Posts Tagged ‘Allan’

Net effect of clouds on climate is strongly cooling and not of warming

September 21, 2011

During daytime clouds shadow the earth from the sun’s radiation and have a cooling effect while at night they act as a blanket and decrease the radiation away from earth into space. For anybody who has desperately sought the shade on a warm day or has observed the absence of frost after a cloudy night, this might seem a pretty obvious and a rather trivial statement.

The alarmists’ view of global warming assumes that the net effect of clouds is to warm the earth’s climate and that it is one of the “positive feedbacks” for warming. But a new paper in September’s Meteorological Applications severely undermines these assumptions by showing that this feedback is strongly negative. To put the magnitude of this cooling effect into perspective, the net cooling effect of clouds is put at -21W/sq.m while the much-touted effect of a doubling of carbon dioxide concentration in the atmosphere is supposed to be only +1.2W/sq.m.

When this is coupled to the recent support for Svensmark’s hypothesis  on solar effects for cloud formation from the CERN cloud experiment, and the lack of warming over the last decade  while carbon dioxide has been increasing, it only emphasises that:

  1. the science of how climate varies is a long way from being settled, and
  2. the magnitude of carbon dioxide effects on climate are extremely small, and
  3. the effect of man-made emissions on the atmospheric concentration of carbon dioxide is miniscule

Whether directly by incoming radiation or indirectly by the formation of clouds or through the transport of heat by the oceans and the winds, it is the sun which is the predominant forcing. Climate models which ignore solar effects and do not have the sun at their centre are fatally flawed.

Allan, R. (2011) Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere, Meteorological Applications, 18 (3). pp. 324-333, ISSN 1469-8080, DOI: 10.1002/met.285

Abstract: Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed. 


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