Differences in reported life span of mice heterozygous for a null allele of the insulin receptor substrate-2 (Irs2) might involve the effects of diet, breeding strategies, and genetic background on insulin-like signaling cascades. A better understanding will emerge from studies focusing on the coordination of nutrient homeostasis and life span by insulin-like signaling in specific peripheral tissues and the central nervous system.

Summary (149 words of referenced text): 46The climate impact of aerosols is highly uncertain owing primarily to their poorly quantified 47 influence on cloud properties. During 2014-15, a fissure eruption in Holuhraun (Iceland) 48 emitted huge quantities of sulphur dioxide, resulting in significant reductions in liquid cloud 49 droplet size. Using satellite observations and detailed modelling, we estimate a global mean 50 radiative forcing from the resulting aerosol-induced cloud brightening for the time of the 51 eruption of around -0.2 W.m -2 . Changes in cloud amount or liquid water path are 52 undetectable, indicating that these aerosol-cloud indirect effects are modest. It supports the 53 idea that cloud systems are well buffered against aerosol changes as only impacts on cloud 54 effective radius appear relevant from a climate perspective, thus providing a strong constraint 55 on aerosol-cloud interactions. This result will reduce uncertainties in future climate 56 projections as we are able to reject the results from climate models with an excessive liquid 57 water path response. 58 59Main Text: (3103 words of referenced text, including concluding paragraph) 60 The 2014-15 eruption at Holuhraun (486 words of referenced text): 61Anthropogenic emissions that affect climate are not just confined to greenhouse gases. 62Sulphur dioxide and other pollutants form atmospheric aerosols that can scatter and absorb 63 sunlight and can influence the properties of clouds, modulating the Earth-atmosphere energy 64 balance. Aerosols act as cloud condensation nuclei (CCN); an increase in CCN translates into 65 a higher number of smaller, more reflective cloud droplets that scatter more sunlight back to 66 space 1 (the ÔfirstÕ indirect effect of aerosols). Smaller cloud droplets decrease the efficiency 67 of collision-coalescence processes that are pivotal in rain initiation, thus aerosol-influenced 68 clouds may retain more liquid water and extend coverage/lifetime 2,3 (the ÔsecondÕ or Ôcloud 69 lifetimeÕ indirect effect). Aerosols usually co-vary with key environmental variables making 70 it difficult to disentangle aerosol-cloud impacts from meteorological variability [4][5][6] . 71Additionally, clouds themselves are complex transient systems subject to dynamical 72 feedbacks (e.g. cloud top entrainment/evaporation, invigoration of convection) which 73 influence cloud response [7][8][9][10][11][12] . These aspects present great challenges in evaluating and 74 constraining aerosol-cloud interactions (ACI) in General Circulation Models (GCM) 13-17 , 75 with particular contentious debate surrounding the relative importance of these feedback 76 mechanisms. 77Nonetheless, anthropogenic aerosol emissions are thought to cool the Earth via indirect 78 effects 17 , but the uncertainty ranges from -1.2 to -0.0 W.m -2 (90% confidence interval) due to 79 i) a lack of characterization of the pre-industrial aerosol state 15,18,19 , and ii) model parametric 80 and structural errors in representing cloud responses to aerosol chan...

