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  1. Abstract

    The Getz region of West Antarctica is losing ice at an increasing rate; however, the forcing mechanisms remain unclear. Here we use satellite observations and an ice sheet model to measure the change in ice speed and mass balance of the drainage basin over the last 25-years. Our results show a mean increase in speed of 23.8 % between 1994 and 2018, with three glaciers accelerating by over 44 %. Speedup across the Getz basin is linear, with speedup and thinning directly correlated confirming the presence of dynamic imbalance. Since 1994, 315 Gt of ice has been lost contributing 0.9 ± 0.6 mm global mean sea level, with increased loss since 2010 caused by a snowfall reduction. Overall, dynamic imbalance accounts for two thirds of the mass loss from this region of West Antarctica over the past 25-years, with a longer-term response to ocean forcing the likely driving mechanism.

     
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  2. Abstract. The Earth climate system is out of energy balance, and heat hasaccumulated continuously over the past decades, warming the ocean, the land,the cryosphere, and the atmosphere. According to the Sixth Assessment Reportby Working Group I of the Intergovernmental Panel on Climate Change,this planetary warming over multiple decades is human-driven and results inunprecedented and committed changes to the Earth system, with adverseimpacts for ecosystems and human systems. The Earth heat inventory providesa measure of the Earth energy imbalance (EEI) and allows for quantifyinghow much heat has accumulated in the Earth system, as well as where the heat isstored. Here we show that the Earth system has continued to accumulateheat, with 381±61 ZJ accumulated from 1971 to 2020. This is equivalent to aheating rate (i.e., the EEI) of 0.48±0.1 W m−2. The majority,about 89 %, of this heat is stored in the ocean, followed by about 6 %on land, 1 % in the atmosphere, and about 4 % available for meltingthe cryosphere. Over the most recent period (2006–2020), the EEI amounts to0.76±0.2 W m−2. The Earth energy imbalance is the mostfundamental global climate indicator that the scientific community and thepublic can use as the measure of how well the world is doing in the task ofbringing anthropogenic climate change under control. Moreover, thisindicator is highly complementary to other established ones like global meansurface temperature as it represents a robust measure of the rate of climatechange and its future commitment. We call for an implementation of theEarth energy imbalance into the Paris Agreement's Global Stocktake based onbest available science. The Earth heat inventory in this study, updated fromvon Schuckmann et al. (2020), is underpinned by worldwide multidisciplinarycollaboration and demonstrates the critical importance of concertedinternational efforts for climate change monitoring and community-basedrecommendations and we also call for urgently needed actions for enablingcontinuity, archiving, rescuing, and calibrating efforts to assure improvedand long-term monitoring capacity of the global climate observing system. The data for the Earth heat inventory are publicly available, and more details are provided in Table 4. 
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  3. Abstract. In sea-ice-covered areas, the sea ice floe size distribution (FSD) plays an important role in many processes affecting the coupled sea–ice–ocean–atmosphere system. Observations of the FSD are sparse – traditionally taken via a painstaking analysis of ice surface photography – and the seasonal and inter-annual evolution of floe size regionally and globally is largely unknown. Frequently, measured FSDs are assessed using a single number, the scaling exponent of the closest power-law fit to the observed floe size data, although in the absence of adequate datasets there have been limited tests of this “power-law hypothesis”. Here we derive and explain a mathematical technique for deriving statistics of the sea ice FSD from polar-orbiting altimeters, satellites with sub-daily return times to polar regions with high along-track resolutions. Applied to the CryoSat-2 radar altimetric record, covering the period from 2010 to 2018, and incorporating 11 million individual floe samples, we produce the first pan-Arctic climatology and seasonal cycle of sea ice floe size statistics. We then perform the first pan-Arctic test of the power-law hypothesis, finding limited support in the range of floe sizes typically analyzed in photographic observational studies. We compare the seasonal variability in observed floe size to fully coupled climate model simulations including a prognostic floe size and thickness distribution and coupled wave model, finding good agreement in regions where modeled ocean surface waves cause sea ice fracture. 
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  4. Abstract. Projection of the contribution of ice sheets to sea level change as part ofthe Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the formof simulations from coupled ice sheet–climate models and stand-alone icesheet models, overseen by the Ice Sheet Model Intercomparison Project forCMIP6 (ISMIP6). This paper describes the experimental setup forprocess-based sea level change projections to be performed with stand-aloneGreenland and Antarctic ice sheet models in the context of ISMIP6. TheISMIP6 protocol relies on a suite of polar atmospheric and oceanicCMIP-based forcing for ice sheet models, in order to explore the uncertaintyin projected sea level change due to future emissions scenarios, CMIPmodels, ice sheet models, and parameterizations for ice–ocean interactions.We describe here the approach taken for defining the suite of ISMIP6stand-alone ice sheet simulations, document the experimental framework andimplementation, and present an overview of the ISMIP6 forcing to beused by participating ice sheet modeling groups. 
