A Formal Analysis of the Feedback Concept in Climate Models. Part I: Exclusive and Inclusive Feedback Analyses*

Abstract Climate sensitivity and feedback are key concepts if the complex behavior of climate response to perturbation is to be interpreted in a simple way. They have also become an essential tool for comparing global circulation models and assessing the reason for the spread in their results. The authors introduce a formal basic model to analyze the practical methods used to infer climate feedbacks and sensitivity from GCMs. The tangent linear model is used first to critically review the standard methods of feedback analyses that have been used in the GCM community for 40 years now. This leads the authors to distinguish between exclusive feedback analyses as in the partial radiative perturbation approach and inclusive analyses as in the “feedback suppression” methods. This review explains the hypotheses needed to apply these methods with confidence. Attention is paid to the more recent regression technique applied to the abrupt 2×CO2 experiment. A numerical evaluation of it is given, related to the Lyapunov analysis of the dynamical feature of the regression. It is applied to the Planck response, determined in its most strict definition within the GCM. In this approach, the Planck feedback becomes a dynamical feedback among others and, as such, also has a fast response differing from its steady-state profile.

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Tesserae on Venus may preserve evidence of fluvial erosion

Nature Communications ◽

10.1038/s41467-020-19336-1 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

S. Khawja ◽

R. E. Ernst ◽

C. Samson ◽

P. K. Byrne ◽

R. C. Ghail ◽

...

Keyword(s):

Climate Models ◽

High Surface ◽

Climatic Conditions ◽

Tectonic Deformation ◽

Fluvial Erosion ◽

Global Circulation ◽

Global Circulation Models ◽

Research Theme ◽

Wet Climate ◽

Indirect Technique

AbstractFluvial erosion is usually assumed to be absent on Venus, precluded by a high surface temperature of ~450 °C and supported by extensive uneroded volcanic flows. However, recent global circulation models suggest the possibility of Earth-like climatic conditions on Venus for much of its earlier history, prior to catastrophic runaway greenhouse warming. We observe that the stratigraphically oldest, geologically most complex units, tesserae, exhibit valley patterns morphologically similar to the patterns resulting from fluvial erosion on Earth. Given poor topographic resolution, we use an indirect technique to recognize valleys, based on the pattern of lava flooding of tesserae margins by adjacent plains volcanism. These observed valley patterns are attributed to primary geology, tectonic deformation, followed by fluvial erosion (and lesser wind erosion). This proposed fluvial erosion in tesserae provides support for climate models for a cool, wet climate on early Venus and could be an attractive research theme for future Venus missions.

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Modelling melt ponds in Global Circulation Models

10.5194/egusphere-egu2020-21530 ◽

2020 ◽

Author(s):

Jean Sterlin ◽

Thierry Fichefet ◽

François Massonnet ◽

Olivier Lecomte ◽

Martin Vancoppenolle

Keyword(s):

