Twenty-first-century compatible co2 emissions and airborne fraction simulated by cmip5 earth system models under four representative concentration pathways

PublishedJournal ArticleThe carbon cycle is a crucial Earth system component affecting climate and atmospheric composition. The response of natural carbon uptake to CO2 and climate change will determine anthropogenic emissions compatible with a target CO2 pathway. For phase 5 of the Coupled Model Intercomparison Project (CMIP5), four future representative concentration pathways (RCPs) have been generated by integrated assessment models (IAMs) and used as scenarios by state-of-the-art climate models, enabling quantification of compatible carbon emissions for the four scenarios by complex, process-based models. Here, the authors present results from 15 such Earth system GCMs for future changes in land and ocean carbon storage and the implications for anthropogenic emissions. The results are consistent with the underlying scenarios but show substantial model spread. Uncertainty in land carbon uptake due to differences among models is comparable with the spread across scenarios. Model estimates of historical fossil-fuel emissions agree well with reconstructions, and future projections for representative concentration pathway 2.6 (RCP2.6) and RCP4.5 are consistent with the IAMs. For high-end scenarios (RCP6.0 and RCP8.5), GCMs simulate smaller compatible emissions than the IAMs, indicating a larger climate-carbon cycle feedback in the GCMs in these scenarios. For the RCP2.6 mitigation scenario, an average reduction of 50% in emissions by 2050 from 1990 levels is required but with very large model spread (14%-96%). The models also disagree on both the requirement for sustained negative emissions to achieve the RCP2.6 CO2 concentration and the success of this scenario to restrict global warming below 28C. All models agree that the future airborne fraction depends strongly on the emissions profile with higher airborne fraction for higher emissions scenarios. ©2013 American Meteorological Society.MOHC authors were supported by the JointDECC/Defra MetOffice Hadley Centre Climate Programme (GA01101), and work to performHadGEM2- ES and MPI-ESM CMIP5 simulations was supported by the EU-FP7 COMBINE project (Grant 226520). JS was supported by the EU-FP7 CARBOCHANGE project (Grant 284679). We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. For CMIP, the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. JT and CR were supported by the Research Council of Norway through the EarthClim (207711/E10) project

Differential Regulation of the Period Genes in Striatal Regions following Cocaine Exposure

Several studies have suggested that disruptions in circadian rhythms contribute to the pathophysiology of multiple psychiatric diseases, including drug addiction. In fact, a number of the genes involved in the regulation of circadian rhythms are also involved in modulating the reward value for drugs of abuse, like cocaine. Thus, we wanted to determine the effects of chronic cocaine on the expression of several circadian genes in the Nucleus Accumbens (NAc) and Caudate Putamen (CP), regions of the brain known to be involved in the behavioral responses to drugs of abuse. Moreover, we wanted to explore the mechanism by which these genes are regulated following cocaine exposure. Here we find that after repeated cocaine exposure, expression of the Period (Per) genes and Neuronal PAS Domain Protein 2 (Npas2) are elevated, in a somewhat regionally selective fashion. Moreover, NPAS2 (but not CLOCK (Circadian Locomotor Output Cycles Kaput)) protein binding at Per gene promoters was enhanced following cocaine treatment. Mice lacking a functional Npas2 gene failed to exhibit any induction of Per gene expression after cocaine, suggesting that NPAS2 is necessary for this cocaine-induced regulation. Examination of Per gene and Npas2 expression over twenty-four hours identified changes in diurnal rhythmicity of these genes following chronic cocaine, which were regionally specific. Taken together, these studies point to selective disruptions in Per gene rhythmicity in striatial regions following chronic cocaine treatment, which are mediated primarily by NPAS2. © 2013 Falcon et al

Robust Food Anticipatory Activity in BMAL1-Deficient Mice

Food availability is a potent environmental cue that directs circadian locomotor activity in rodents. Even though nocturnal rodents prefer to forage at night, daytime food anticipatory activity (FAA) is observed prior to short meals presented at a scheduled time of day. Under this restricted feeding regimen, rodents exhibit two distinct bouts of activity, a nocturnal activity rhythm that is entrained to the light-dark cycle and controlled by the master clock in the suprachiasmatic nuclei (SCN) and a daytime bout of activity that is phase-locked to mealtime. FAA also occurs during food deprivation, suggesting that a food-entrainable oscillator (FEO) keeps time in the absence of scheduled feeding. Previous studies have demonstrated that the FEO is anatomically distinct from the SCN and that FAA is observed in mice lacking some circadian genes essential for timekeeping in the SCN. In the current study, we optimized the conditions for examining FAA during restricted feeding and food deprivation in mice lacking functional BMAL1, which is critical for circadian rhythm generation in the SCN. We found that BMAL1-deficient mice displayed FAA during restricted feeding in 12hr light:12hr dark (12L:12D) and 18L:6D lighting cycles, but distinct activity during food deprivation was observed only in 18L:6D. While BMAL1-deficient mice also exhibited robust FAA during restricted feeding in constant darkness, mice were hyperactive during food deprivation so it was not clear that FAA consistently occurred at the time of previously scheduled food availability. Taken together, our findings suggest that optimization of experimental conditions such as photoperiod may be necessary to visualize FAA in genetically modified mice. Furthermore, the expression of FAA may be possible without a circadian oscillator that depends on BMAL1