[1] Absorbing aerosols such as smoke strongly absorb solar radiation, particularly at ultraviolet and visible/near-infrared (VIS/NIR) wavelengths, and their presence above clouds can have considerable implications. It has been previously shown that they have a positive (i.e., warming) direct aerosol radiative effect (DARE) when overlying bright clouds. Additionally, they can cause biased passive instrument satellite retrievals in techniques that rely on VIS/NIR wavelengths for inferring the cloud optical thickness (COT) and effective radius (r e ) of underlying clouds, which can in turn yield biased above-cloud DARE estimates. Here we investigate Moderate Resolution Imaging Spectroradiometer (MODIS) cloud optical property retrieval biases due to overlying absorbing aerosols observed by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and examine the impact of these biases on above-cloud DARE estimates. The investigation focuses on a region in the southeast Atlantic Ocean during August and September (2006-2011), where smoke from biomass burning in southern Africa overlies persistent marine boundary layer stratocumulus clouds. Adjusting for above-cloud aerosol attenuation yields increases in the regional mean liquid COT (averaged over all ocean-only liquid clouds) by roughly 6%; mean r e increases by roughly 2.6%, almost exclusively due to the COT adjustment in the non-orthogonal retrieval space. It is found that these two biases lead to an underestimate of DARE. For liquid cloud Aqua MODIS pixels with CALIOP-observed above-cloud smoke, the regional mean above-cloud radiative forcing efficiency (DARE per unit aerosol optical depth (AOD)) at time of observation (near local noon for Aqua overpass) increases from 50.9WmÀ2 AOD À1 to 65.1Wm À2 AOD À1 when using bias-adjusted instead of nonadjusted MODIS cloud retrievals.Citation: Meyer, K., S. Platnick, L. Oreopoulos, and D. Lee (2013), Estimating the direct radiative effect of absorbing aerosols overlying marine boundary layer clouds in the southeast Atlantic using MODIS and CALIOP,

An international Intercomparison of 3D Radiation Codes (I3RC) underscores the vast progress of recent years, but also highlights the challenges ahead for routine implementation in remote sensing and global climate modeling applications. Modeling atmospheric and oceanic processes is one of the most important methods of the earth sciences for understanding the interactions of the various components of the surface-atmosphere system and predicting future weather and climate states. Great leaps in the availability of computing power at continuously decreasing costs have led to widespread popularity of computer models for research and operational applications. As part of routine scientific work, output from models built for AFFILIATIONS: CAHALAN-NASA

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

.[1] We present results from Phase I of the Continual Intercomparison of Radiation Codes (CIRC), intended as an evolving and regularly updated reference source for evaluation of radiative transfer (RT) codes used in global climate models and other atmospheric applications. CIRC differs from previous intercomparisons in that it relies on an observationally validated catalog of cases. The seven CIRC Phase I baseline cases, five cloud free and two with overcast liquid clouds, are built around observations by the Atmospheric Radiation Measurements program that satisfy the goals of Phase I, namely, to examine RT model performance in realistic, yet not overly complex, atmospheric conditions. Besides the seven baseline cases, additional idealized "subcases" are also employed to facilitate interpretation of model errors. In addition to quantifying individual model performance with respect to reference line-by-line calculations, we also highlight RT code behavior for conditions of doubled CO 2 , issues arising from spectral specification of surface albedo, and the impact of cloud scattering in the thermal infrared. Our analysis suggests that improvements in the calculation of diffuse shortwave flux, shortwave absorption, and shortwave CO 2 forcing as well as in the treatment of spectral surface albedo should be considered for many RT codes. On the other hand, longwave calculations are generally in agreement with the reference results. By expanding the range of conditions under which participating codes are tested, future CIRC phases will hopefully allow even more rigorous examination of RT codes.

Abstract. In this study we examine the performance of 31 global model radiative transfer schemes in cloud-free conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scattering-only aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multi-angular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly −10 to 20%, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

We update previously published MODIS global cloud regimes (CRs) using the latest MODIS cloud retrievals in the Collection 6 dataset. We implement a slightly different derivation method, investigate the composition of the regimes, and then proceed to examine several aspects of CR radiative appearance with the aid of various radiative flux datasets. Our results clearly show the CRs are radiatively distinct in terms of shortwave, longwave and their combined (total) cloud radiative effect. We show that we can clearly distinguish regimes based on whether they radiatively cool or warm the atmosphere, and thanks to radiative heating profiles to discern the vertical distribution of cooling and warming. Terra and Aqua comparisons provide information about the degree to which morning and afternoon occurrences of regimes affect the symmetry of CR radiative contribution. We examine how the radiative discrepancies among multiple irradiance datasets suffering from imperfect spatiotemporal matching depend on CR, and whether they are therefore related to the complexity of cloud structure, its interpretation by different observational systems, and its subsequent representation in radiative transfer calculations.