Aspect Ratio ◽

Sea Ice ◽

Climate Models ◽

Arctic Sea Ice ◽

The Arctic ◽

Global Circulation ◽

Melt Pond ◽

Global Circulation Models ◽

Melt Ponds ◽

The Impact

Melt ponds appear during the Arctic summer on the sea ice cover when meltwater and liquid precipitation collect in the depressions of the ice surface. The albedo of the melt ponds is lower than that of surrounding ice and snow areas. Consequently, the melt ponds are an important factor for the ice-albedo feedback, a mechanism whereby a decrease in albedo results in greater absorption of solar radiation, further ice melt, and lower albedos&#160;To account for the effect of melt ponds on the climate, several numerical schemes have been introduced for Global Circulation Models. They can be classified into two groups. The first group makes use of an explicit relation to define the aspect ratio of the melt ponds. The scheme of Holland et al. (2012) uses a constant ratio of the melt pond depth to the fraction of sea ice covered by melt ponds. The second group relies on theoretical considerations to deduce the area and volume of the melt ponds. The scheme of Flocco et al. (2012) uses the ice thickness distribution to share the meltwater between the ice categories and determine the melt ponds characteristics.Despite their complexity, current melt pond schemes fail to agree on the trends in melt pond fraction of sea ice area during the last decades. The disagreement casts doubts on the projected melt pond changes. It also raises questions on the definition of the physical processes governing the melt ponds in the schemes and their sensitivity to atmospheric surface conditions.In this study, we aim at identifying 1) the conceptual difference of the aspect ratio definition in melt pond schemes; 2) the role of refreezing for melt ponds; 3) the impact of the uncertainties in the atmospheric reanalyses. To address these points, we have run the Louvain-la-Neuve Ice Model (LIM), part of the Nucleus for European Modelling of the Ocean (NEMO) version 3.6 along with two different atmospheric reanalyses as surface forcing sets. We used the reanalyses in association with Holland et al. (2012) and Flocco et al. (2012) melt pond schemes. We selected Holland et al. (2012) pond refreezing formulation for both schemes and tested two different threshold temperatures for refreezing.&#160;From the experiments, we describe the impact on Arctic sea ice and state the importance of including melt ponds in climate models. We attempt at disentangling the separate effects of the type of melt pond scheme, the refreezing mechanism, and the atmospheric surface forcing method, on the climate. We finally formulate a recommendation on the use of melt ponds in climate models.&#160;

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Do GCMs predict the climate ... or macroweather?

Earth System Dynamics ◽

10.5194/esd-4-439-2013 ◽

2013 ◽

Vol 4 (2) ◽

pp. 439-454 ◽

Cited By ~ 24

Author(s):

S. Lovejoy ◽

D. Schertzer ◽

D. Varon

Keyword(s):

Climate Models ◽

Great Majority ◽

Nonlinear Dynamical ◽

Global Circulation ◽

Global Circulation Models ◽

Scale Temperature ◽

Continuous Background ◽

Climate Forcings ◽

Spectral Variance ◽

Global Fluctuations

Abstract. We are used to the weather–climate dichotomy, yet the great majority of the spectral variance of atmospheric fields is in the continuous "background" and this defines instead a trichotomy with a "macroweather" regime in the intermediate range from ≈10 days to 10–30 yr (≈100 yr in the preindustrial period). In the weather, macroweather and climate regimes, exponents characterize the type of variability over the entire regime and it is natural to identify them with qualitatively different synergies of nonlinear dynamical mechanisms that repeat scale after scale. Since climate models are essentially meteorological models (although with extra couplings) it is thus important to determine whether they currently model all three regimes. Using last millennium simulations from four GCMs (global circulation models), we show that control runs only reproduce macroweather. When various (reconstructed) climate forcings are included, in the recent (industrial) period they show global fluctuations strongly increasing at scales > ≈10–30 yr, which is quite close to the observations. However, in the preindustrial period we find that the multicentennial variabilities are too weak and by analysing the scale dependence of solar and volcanic forcings, we argue that these forcings are unlikely to be sufficiently strong to account for the multicentennial and longer-scale temperature variability. A likely explanation is that the models lack important slow "climate" processes such as land ice or various biogeochemical processes.

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Global Circulation Models (GCMs) Simulate the Current Temperature Only If the Shortwave Radiation Anomaly of the 2000s Has Been Omitted

Current Journal of Applied Science and Technology ◽

10.9734/cjast/2021/v40i1731433 ◽

2021 ◽

pp. 45-52

Author(s):

Antero Ollila

Keyword(s):

Climate Change ◽

General Circulation ◽

Climate Models ◽

Coupled Model ◽

General Circulation Models ◽

Scientific Basis ◽

Shortwave Radiation ◽

Global Circulation ◽

Global Circulation Models ◽

Paris Climate Agreement

The research article of Gillett et al. was published in Nature Climate Change (NCC) in March 2021. The objective of the NCC study was to simulate human-induced forcings to warming by applying 13 CMIP6 (Coupled Model Intercomparison Project Phase 6) climate models. NCC did not accept the author’s remarks as a “Matters arising” article. The purpose of this article is to detail the original three remarks and one additional remark: 1) the discrepancy between the graphs and reported numerical values, 2) the forcings of aerosols and clouds, 3) the positive water feedback, and 4) the calculation basis of the Paris agreement. The most important finding is that General Circulation Models (GCMs) used in simulations omit the significant shortwave anomaly from 2001 to 2019, which causes a temperature error of 0.3°C according to climate change physics of Gillett et al. For the year 2019, this error is 0.8°C showing the magnitude of shortwave anomaly impact. The main reason for this error turns out to be the positive water feedback generally applied in climate models. The scientific basis of the Paris climate agreement is faulty for the same reason.