Reconciling global-model estimates and country reporting of anthropogenic forest CO2 sinks

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordData availability: The data that support the findings of this study are available from the corresponding author upon request.Achieving the long-term temperature goal of the Paris Agreement requires forest-based mitigation. Collective progress towards this goal will be assessed by the Paris Agreement’s Global stocktake. At present, there is a discrepancy of about 4 GtCO2yr−1in global anthropogenic net land-use emissions between global models (reflected in IPCC assessment reports) and aggregated national GHG inventories (under the UNFCCC). We show that a substantial part of this discrepancy (about 3.2 GtCO2yr−1) can be explained by conceptual differences in anthropogenic forest sink estimation, related to the representation of environmental change impacts and the areas considered as managed. For a more credible tracking of collective progress under the Global stocktake, these conceptual differences between models and inventories need to be reconciled. We implement a new method of disaggregation of global land model results that allows greater comparability with GHG inventories. This provides a deeper understanding of model–inventory differences, allowing more transparent analysis of forest-based mitigation and facilitating a more accurate Global stocktake.J.H. was supported by EU FP7 through project LUC4C (GA603542) and the UK NERC project GGRiLS-GAP. G.G. was supported by Administrative Arrangement Number 340203/2016/742550/SER/CLIMA.A3. A.K.J. was supported by the NSF (AGS 12-43071) and DOE (DE-SC0016323). J.E.M.S.N. was supported by the German Research Foundation’s Emmy Noether Programme (grant number PO1751/1-1). G.G., J.H., G.P.P. and L.P. received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 776810 (VERIFY). C.D.K. was supported by the US DOE under Contract DE-AC02-05CH11231 as part of their RGMA (BGC-Feedbacks SFA) and TES Programs (NGEE-Tropics). A.K.J. was supported under the US NSF (NSF-AGS-12-43071)

Circadian Modulation of Gene Expression, but not Glutamate Uptake, in Mouse and Rat Cortical Astrocytes

Circadian clocks control daily rhythms including sleep-wake, hormone secretion, and metabolism. These clocks are based on intracellular transcription-translation feedback loops that sustain daily oscillations of gene expression in many cell types. Mammalian astrocytes display circadian rhythms in the expression of the clock genes Period1 (Per1) and Period2 (Per2). However, a functional role for circadian oscillations in astrocytes is unknown. Because uptake of extrasynaptic glutamate depends on the presence of Per2 in astrocytes, we asked whether glutamate uptake by glia is circadian.We measured glutamate uptake, transcript and protein levels of the astrocyte-specific glutamate transporter, Glast, and the expression of Per1 and Per2 from cultured cortical astrocytes and from explants of somatosensory cortex. We found that glutamate uptake and Glast mRNA and protein expression were significantly reduced in Clock/Clock, Per2- or NPAS2-deficient glia. Uptake was augmented when the medium was supplemented with dibutyryl-cAMP or B27. Critically, glutamate uptake was not circadian in cortical astrocytes cultured from rats or mice or in cortical slices from mice.We conclude that glutamate uptake levels are modulated by CLOCK, PER2, NPAS2, and the composition of the culture medium, and that uptake does not show circadian variations

Response operators for Markov processes in a finite state space: radius of convergence and link to the response theory for Axiom A systems

Using straightforward linear algebra we derive response operators describing the impact of small perturbations to finite state Markov processes. The results can be used for studying empirically constructed—e.g. from observations or through coarse graining of model simulations—finite state approximation of statistical mechanical systems. Recent results concerning the convergence of the statistical properties of finite state Markov approximation of the full asymptotic dynamics on the SRB measure in the limit of finer and finer partitions of the phase space are suggestive of some degree of robustness of the obtained results in the case of Axiom A system. Our findings give closed formulas for the linear and nonlinear response theory at all orders of perturbation and provide matrix expressions that can be directly implemented in any coding language, plus providing bounds on the radius of convergence of the perturbative theory. In particular, we relate the convergence of the response theory to the rate of mixing of the unperturbed system. One can use the formulas derived for finite state Markov processes to recover previous findings obtained on the response of continuous time Axiom A dynamical systems to perturbations, by considering the generator of time evolution for the measure and for the observables. A very basic, low-tech, and computationally cheap analysis of the response of the Lorenz ’63 model to perturbations provides rather encouraging results regarding the possibility of using the approximate representation given by finite state Markov processes to compute the system’s response

