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The observed partitioning of poleward heat transport between atmospheric and oceanic heat transports (AHT and OHT) is compared to that in coupled climate models. Model ensemble mean poleward OHT is biased low in both hemispheres, with the largest biases in the Southern Hemisphere extratropics. Poleward AHT is biased high in the Northern Hemisphere, especially in the vicinity of the peak AHT near 40°N. The significant model biases are persistent across three model generations (CMIP3, CMIP5, CMIP6) and are insensitive to the satellite radiation and atmospheric reanalyzes products used to derive observational estimates of AHT and OHT. Model biases in heat transport partitioning are consistent with biases in the spatial structure of energy input to the ocean and atmosphere. Specifically, larger than observed model evaporation in the tropics adds excess energy to the atmosphere that drives enhanced poleward AHT at the expense of weaker OHT. The equator‐to‐pole contrast of solar radiation entering the climate system drives the large‐scale oceanic and atmospheric circulations that, in turn, move heat from the equator to the poles to moderate latitudinal temperature contrasts. The ocean moves the majority of heat in the tropics whereas the atmosphere moves the vast majority of heat in the mid‐ and polar‐latitudes. We demonstrate that, on average, state‐of‐the‐art climate models representing both oceanic and atmospheric circulations simulate too little oceanic heat transport and too much atmospheric heat transport relative to observational estimates. These model biases in the atmosphere‐ocean partitioning of poleward heat transport are persistent across three generations of climate model ensembles spanning 20 years of progress in climate modeling and are insensitive to the choice of datasets used to calculate observed heat transports. The model biases are consistent with stronger than observed surface evaporation in the tropics which enhances atmospheric heat transport at the expense of oceanic heat transport. Climate models simulate too little poleward oceanic heat transport and too much poleward atmospheric heat transport in the extratropicsModel biases in heat transport partitioning are persistent across model generation and are insensitive to the observational data sets usedStronger than observed evaporation in models enhances atmospheric heat transport at the expense of oceanic heat transport Climate models simulate too little poleward oceanic heat transport and too much poleward atmospheric heat transport in the extratropics Model biases in heat transport partitioning are persistent across model generation and are insensitive to the observational data sets used Stronger than observed evaporation in models enhances atmospheric heat transport at the expense of oceanic heat transport

Downward longwave radiation (DLR) is often assumed to be an independent forcing on the surface energy budget in analyses of Arctic warming and land‐atmosphere interaction. We use radiative kernels to show that the DLR response to forcing is largely determined by surface temperature perturbations. We develop a method by which vertically integrated versions of the radiative kernels are combined with surface temperature and specific humidity to estimate the surface DLR response to greenhouse forcing. Through a decomposition of the DLR response, we estimate that changes in surface temperature produce at least 63% of the clear‐sky DLR response in greenhouse forcing, while the changes associated with clouds account for only 11% of the full‐sky DLR response. Our results suggest that surface DLR is tightly coupled to surface temperature; therefore, it cannot be considered an independent component of the surface energy budget. Longwave radiation, often referred to as “thermal” or “infrared” radiation, emitted downward by Earth's atmosphere is a primary contributor to the surface energy budget. Numerous studies have invoked longwave radiation as a driver of surface warming. This paper shows that this line of reasoning fails to account for the strong control surface temperature exerts on longwave radiation. Using radiative kernels, matrices that quantify the longwave radiation response to a climate perturbation (like global warming), we argue that any surface temperature anomaly will generate a downward longwave radiation response. This constitutes a feedback between the Earth's surface and its atmosphere. The kernels show large longwave responses to perturbations in the lowest part of the atmosphere and almost no response to perturbations at high levels; by vertically integrating the kernels, we can ignore the vertical structure of climate perturbations. Using this modification, we predict the longwave radiation response to a warming world using only the surface changes. Our prediction agrees with climate model output, suggesting that the longwave radiation response is determined primarily by surface temperature. Further, the cloud contribution to changes in longwave radiation is small. These results provide clarity on how changes in the surface energy budget should be analyzed. The surface downward longwave radiation (DLR) response to forcing is determined by surface temperatureVertically integrated radiative kernels explain 71–84% of the variance in the DLR response to greenhouse gas forcingChanges in cloud cover contribute only 11% of the DLR response to greenhouse gas forcing