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A Formal Analysis of the Feedback Concept in Climate Models. Part III: Feedback Dynamics and the Seasonal Cycle in a Floquet Analysis

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0364.1 ◽

2015 ◽

Vol 72 (9) ◽

pp. 3574-3596

Author(s):

Alain Lahellec ◽

Krista Reimer

Keyword(s):

Seasonal Cycle ◽

Climate Models ◽

Water Cycle ◽

Slow Component ◽

Spatial Scales ◽

Formal Analysis ◽

Climate Feedback ◽

Climate Feedbacks ◽

Formal Framework ◽

1D Model

Abstract This article introduces a new decomposition of climate feedback mechanisms based on their characteristic times. As the last of a series of three, it complements the first two parts by Lahellec and Dufresne to give a comprehensive review of climate feedbacks that will help to ensure consistency between practice and theory. In Parts I and II, analysis of the climate response to perturbations at the large spatial scales and time scales necessary to obtain linearity restricted the characterization to the slow components of the response. This part incorporates the fast mechanisms’ impact on the climate feedbacks, bringing the seasonal cycle into the analysis. Thanks to the Floquet theory, the authors could extend the formal framework of Parts I and II to incorporate the fast mechanisms. An illustration of the formal results with a simple 1D model highlights a clear distinction between the role of fast (intraseasonal) and slow (decadal) feedbacks, with an application to the water-cycle feedback of Part II. The same implementation of the Gâteaux difference in LMDZ, the GCM of LMD, as in Part II is used for comparing results with the authors’ toy model. This comparison essentially validates the Floquet decomposition obtained with the toy model: the fast component linked to precipitation is contributing negatively to the water-cycle feedback while the slow component is building up the positive feedback. The comparison also provides further insight on the sensitivity of models’ precipitation to climate warming.

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Parameterization Of Boundary Conditions Between The Atmosphere and Cryosphere

Annals of Glaciology ◽

10.1017/s0260305500009174 ◽

1990 ◽

Vol 14 ◽

pp. 348

Author(s):

E.M. Morris ◽

R.J. Harding

Keyword(s):

Boundary Conditions ◽

Climate Models ◽

Coastal Region ◽

Distributed Model ◽

Model Parameters ◽

Global Circulation ◽

Global Circulation Models ◽

Ice Surface ◽

Temporal Averaging ◽

Energy Exchanges

Parameterization of the boundary conditions between the atmosphere and cryosphere is an important part of the general problem of modelling climatic change. It is necessary to define the mass, momentum and energy exchanges at the ice/atmosphere interface in order (i) to use atmospheric global circulation models (AGCMs) to predict future climate and (ii) to use snow, glacier or ice-sheet models to predict the corresponding response of the cryosphere. The physics of the boundary processes are fairly well known; the difficulty lies in choosing the appropriate space and time scales for modelling and in understanding the changes in the effective values of the model parameters which may be produced by spatial and temporal averaging. Sensible heat, water vapour and momentum are tranferred vertically in the boundary layer of the atmosphere by turbulent motion. Equations for these fluxes contain parameters, the so-called scaling lengths zH, ZE and z0. Net radiation input to snow or ice is controlled by the albedo of the surface, α These four parameters play a major role in defining the boundary conditions between the atmosphere and cryosphere. It is normally assumed that their values are constants, determined by the characteristics of the snow or ice surface alone. For example, climate models may set zH = Ze = z0 = 0.1 mm and α = 0.9 for smooth, fresh snow. However, in modelling practice it is often found that the effective values of the parameters, i.e. those values that give the best simulations, are also influenced by the level of variability in the meteorological conditions. The authors have made intensive micro-meteorological studies in the firn area of the Hintereisferner, Ötztal Alpen (Austria), on a frozen lake near Finse, Hardangervidda (Norway), and in the south-west coastal region of Greenland. Data from these field sites will be used to investigate the sensitivity of effective values of the boundary condition parameters to the choice of time scale using the Institute of Hydrology Distributed Model (IHDM).