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  5. null (Ed.)
    Abstract. Human-induced atmospheric composition changes cause a radiative imbalance atthe top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain ofthe Earth system – and particularly how much and where the heat isdistributed – is fundamental to understanding how this affects warmingocean, atmosphere and land; rising surface temperature; sea level; and lossof grounded and floating ice, which are fundamental concerns for society.This study is a Global Climate Observing System (GCOS) concertedinternational effort to update the Earth heat inventory and presents anupdated assessment of ocean warming estimates as well as new and updated estimatesof heat gain in the atmosphere, cryosphere and land over the period1960–2018. The study obtains a consistent long-term Earth system heat gainover the period 1971–2018, with a total heat gain of 358±37 ZJ,which is equivalent to a global heating rate of 0.47±0.1 W m−2.Over the period 1971–2018 (2010–2018), the majority of heat gain is reportedfor the global ocean with 89 % (90 %), with 52 % for both periods inthe upper 700 m depth, 28 % (30 %) for the 700–2000 m depth layer and 9 % (8 %) below 2000 m depth. Heat gain over land amounts to 6 %(5 %) over these periods, 4 % (3 %) is available for the melting ofgrounded and floating ice, and 1 % (2 %) is available for atmospheric warming. Ourresults also show that EEI is not only continuing, but also increasing: the EEIamounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization ofclimate, the goal of the universally agreed United Nations Framework Convention on ClimateChange (UNFCCC) in 1992 and the ParisAgreement in 2015, requires that EEI be reduced to approximately zero toachieve Earth's system quasi-equilibrium. The amount of CO2 in theatmosphere would need to be reduced from 410 to 353 ppm to increase heatradiation to space by 0.87 W m−2, bringing Earth back towards energybalance. This simple number, EEI, is the most fundamental metric that thescientific community and public must be aware of as the measure of how wellthe world is doing in the task of bringing climate change under control, andwe call for an implementation of the EEI into the global stocktake based onbest available science. Continued quantification and reduced uncertaintiesin the Earth heat inventory can be best achieved through the maintenance ofthe current global climate observing system, its extension into areas ofgaps in the sampling, and the establishment of an international framework forconcerted multidisciplinary research of the Earth heat inventory aspresented in this study. This Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/, last access: 7 August 2020) under the DOIhttps://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2(von Schuckmann et al., 2020). 
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  6. null (Ed.)
    Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution inresponse to different climate scenarios and assess the mass loss that would contribute tofuture sea level rise. However, there is currently no consensus on estimates of the future massbalance of the ice sheet, primarily because of differences in the representation of physicalprocesses, forcings employed and initial states of ice sheet models. This study presentsresults from ice flow model simulations from 13 international groups focusing on the evolutionof the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet ModelIntercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from theCoupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climatemodel results. Simulations of the Antarctic ice sheet contribution to sea level rise in responseto increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent(SLE) under Representative ConcentrationPathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment withconstant climate conditions and should therefore be added to the mass loss contribution underclimate conditions similar to present-day conditions over the same period. The simulated evolution of theWest Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighingthe increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelfcollapse, here assumed to be caused by large amounts of liquid water ponding at the surface ofice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without iceshelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, thecalibration of these melt rates based on oceanic conditions taken outside of ice shelf cavitiesand the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario basedon two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared tosimulations done under present-day conditions for the two CMIP5 forcings used and displaylimited mass gain in East Antarctica. 
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  7. The internal state of an organism influences its perception of attractive or aversive stimuli and thus promotes adaptive behaviors that increase its likelihood of survival. The mechanisms underlying these perceptual shifts are critical to our understanding of how neural circuits support animal cognition and behavior. Starved flies exhibit enhanced sensitivity to attractive odors and reduced sensitivity to aversive odors. Here, we show that a functional remodeling of the olfactory map is mediated by two parallel neuromodulatory systems that act in opposing directions on olfactory attraction and aversion at the level of the first synapse. Short neuropeptide F sensitizes an antennal lobe glomerulus wired for attraction, while tachykinin (DTK) suppresses activity of a glomerulus wired for aversion. Thus we show parallel neuromodulatory systems functionally reconfigure early olfactory processing to optimize detection of nutrients at the risk of ignoring potentially toxic food resources.

     
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