Arctic warming under increased CO2peaks in winter, but is influenced by summer forcing via seasonal ocean heat storage. Yet changes in atmospheric heat transport into the Arctic have mainly been investigated in the annual mean or winter, with limited focus on other seasons. We investigate the full seasonal cycle of poleward heat transport modeled with increased CO2or with individually applied Arctic sea‐ice loss and global sea‐surface warming. We find that a winter reduction in dry heat transport is driven by Arctic sea‐ice loss and warming, while a summer increase in moist heat transport is driven by sub‐Arctic warming and moistening. Intermodel spread in Arctic warming controls spread in seasonal poleward heat transport. These seasonal changes and their intermodel spread are well‐captured by down‐gradient diffusive heat transport. While changes in moist and dry heat transport compensate in the annual‐mean, their opposite seasonality may support non‐compensating effects on Arctic warming. The Arctic is warming much faster than the rest of the planet in response to rising greenhouse gas concentrations. Because Arctic warming peaks in winter, many studies have focused on the wintertime processes amplifying Arctic warming. However, others have found that summer atmospheric heating also contributes to winter warming by melting sea ice and storing heat in the ocean until it is released to the atmosphere in winter. Here we study changes in all seasons for one source of atmospheric heating in the Arctic—atmospheric heat transport from lower latitudes. Using climate model simulations, we find that heat and moisture are transported away from the regions that warm and moisten the most in response to rising greenhouse gas concentrations. The Arctic warms more than lower latitudes in winter, which reduces heat transport to the Arctic in winter. Atmospheric moisture increases most in late summer at lower latitudes, driving increased moisture transport in late summer from lower latitudes to the Arctic. We suggest that changes in heat and moisture transport may impact Arctic warming differently due to their opposite seasonality: by producing a larger change in surface solar absorption, summer changes in moisture transport may outweigh winter changes in heat transport. Sea‐ice loss reduces dry heat transport to the Arctic in winter; sub‐Arctic warming increases latent heat transport to the Arctic in summerIntermodel spread in Arctic warming controls intermodel spread in seasonal heat transport changesThe seasonal pattern of poleward heat transport change is well‐captured by down‐gradient diffusion of temperature and moisture anomalies Sea‐ice loss reduces dry heat transport to the Arctic in winter; sub‐Arctic warming increases latent heat transport to the Arctic in summer Intermodel spread in Arctic warming controls intermodel spread in seasonal heat transport changes The seasonal pattern of poleward heat transport change is well‐captured by down‐gradient diffusion of temperature and moisture anomalies

The impact of mountains on stratospheric circulation is explored using the Whole Atmosphere Community Climate Model. The “Mongolian mountains” decrease the boreal winter stratospheric jet strength by ∼1/3 and increase the frequency of major sudden stratospheric warmings from 0.08 year−1to the observed 0.60 year−1. These changes are twice the magnitude of the impacts of the Tibetan plateau and Himalayas. Consistent with the decrease in the zonal jet, there is enhanced Eliassen‐Palm flux convergence; this is predominantly from changes in wave propagation pathways through changes to the upper troposphere circulation, not from an increased amplitude of planetary waves reaching the stratosphere. The Mongolian mountains have the greater impact on upper tropospheric circulation due to their meridional location. The Rocky Mountains have no significant impact on the stratospheric jet. Changes in wave propagation in response to the Mongolian mountains are similar to those associated with major sudden stratospheric warming events in observations. The stratosphere is a layer of the atmosphere far from the Earth's surface (10–50 km above the surface), but changes in stratospheric circulation, particularly events known as sudden stratospheric warmings, affect the weather and climate at the surface. By flattening individual mountain regions in a climate model that extends from the Earth's surface far past the stratosphere, we study the effects of mountains on stratospheric circulation and the frequency of sudden stratospheric warming events. We find that the presence of the Mongolian mountains weakens the stratospheric jet by a third of its strength and creates 6 times more warming events as there would be without these mountains. The impact of the Mongolian mountains is about twice as large as the impact of the larger and more expansive Tibetan plateau and Himalaya. Mountains are a source of planetary‐scale atmospheric waves that propagate upward into the stratosphere; we find that the mountain effect on the stratosphere is largely because the mountains alter the pathway that all waves take as they propagate toward the stratosphere, through the influence the mountains have on circulation lower down in the atmosphere. We find similar anomalous wave propagation during sudden warming events in the model and observations. The Rossby refractive index can provide a positive feedback on stratospheric zonal wind changes via altered wave propagation pathwaysThe Mongolian mountains have twice the impact on stratospheric flow than the Tibetan plateau and HimalayasSudden stratospheric warmings dramatically reduce in frequency without the Mongolian mountains