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Gains and losses in surface solar radiation with dynamic aerosols in regional climate simulations for Europe

10.5194/gmd-2020-238 ◽

2020 ◽

Author(s):

Sonia Jerez ◽

Laura Palacios-Peña ◽

Claudia Gutiérrez ◽

Pedro Jiménez-Guerrero ◽

Jose María López-Romero ◽

...

Keyword(s):

Solar Radiation ◽

Atmospheric Aerosol ◽

Climate Models ◽

Regional Climate ◽

Wrf Model ◽

Regional Climate Models ◽

Surface Solar Radiation ◽

Global Circulation ◽

Global Circulation Models ◽

Gains And Losses

Abstract. The solar resource can be highly influenced by clouds and atmospheric aerosol, which has been named by the IPCC as the most uncertainty climate forcing agent. Nonetheless, Regional Climate Models (RCMs) hardly ever model dynamically atmospheric aerosol concentration and their interaction with radiation and clouds, in contrast to Global Circulation Models (GCMs). The objective of this work is to evince the role of the interactively modeling of aerosol concentrations and their interactions with radiation and clouds in Weather Research and Forecast (WRF) model simulations with a focus on summer mean surface downward solar radiation (RSDS) and over Europe. The results show that the response of RSDS is mainly led by the aerosol effects on cloudiness, which explain well the differences between the experiments in which aerosol-radiation and aerosol-radiation-cloud interactions are taken into account or not. Under present climate, a reduction about 5% in RSDS was found when aerosols are dynamically solved by the RCM, which is larger when only aerosol-radiation interactions are considered. However, for future projections, the inclusion of aerosol-radiation-cloud interactions results in the most negative RSDS change pattern (while with slight values), showing noticeable differences with the projections from either the other RCM experiments or from their driving GCM (which do hold some significant positive signals). Differences in RSDS among experiments are much more softer under clear-sky conditions.

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Vertical Heating Structures Associated with the MJO as Characterized by TRMM Estimates, ECMWF Reanalyses, and Forecasts: A Case Study during 1998/99 Winter

Journal of Climate ◽

10.1175/2009jcli3048.1 ◽

2009 ◽

Vol 22 (22) ◽

pp. 6001-6020 ◽

Cited By ~ 29

Author(s):

Xianan Jiang ◽

Duane E. Waliser ◽

William S. Olson ◽

Wei-Kuo Tao ◽

Tristan S. L’Ecuyer ◽

...

Keyword(s):

Indian Ocean ◽

Rain Rate ◽

Climate Models ◽

Global Climate ◽

Winter Season ◽

Tropical Rainfall Measuring Mission ◽

Radiative Heating ◽

Weather Forecasts ◽

Global Circulation ◽

Global Circulation Models

Abstract The Madden–Julian oscillation (MJO) is a fundamental mode of the tropical atmosphere variability that exerts significant influence on global climate and weather systems. Current global circulation models, unfortunately, are incapable of robustly representing this form of variability. Meanwhile, a well-accepted and comprehensive theory for the MJO is still elusive. To help address this challenge, recent emphasis has been placed on characterizing the vertical structures of the MJO. In this study, the authors analyze vertical heating structures by utilizing recently updated heating estimates based on the Tropical Rainfall Measuring Mission (TRMM) from two different latent heating estimates and one radiative heating estimate. Heating structures from two different versions of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses/forecasts are also examined. Because of the limited period of available datasets at the time of this study, the authors focus on the winter season from October 1998 to March 1999. The results suggest that diabatic heating associated with the MJO convection in the ECMWF outputs exhibits much stronger amplitude and deeper structures than that in the TRMM estimates over the equatorial eastern Indian Ocean and western Pacific. Further analysis illustrates that this difference might be due to stronger convective and weaker stratiform components in the ECMWF estimates relative to the TRMM estimates, with the latter suggesting a comparable contribution by the stratiform and convective counterparts in contributing to the total rain rate. Based on the TRMM estimates, it is also illustrated that the stratiform fraction of total rain rate varies with the evolution of the MJO. Stratiform rain ratio over the Indian Ocean is found to be 5% above (below) average for the disturbed (suppressed) phase of the MJO. The results are discussed with respect to whether these heating estimates provide enough convergent information to have implications on theories of the MJO and whether they can help validate global weather and climate models.