Resonances in a chaotic attractor crisis of the Lorenz Flow

Local bifurcations of stationary points and limit cycles have successfully been characterized in terms of the critical exponents of these solutions. Lyapunov exponents and their associated covariant Lyapunov vectors have been proposed as tools for supporting the understanding of critical transitions in chaotic dynamical systems. However, it is in general not clear how the statistical properties of dynamical systems change across a boundary crisis during which a chaotic attractor collides with a saddle. This behavior is investigated here for a boundary crisis in the Lorenz flow, for which neither the Lyapunov exponents nor the covariant Lyapunov vectors provide a criterion for the crisis. Instead, the convergence of the time evolution of probability densities to the invariant measure, governed by the semigroup of transfer operators, is expected to slow down at the approach of the crisis. Such convergence is described by the eigenvalues of the generator of this semigroup, which can be divided into two families, referred to as the stable and unstable Ruelle--Pollicott resonances, respectively. The former describes the convergence of densities to the attractor (or escape from a repeller) and is estimated from many short time series sampling the state space. The latter is responsible for the decay of correlations, or mixing, and can be estimated from a long times series, invoking ergodicity. It is found numerically for the Lorenz flow that the stable resonances do approach the imaginary axis during the crisis, as is indicative of the loss of global stability of the attractor. On the other hand, the unstable resonances, and a fortiori the decay of correlations, do not flag the proximity of the crisis, thus questioning the usual design of early warning indicators of boundary crises of chaotic attractors and the applicability of response theory close to such crises

Flow microenvironment of two marine peritrich ciliates with ectobiotic chemoautotrophic bacteria

The flow microenvironment of 2 marine peritrich ciliates, Vorticella sp. and Zoothamnium niveum, with ectobiotic sulfur bacteria was studied with frame-by-frame analyses of video sequences and a microsensor for fluid velocity. Both species populate the chemocline above H2Sreleasing mangrove peat. Vorticella sp. moves the surrounding seawater up to a horizontal and vertical distance of at least 400 μm with a maximum flow velocity of 18 mm s–1 close to its peristomial edge. The feather-shaped colonies of Z. niveum generate a unidirectional flow of seawater passing the colony perpendicular to the stalk; the convex side of the feather faces upstream. The flow velocity increased exponentially towards the colony, up to 11 mm s–1 at a distance of 100 μm. Contraction of the stalk forces the zooids of Vorticella sp. and Z. niveum towards the substrate at a high velocity of 71 and 520 mm s–1, respectively. During contraction of Vorticella sp., only little seawater is dragged along towards the surface to which the ciliates are attached whereas the contraction of Z. niveum resulted in a clear increase in the velocity of the seawater both surrounding the colony and above the substrate. Extension of the species proceeds 700 to 1000 times more slowly than contraction, and the surrounding seawater sticks to the cells and therefore is dragged along. The measurements given here support our earlier data indicating the importance of the feeding current for the bacteria-ciliate association, i.e. the cilia beat drives H2S- and O2-containing seawater toward the zooid at high velocity and thus, supports the growth of the ectobiotic sulfide-oxidizing bacteria. Rapid movement, shrinkage (Vorticella sp.) and bunching (Z. niveum) of the zooids during stalk contraction apparently cause sufficient shear stress to abrade ectobiotic bacteria that, once suspended, could enter the feeding currents

Will the tropical land biosphere dominate the climate-carbon cycle feedback during the twenty-first century?

Global warming caused by anthropogenic CO2 emissions is expected to reduce the capability of the ocean and the land biosphere to take up carbon. This will enlarge the fraction of the CO2 emissions remaining in the atmosphere, which in turn will reinforce future climate change. Recent model studies agree in the existence of such a positive climate-carbon cycle feedback, but the estimates of its amplitude differ by an order of magnitude, which considerably increases the uncertainty in future climate projections. Therefore we discuss, in how far a particular process or component of the carbon cycle can be identified, that potentially contributes most to the positive feedback. The discussion is based on simulations with a carbon cycle model, which is embedded in the atmosphere/ocean general circulation model ECHAM5/MPI-OM. Two simulations covering the period 1860-2100 are conducted to determine the impact of global warming on the carbon cycle. Forced by historical and future carbon dioxide emissions (following the scenario A2 of the Intergovernmental Panel on Climate Change), they reveal a noticeable positive climate-carbon cycle feedback, which is mainly driven by the tropical land biosphere. The oceans contribute much less to the positive feedback and the temperate/boreal terrestrial biosphere induces a minor negative feedback. The contrasting behavior of the tropical and temperate/boreal land biosphere is mostly attributed to opposite trends in their net primary productivity (NPP) under global warming conditions. As these findings depend on the model employed they are compared with results derived from other climate-carbon cycle models, which participated in the Coupled Climate-Carbon Cycle Model Intercomparison Project (C4MIP)