Novel precipitation event data sets are created by tracking 3‐hourly observed rainfall in both time and space in the TRMM 3B42 and ERA‐Interim data sets. Relative to TRMM, ERA‐Interim data undersimulate the total number of events (factor of ∼0.5), and oversimulate the frequency of events lasting >5 days (factor of 1.6). Longer‐lasting events tend to have larger spatial footprints and higher intensity precipitation at any point in their lifetime, and thus contribute significantly more to total precipitation than shorter events. Precipitation changes in selected tropical and subtropical regions are attributed to different event characteristics: some to changes in event rainfall intensity, others to changes in the number of events. In the 40°S–40°N spatial average, the number of events lasting 1–5 days significantly increased from 1998 to 2014 in both the TRMM 3B42 and ERA‐Interim data. The event data sets, analysis scripts, and selected processed data are freely available online. Personal experience tells us that rain occurs in individual events, yet when researchers study rainfall in observations and models we do not tend to focus on “event characteristics.” Our work aims to change this, by presenting an analysis of event characteristics for all rain events that happened between 40°S and 40°N from 1980 to 2015. We look at how long events last (as they move through space), the average spatial footprint, or size, of events, and how much rain fell in total in an event. We set the stage for future work studying how “total event rainfall” may change in future climates, which may be crucial for estimating changes to the likelihood of flooding. Precipitation events are tracked in time and space over the whole globe for 1998–2014Relative to TRMM 3B42, ERA‐Interim oversimulates average event duration and spatial footprint, and undersimulates average event intensityThe number of 1–5 day events between 40 degrees S and 40 degrees N in the TRMM and ERA‐Interim data has increased over the last two decades

Radiative feedbacks robustly vary over time in transient warming simulations. Published studies offer two explanations: (i) evolving patterns of ocean heat uptake (OHU) or radiative forcing give rise to OHU or forcing “efficacies” and (ii) evolving patterns of surface temperature change. This study seeks to determine whether these explanations are indeed distinct. Using an idealized framework of an aquaplanet atmosphere‐only model, we show that radiative feedbacks depend on the pattern of climate forcing. Yet the same feedbacks arise when the temperature pattern induced by that climate forcing is prescribed in the absence of any forcing. These findings suggest the perspective that feedbacks are influenced by efficacies of forcing and OHU is equivalent to the perspective that feedbacks are dependent on the temperature patterns induced by those forcings. Prescribed surface temperature simulations are thus valuable for studying the temporal evolution of radiative feedbacks. Radiative feedbacks predominantly depend on the spatial pattern of surface temperature change, regardless of how that pattern is forcedClimate model experiments using prescribed sea surface temperature patterns are useful to study radiative feedbacks and climate sensitivityUniform warming simulations such as the amip4K runs produce different feedbacks than under polar amplified warming

