Albedo effect

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

Since feedbacks may have a large potential for control of albedo and therefore temperature, it seems necessary to highlight them as targets for study and research. Besides the simple example above of cloud area or cloud extent, there are others that can be identified. High-altitude ice clouds, for example, (cirrus) have both an albedo effect and a greenhouse effect. Their occurrence is very sensitive to the amount of water vapor in the upper troposphere and to the thermal structure of the atmosphere. There may also be missing feedbacks. 

The computation results by Kashiwagi et al. (2000) are shown in Fig. 4.11 and Fig. 4.12. This model calculation cannot explain the decrease of temperature since the middle Miocene (ca. 14 Ma) to present. Kashiwagi et al. (2000) calculated the effect of albedo by ice sheets to explain this inconsistency. However, the albedo effect is less than 1 °C, suggesting that this effect is not important. 

Body Radius (km) Surface pressure (bar) Albedo Effective temperature (K) Surface temperature (K) Surface g (m s-2)... 

The climatic system involves numerous factors that intensify climatic changes with minimum forcings. The withering or death of plants, for example, may cause a decrease in evapotranspiration and hence lead to precipitation attenuation, which may further increase drought conditions. In cold-climate regions snow cover formation is accompanied by a strong increase in albedo, which favors further cooling (the so-called albedo effect ). Substantial climatic feedbacks are associated with the dynamics of thermohaline circulation. 

Pearl J. C. and Conrath B. J. (1991) The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data. J. Geophys. Res. 96, 18921 -18930. 

The most important greenhouse gas at present is not carbon dioxide but water vapour, simply because there is so much of it in the atmosphere (Box 6.1). Volcanoes emit large amounts of water vapour (c. 1 Ttyr-1 Skelton et al. 2003), but even so this flux is minor compared to evaporation from the oceans and evapotranspiration from plants (c.0.25% see Fig. 3.12). In a warmer world, such as during the Cretaceous, the atmosphere can hold more water vapour. However, the extent of the warming caused by extra atmospheric water vapour is difficult to predict because clouds also exhibit an albedo effect, and the balance between the greenhouse and albedo effects varies with cloud type and altitude (Lovelock Whitfield 1982). 

Boucher, O., and Lohmann, U. (1995) The sulfate-CCN-cloud albedo effect, Tellus 47B, 281-300. Charlson, R. J., Langner, J., Rodhe, H., Leovy, C. B., and Warren, S. G. (1991) Perturbation of the northern hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols,... 

Boucher, O., and Lohmann, U. (1995) The sulfate-CCN-cloud albedo effect, Tellus, 47B, 281-300. 

The photolysis rate constants calculated by Eq. (3.29) and actually measured values for example for NO2 are sometimes agree well and sometimes have large discrepancy (Kraus and Hofzumahaus 1998). Particularly in the case of the photolysis rate above cloud, in cloud and above snow the discrepancy between the calculated and observed values are large. It is discussed that there are uncertainties in the treatments of albedo effects (Van Weele and Duynkerke 1993 Junkermann 1994 Wild et al. 2000 Lee-Taylor and Madronich 2002 Simpson et al. 2002 Brasseur et al. 2002 Thiel et al. 2008). 

The albedo, effective temperature, and energy balance of Uranus was investigated by Pearl et al. (1990) using Voyager 2 data. They found an effective temperature of 59.1 0.3 K. Due to the low temperatures of Uranus useful measurements were derived from the infrared spectra only between 180 and 400 cm. Pearl et al. (1990) give a detailed description of the extrapolation procedure used to obtain the spectral information below 180 cm. ... 

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