Vegetation Production Derived from Satellite-Based Light Use Efficiency Models

Terrestrial gross primary production (GPP) is the largest global CO2 flux and determines other ecosystem carbon cycle variables. Light use efficiency (LUE) models may have the most potential to adequately address the spatial and temporal dynamics of GPP, but recent studies have shown large model differences in GPP simulations. In this study, we investigated the GPP differences in the spatial and temporal patterns derived from seven widely used LUE models at the global scale. The result shows that the global annual GPP estimates over the period 2000–2010 varied from 95.10 to 139.71 Pg C∙yr−1 among models. The spatial and temporal variation of global GPP differs substantially between models, due to different model structures and dominant environmental drivers. In almost all models, water availability dominates the interannual variability of GPP over large vegetated areas. Solar radiation and air temperature are not the primary controlling factors for interannual variability of global GPP estimates for most models. The disagreement among the current LUE models highlights the need for further model improvement to quantify the global carbon cycle.