Injection of sulfate aerosols into the stratosphere has the potential to reduce the climate impacts of global warming, including sea level rise (SLR). However, changes in atmospheric and oceanic circulation that can significantly influence the rate of basal melting of Antarctic marine ice shelves and the associated SLR have not previously been considered. Here we use a fully coupled global climate model to investigate whether rapidly increasing stratospheric sulfate aerosol concentrations after a period of global warming could preserve Antarctic ice sheets by cooling subsurface ocean temperatures. We contrast this climate engineering method with an alternative strategy in which all greenhouse gases (GHG) are returned to preindustrial levels. We find that the rapid addition of a stratospheric aerosol layer does not effectively counteract surface and upper level atmospheric circulation changes caused by increasing GHGs, resulting in continued upwelling of warm water in proximity of ice shelves, especially in the vicinity of the already unstable Pine Island Glacier in West Antarctica. By contrast, removal of GHGs restores the circulation, yielding relatively cooler subsurface ocean temperatures to better preserve West Antarctica. Sulfate aerosol injection allows warm Southern Ocean water to reach ice shelvesRisk of Antarctic ice sheet instability possible without surface warmingQuantitative assessment of sea level rise under aerosol injections needed

We examine the evidence for large‐scale tropical hydroclimate changes over the Common Era based on a compilation of 67 tropical hydroclimate records from 55 sites and assess the consistency between the reconstructed hydroclimate changes and those simulated by transient model simulations of the last millennium. Our synthesis of the proxy records reveals several regionally coherent patterns on centennial time scales. From 800 to 1000 CE, records from the eastern Pacific and parts of Mesoamerica indicate a pronounced drying event relative to background conditions of the Common Era. In addition, 1400–1700 CE is marked by pronounced hydroclimate changes across the tropics, including dry and/or isotopically enriched conditions in South and East Asia, wet and/or isotopically depleted conditions in the central Andes and southern Amazon in South America, and fresher and/or isotopically depleted conditions in the Maritime Continent. We find notable dissimilarities between the regional hydroclimate changes and global‐scale and hemispheric‐scale temperature reconstructions, indicating that more work needs to be done to understand the mechanisms of the widespread tropical hydroclimate changes during the LIA. Apropos to previous interpretations of large‐scale reorganization of tropical Pacific climate during the LIA, we do not find support for a large‐scale southward shift of the Pacific Intertropical Convergence Zone, while evidence for a strengthened Pacific Walker Circulation and/or an equatorward contraction of the monsoonal Asian‐Australian rain belt exists from limited geographic regions but require additional paleoclimate constraints. Transient climate model simulations exhibit weak forced long‐term tropical rainfall changes over the last millennium but provide several important insights to the proxy reconstructions. A synthesis of 67 tropical hydroclimate records from 55 sites indicate several regionally coherent patterns of change in the Common EraRobust patterns include a regional drying event from 800 to 1000 CE and a range of tropical hydroclimate changes ∼1400–1700 CETransient model simulations provide several new insights to the proxy reconstructions A synthesis of 67 tropical hydroclimate records from 55 sites indicate several regionally coherent patterns of change in the Common Era Robust patterns include a regional drying event from 800 to 1000 CE and a range of tropical hydroclimate changes ∼1400–1700 CE Transient model simulations provide several new insights to the proxy reconstructions