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Parameterization Of Boundary Conditions Between The Atmosphere and Cryosphere

Annals of Glaciology ◽

10.3189/s0260305500009174 ◽

1990 ◽

Vol 14 ◽

pp. 348-348

Author(s):

E.M. Morris ◽

R.J. Harding

Keyword(s):

Boundary Conditions ◽

Climate Models ◽

Coastal Region ◽

Distributed Model ◽

Model Parameters ◽

Global Circulation ◽

Global Circulation Models ◽

Ice Surface ◽

Temporal Averaging ◽

Energy Exchanges

Parameterization of the boundary conditions between the atmosphere and cryosphere is an important part of the general problem of modelling climatic change. It is necessary to define the mass, momentum and energy exchanges at the ice/atmosphere interface in order (i) to use atmospheric global circulation models (AGCMs) to predict future climate and (ii) to use snow, glacier or ice-sheet models to predict the corresponding response of the cryosphere. The physics of the boundary processes are fairly well known; the difficulty lies in choosing the appropriate space and time scales for modelling and in understanding the changes in the effective values of the model parameters which may be produced by spatial and temporal averaging.Sensible heat, water vapour and momentum are tranferred vertically in the boundary layer of the atmosphere by turbulent motion. Equations for these fluxes contain parameters, the so-called scaling lengths zH, ZE and z0. Net radiation input to snow or ice is controlled by the albedo of the surface, α These four parameters play a major role in defining the boundary conditions between the atmosphere and cryosphere. It is normally assumed that their values are constants, determined by the characteristics of the snow or ice surface alone. For example, climate models may set zH = Ze = z0 = 0.1 mm and α = 0.9 for smooth, fresh snow. However, in modelling practice it is often found that the effective values of the parameters, i.e. those values that give the best simulations, are also influenced by the level of variability in the meteorological conditions.The authors have made intensive micro-meteorological studies in the firn area of the Hintereisferner, Ötztal Alpen (Austria), on a frozen lake near Finse, Hardangervidda (Norway), and in the south-west coastal region of Greenland. Data from these field sites will be used to investigate the sensitivity of effective values of the boundary condition parameters to the choice of time scale using the Institute of Hydrology Distributed Model (IHDM).

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Streamflow estimation for six UK catchments under future climate scenarios

Hydrology Research ◽

10.2166/nh.2009.086 ◽

2009 ◽

Vol 40 (2-3) ◽

pp. 96-112 ◽

Cited By ~ 17

Author(s):

K. P. Chun ◽

H. S. Wheater ◽

C. J. Onof

Keyword(s):

Time Series ◽

Climate Models ◽

Climate Model ◽

Future Climate ◽

Rainfall Time Series ◽

Climate Scenarios ◽

Large Variability ◽

Global Circulation ◽

Global Circulation Models ◽

Rainfall Runoff Model

Possible changes in streamflow in response to climate variation are crucial for anthropological and ecological systems. However, estimates of precipitation under future climate scenarios are notoriously uncertain. In this article, rainfall time series are generated by the generalized linear model (GLM) approach in which stochastic time series are generated using alternative climate model output variables and potential evaporation series estimated by a temperature method. These have been input to a conceptual rainfall–runoff model (pd4-2par) to simulate the daily streamflows for six UK catchments for a set of climate scenarios using seven global circulation models (GCMs) and regional circulation models (RCMs). The performance of the combined methodology in reproducing observed streamflows is generally good. Results of future climate scenarios show significant variability between different catchments, and very large variability between different climate models. It is concluded that the GLM methodology is promising, and can readily be extended to support distributed hydrological modelling.

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