In this study we present a simple scheme for the diagnosis of the strength of climate feedback. The scheme is based on straightforward calculations using the conventional output of a general ...circulation model (GCM), and evaluates the major radiative feedbacks concerning the surface, clear‐sky atmosphere, and clouds. We place an emphasis on evaluating shortwave (SW) feedbacks. Assumptions involved in extracting the SW surface feedback are validated by accurate calculations and considered to be acceptable. The performance of our scheme is demonstrated via a doubled CO2 experiment. Compared to conventional methods, we can evaluate SW feedbacks more accurately while the evaluation of LW feedbacks is essentially similar between the two methods. The ready application of our scheme to the output of various GCMs should be of great use for multi‐model ensemble analyses, which contribute to reducing the uncertainty in future climate projections.
Byline: K. D. Williams (1,2), M. A. Ringer (1), C. A. Senior (1), M. J. Webb (1), B. J. McAvaney (3), N. Andronova (4), S. Bony (5), J. -L. Dufresne (5), S. Emori (6), R. Gudgel (7), T. Knutson (7), ...B. Li (4), K. Lo (8), I. Musat (5), J. Wegner (9), A. Slingo (2), J. F. B. Mitchell (1) Most of the uncertainty in the climate sensitivity of contemporary general circulation models (GCMs) is believed to be connected with differences in the simulated radiative feedback from clouds. Traditional methods of evaluating clouds in GCMs compare time--mean geographical cloud fields or aspects of present-day cloud variability, with observational data. In both cases a hypothetical assumption is made that the quantity evaluated is relevant for the mean climate change response. Nine GCMs (atmosphere models coupled to mixed-layer ocean models) from the CFMIP and CMIP model comparison projects are used in this study to demonstrate a common relationship between the mean cloud response to climate change and present-day variability. Although atmosphere--mixed-layer ocean models are used here, the results are found to be equally applicable to transient coupled model simulations. When changes in cloud radiative forcing (CRF) are composited by changes in vertical velocity and saturated lower tropospheric stability, a component of the local mean climate change response can be related to present-day variability in all of the GCMs. This suggests that the relationship is not model specific and might be relevant in the real world. In this case, evaluation within the proposed compositing framework is a direct evaluation of a component of the cloud response to climate change. None of the models studied are found to be clearly superior or deficient when evaluated, but a couple appear to perform well on several relevant metrics. Whilst some broad similarities can be identified between the 60degN--60degS mean change in CRF to increased CO.sub.2 and that predicted from present-day variability, the two cannot be quantitatively constrained based on changes in vertical velocity and stability alone. Hence other processes also contribute to the global mean cloud response to climate change. Author Affiliation: (1) Met Office, Hadley Centre for Climate Prediction and Research, FitzRoy Road, Exeter, EX1 3PB, UK (2) Environmental Systems Science Centre, University of Reading, Reading, UK (3) Bureau of Meteorology Research Centre, Sydney, Australia (4) Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, USA (5) Institut Pierre Simon Laplace, Paris, France (6) National Institute for Environmental Studies, Ibaraki, Japan (7) Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA (8) Goddard Institute for Space Studies, New York, USA (9) Max Planck Institute for Meteorology, Hamburg, Germany Article History: Registration Date: 09/08/2005 Received Date: 01/04/2005 Accepted Date: 05/08/2005 Online Date: 20/12/2005
Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth's climate system and its likely response to human and natural ...influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community.
The Model for Interdisciplinary Research on Climate (MIROC), an atmosphere‐ocean coupled general circulation model (AOGCM), has two versions with different resolutions, high (Hi‐Res) and medium ...(Mid‐Res). While their equilibrium climate sensitivities (ECS) to CO2 increases are similar, the transient climate response (TCR) of the Hi‐Res version is larger than that of the Mid‐Res version. The former shows the highest transient response among the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report (AR4) climate models. Our climate feedback analysis indicates that the higher TCR of the Hi‐Res version mainly comes from its larger ice‐albedo feedback (SFC‐SW) and lower ocean heat uptake (OHU). Since the Hi‐Res version shows better agreement with observation than the Mid‐Res version concerning the factors that affect the SFC‐SW and OHU, the TCR of the Hi‐Res version is not considered to be unrealistic compared to that of the Mid‐Res version. On the other hand, the two versions have similar SFC‐SW values and negligible OHU in ECS experiments performed by the atmosphere‐slab ocean coupled general circulation model (ASGCM). In the ASGCM, the difference in SFC‐SW between the two versions was likely suppressed due to artificial fluxes applied to the ocean and sea‐ice system.
The fruit size of melon ( Cucumis melo L. reticulatus) is determined by the amount of cell proliferation in the pericarp during early fruit development. During this stage, expression and activity of ...the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) gene is required for fruit growth. In this study, we performed a detailed analysis of the correlation between the expression of melon HMGR (Cm-HMGR) protein and cell division in the pericarp. Flow cytometric analysis revealed that the length of the cell division stage was correlated with the fruit size. Western gel blotting and tissue printing illustrated the temporal and spatial accumulation pattern of Cm-HMGR protein during fruit development. The accumulation of Cm-HMGR transiently increased at the beginning of the cell division stage in the pericarp, where active cell division occurred. The amount of Cm-HMGR was correlated with the length of the cell division period. These results strongly suggest that the expression of Cm-HMGR is involved in the determination of melon fruit size by regulating cell division during early fruit development.