AbstractA new model for the upper North Atlantic Ocean is presented and used to hindcast the SST from 1950 to 1988. The model consists of a matrix of one-dimensional (independent) columns in which a variable-depth, bulk mixed layer overlies a diffusive convective thermocline. The climatological annual cycle of heat flux convergence by the oceanic circulation is implicitly included in the formulation of the forcing. The 39-yr control integration of the model includes as surface forcing the shortwave and net longwave radiation from a control integration of the community climate model. Sensible and latent heat fluxes are determined from instantaneous values of surface temperature, humidity, and wind speed from the atmospheric model, and the SST simulated by the ocean model using the bulk formulae. The hindcast is performed by repeating the control integration, adding the observed, monthly mean surface anomalies in surface temperature, humidity, and wind speed for the period 1950–88. Thus, the simulated SST anomalies are generated explicitly by anomalies in the latent and sensible heat fluxes. A separate hindcast integration is presented, using as forcing the “observed” sensible plus latent beat flux anomalies rather than the surface atmospheric field anomalies to demonstrate that the major results are not predetermined by the formulation of the coupling.The ability of the, model to hindcast the wintertime interannual variations in SST is demonstrated by simple correlations with observed anomalies and by comparing the composite of warm and cold events observed with those simulated by the model. There is a good quantitative agreement between simulated and observed SST anomalies throughout most of the North Atlantic Ocean. Since the model formulation explicitly excludes any effects due to anomaliesin the ocean advection, our results confirm the hypothesis that wintertime interannual to subdecadal variability in SST is mainly due to local anomalies in the air-sea flux of sensible and latent heat and not to anomalies in oceanic advection. Significant disagreement between hindcast and simulated SST anomalies is limited to a small region extending from Cape Hatteras to Nova Scotia along the U.S. coast. Here, the observed surface flux anomalies are anticorrelated with the SST anomalies, implicating important changes in oceanic advection in the generation of interannual wintertime SST and surface flux anomalies.Both the sensible and latent heat flux anomalies are shown to contribute substantially to the wintertime anomalies in SST in the subpolar Atlantic, while the heat flux anomalies are predominantly determined by the latent heat flux in the subtropics. Entrainment anomalies contribute to a lesser extent to the mixed layer temperature anomalies throughout the basin. Sensitivity studies are performed to highlight the atmospheric processes and variability that account for the surface heat flux anomalies.

The authors examine the natural variability of the arctic climate system simulated by two very different models: the Geophysical Fluid Dynamics Laboratory (GFDL) global climate model, and an area-averaged model of the arctic atmosphere–sea ice–upper-ocean system called the polar cap climate model, the PCCM. A 1000-yr integration of the PCCM is performed in which the model is driven by a prescribed, stochastic atmospheric energy flux convergence (D), which has spectral characteristics that are identical to the spectra of the observed D.The standard deviation of the yearly mean sea ice thickness from this model is 0.85 m; the mean sea ice thickness is 3.1 m. In contrast, the standard deviation of the yearly averaged sea ice thickness in the GFDL climate model is found to be about 6 of the climatological mean thickness and only 24 of that simulated by the PCCM.

Here 11 years of surface data (1961–72, excluding 1963) taken at ocean weather ship N (OWS N) are analyzed. OWS N is located in the subtropical eastern Pacific Ocean (140°W, 30°N). Bulk formulas are employed to calculate each component of the surface heat flux (sensible, latent, longwave, and shortwave) from the 3-h measurements of sea surface temperature (SST), air temperature, surface humidity, wind speed, and cloudiness. Analyses are performed on fluxes averaged over daily and monthly intervals. Results indicate a large fraction of the variance in net surface energy flux is associated with anomalies in the latent heat flux; the latter are principally due to variability in the surface wind speed. Cross correlation and regression analyses of monthly anomalies of SST and SST tendency (∂SST/∂t) with the surface heat flux components indicate over 50 of the variance in SST-tendency anomalies is accounted for by local anomalies in the netsurface energy flux.

AbstractThe low-frequency natural variability of the arctic climate system is modeled using a single-column, energy balance model of the atmosphere. sea ice, and upper-ocean system. Variability in the system is induced by forcing with realistic, random perturbations in the atmospheric energy transport and cloudiness. The model predicts that the volume of perennial sea ice varies predominantly on decadal timescales, while other arctic climate variables vary mostly on intraannual and interannual timescales. The variance of the simulated sea ice volume is most sensitive to perturbations of the atmospheric forcing in late spring, at the onset of melt. The variance of sea ice volume increases with the mean sea ice thickness and with the number of layers resolved in the sea ice model. This suggests that much of the simulated variance develops when the surface temperature decouples from the sea ice interior during the late spring, when melting snow abruptly exposes the sea ice surface and decreases the surface albedo.The minimum model requirements to simulate the natural variability in the arctic climate are identified. The implications of the low-frequency, natural variability in sea ice volume for detecting a climate change are discussed. Finally, calculations suggest that the variability in the thermodynamic forcing of the polar cap could lead to a freshening in the North Atlantic that is comparable to the freshening associated with the Great Salinity Anomaly.