With a global aerosol transport‐radiation model coupled to a general circulation model, changes in the meteorological parameters of clouds, precipitation, and temperature caused by the direct and ...indirect effects of aerosols are simulated, and its radiative forcing are calculated. A microphysical parameterization diagnosing the cloud droplet number concentration based on the Köhler theory is introduced into the model, which depends not only on the aerosol particle number concentration but also on the updraft velocity, size distributions, and chemical properties of each aerosol species and saturation condition of the water vapor. The simulated cloud droplet effective radius, cloud radiative forcing, and precipitation rate, which relate to the aerosol indirect effect, are in reasonable agreement with satellite observations. The model results indicate that a decrease in the cloud droplet effective radius by anthropogenic aerosols occurs globally, while changes in the cloud water and precipitation are strongly affected by a variation of the dynamical hydrological cycle with a temperature change by the aerosol direct and first indirect effects rather than the second indirect effect itself. However, the cloud water can increase and the precipitation can simultaneously decrease in regions where a large amount of anthropogenic aerosols and cloud water exist, which is a strong signal of the second indirect effect. The global mean radiative forcings of the direct and indirect effects at the tropopause by anthropogenic aerosols are calculated to be −0.1 and −0.9 W m−2, respectively. It is suggested that aerosol particles approximately reduce 40% of the increase in the surface air temperature by anthropogenic greenhouse gases on the global mean.
Simulated daily discharge derived from a relatively high-resolution (approximately 1.1-degree) general circulation model was used to investigate future projections of extremes in river discharge ...under global warming. The frequency of floods was projected to increase over many regions, except those including North America and central to western Eurasia. The drought frequency was projected to increase globally, while regions such as northern high latitudes, eastern Australia, and eastern Eurasia showed a decrease or no significant changes. Changes in flood and drought are not explained simply by changes in annual precipitation, heavy precipitation, or differences between precipitation and evapotranspiration. Several regions were projected to have increases in both flood frequency and drought frequency. Such regions show a decrease in the number of precipitation days, but an increase in days with heavy rain. Several regions show shifts in the flood season from springtime snowmelt to the summer period of heavy precipitation.
A land surface model (LSM), minimal advanced treatments of surface interaction and runoff (MATSIRO), has been developed for climate studies at the global and regional scales. The canopy has a single ...layer, whose albedo and bulk coefficients are evaluated on the basis of a multilayer canopy model. The fluxes are calculated from the energy balance at the ground and canopy surfaces in snow-free and snow-covered portions considering the subgrid snow distribution. The interception evaporation from canopy and the transpiration on the basis of photosynthesis are treated. A simplified TOPMODEL is used to calculate runoff. The snow has the variable number of layers from one to three in accordance with snow water equivalent (SWE), and the snow temperature is calculated by a thermal conduction equation. Besides, the snowmelt, the refreeze of snowmelt, and the freeze of rainfall in snow are taken into consideration. It is found in the PILPS 2e experiment that some parameters in the runoff scheme, such as the surface hydraulic conductivity and the river channel fraction, have a considerable impact on the partitioning of the surface runoff and the base flow. The snow albedo is prognosticated from the time passage since last snowfall and the snow temperature. The soil has five layers in this version, and the soil temperature, the soil moisture, and the frozen amount of moisture are calculated.
This study evaluates the tropical intraseasonal variability, especially the fidelity of Madden–Julian oscillation (MJO)simulations, in 14 coupled general circulation models (GCMs) participating in ...the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of daily precipitation from each model’s twentieth-century climate simulation are analyzed and compared with daily satellite-retrieved precipitation. Space–time spectral analysis is used to obtain the variance and phase speed of dominant convectively coupled equatorial waves, including the MJO, Kelvin, equatorial Rossby (ER), mixed Rossby–gravity (MRG), and eastward inertio–gravity (EIG) and westward inertio–gravity (WIG) waves. The variance and propagation of the MJO, defined as the eastward wavenumbers 1–6, 30–70-day mode, are examined in detail.
The results show that current state-of-the-art GCMs still have significant problems and display a wide range of skill in simulating the tropical intraseasonal variability. The total intraseasonal (2–128 day) variance of precipitation is too weak in most of the models. About half of the models have signals of convectively coupled equatorial waves, with Kelvin and MRG–EIG waves especially prominent. However, the variances are generally too weak for all wave modes except the EIG wave, and the phase speeds are generally too fast, being scaled to excessively deep equivalent depths. An interesting result isthat this scaling is consistent within a given model across modes, in that both the symmetric and antisymmetric modes scale similarly to a certain equivalent depth. Excessively deep equivalent depths suggest that these models may not have a large enough reduction in their “effective static stability” by diabatic heating.
The MJO variance approaches the observed value in only 2 of the 14 models, but is less than half of the observed value in the other 12 models. The ratio between the eastward MJO variance and the variance of its westward counterpart is too small in most of the models, which is consistent with the lack of highly coherent eastward propagation of the MJO in many models. Moreover, the MJO variance in 13 of the 14 models does not come from a pronounced spectral peak, but usually comes from part of an overreddened spectrum, which in turn is associated with too strong persistence of equatorial precipitation.The two models that arguably do best at simulating the MJO are the only ones having convective closures/triggers linked insome way to moisture convergence.
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