Objective:To study plasma concentrations of interleukin 6 (IL-6) and interleukin 8 (IL-8) in patients with splanchnic hypoxia, as documented by gastric intramucosal measurements (pH-i), during major abdominal surgery and the relationship between IL-6 and IL-8 concentrations and postoperative complications as well as clinical outcome.

The increasing frequency of very high temperatures driven by global warming has motivated growing interest in how the probability distribution of summertime temperatures will evolve in the future. Climate models forced by increasing CO2simulate increasing monthly‐averaged temperature variance across the midlatitudes. In this study we present evidence that these projections are credible and driven primarily by the magnitude of local warming. A first‐principles analytic theory reproduces the increased midlatitude summertime temperature variance in climate models extremely well by considering only the warming‐induced change in the climatological vapor pressure deficit. The impacts of local warming on saturation specific and relative humidity are shown to have roughly equal contributions to increases in summertime temperature variance. The vegetation response to increasing CO2is found to be an important contributor to the uncertainty in modeled temperature variance change, highlighting the role of plants in shaping the summertime temperature distribution. Extreme summertime temperatures are a focal point for the impacts of climate change. Climate models driven by increasing CO2emissions project increasing summertime temperature variability by the end of the 21stcentury. If credible, these increases imply that extreme summertime temperatures will become even more frequent than a simple shift in the contemporary probability distribution would suggest. Given the impacts of extreme temperatures on public health, food security, and the global economy, it is of great interest to understand whether the projections of increased temperature variance are credible. In this study, we use a theoretical model of the land surface to demonstrate that the large increases in summertime temperature variance projected by climate models are credible, predictable from first principles, and driven by the effects of warmer temperatures on evapotranspiration. We also find that the response of plants to increased CO2and mean warming is important to the projections of increased temperature variability. Summertime temperature variance over land increases with local mean temperature in contemporary global climate modelsA theoretical model captures these increases using only projected changes in temperature and relative humidity from global climate modelsUncertainties in climate sensitivity and plant processes control the spread of climate model summertime temperature variance change

The lapse rate feedback is the dominant driver of stronger warming in the Arctic than the Antarctic in simulations with increased CO2. While Antarctic surface elevation has been implicated in promoting a weaker Antarctic lapse rate feedback, the mechanisms in which elevation impacts the lapse rate feedback are still unclear. Here we suggest that weaker Antarctic warming under CO2forcing stems from shallower, less intense climatological inversions due to limited atmospheric heat transport above the ice sheet elevation and elevation‐induced katabatic winds. In slab ocean model experiments with flattened Antarctic topography, stronger climatological inversions support a stronger lapse rate feedback and annual mean Antarctic warming comparable to the Arctic under CO2doubling. Unlike the Arctic, seasonality in warming over flat Antarctica is mainly driven by a negative shortwave cloud feedback, which exclusively dampens summer warming, with a smaller contribution from the winter‐enhanced lapse rate feedback. Models project stronger surface warming in the Arctic than the Antarctic under climate change. A climate feedback in which more warming occurs near the surface than at higher altitudes in the atmosphere promotes this stronger Arctic warming. Antarctica's surface elevation is thought to weaken this feedback in comparison to the Arctic, but how this occurs is unclear. Here we show that Antarctic elevation weakens surface warming by changing the base state vertical temperature structure. When Antarctic topography is flattened in model experiments, Antarctica experiences more warming under climate change, resembling Arctic warming. Similarly to the Arctic, flat Antarctica warms most during the winter, but this seasonality is driven by different climate feedbacks in the Arctic versus Antarctic. These results indicate the importance of base state temperatures for warming under climate change and suggest that strong polar amplification is possible without local sea ice loss. Antarctic elevation causes asymmetry in climatological inversions, lapse rate feedbacks, and warming between the polesIn model experiments with flattened Antarctica, strengthened inversions lead to stronger lapse rate feedback and Antarctic amplificationShortwave cloud feedback promotes seasonality in flat Antarctic warming; lapse rate feedback more strongly promotes seasonality in Arctic