Water Vapour Feedback .

By steven d keeler | Apr 08, 2014

 

Box 8.1 of 4AR Chapter 8 page 632 states:

The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration, so it is the fractional change in water vapour concentration, not the absolute change, that governs its strength as a feedback mechanism. Calculations with GCMs suggest that water vapour remains at an approximately constant fraction of its saturated value (close to unchanged relative humidity (RH)) under global-scale warming (see Section 8.6.3.1). Under such a response, for uniform warming, the largest fractional change in water vapour, and thus the largest contribution to the feedback, occurs in the upper troposphere.

Now, fast forward to WG1AR5 - IPCC

Chapter 9 Page 763

The limited number of studies available for the CMIP5 model ensemble broadly confirms the results from the earlier model generation. In tropical regions, the models are too dry in the lower troposphere and too moist in the upper troposphere, whereas in the extratropics they are too moist throughout the troposphere.  However, many of the model values lie within the observational uncertainties.

Page 825

The estimated fingerprint for some variables such as water vapor is governed by basic physical process es that are well represented in models and are rather insensitive to model uncertainties. Figure 9.44 illustrates slight improvements in the representation of some of the modes of variability and climate phenomena discussed in Sections 9.5.2 and 9.5.3, suggesting with medium confidence that models now better reproduce internal variability.

Page 771

Another possible source of model error is the poor representation of water vapour in the upper atmosphere (Section 9.4.1.2). It has been suggested that a reduction in stratospheric water vapour after 2000 caused a reduction in downward longwave radiation and hence a surface-cooling contribution, possibly missed by the models, However, this effect is assessed here to be small, because there was a recovery in stratospheric water vapour after 2005 (Section 2.2.2.1).

Chapter 2  Page 161 refers to 2.2.2.1

Because of large variability and relatively short data records, confidence in stratospheric H2O vapour trends is low. Near-global satellite measurements of stratospheric water vapour show substantial variability but small net changes for 1992–2011 .

 

And the amplification factor of water vapour on feedback has been the single most argued cause resulting in catastrophic human caused global warming !

These are the sorts of "things" that the crowd of warmists DO NOT want to discuss, DO NOT want you to read, know of and then consider.

Why do you suppose this information is buried in Chapters of the document, ( AR5 ) spread out so as to make linkage and conclusion based upon following the entire thread, almost impossible for the layman to follow ?

 

Climate Change 2013: The Physical Science Basis

Box 8.1 of 4AR Chapter 8 page 632 states:

The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration, so it is the fractional change in water vapour concentration, not the absolute change, that governs its strength as a feedback mechanism. Calculations with GCMs suggest that water vapour remains at an approximately constant fraction of its saturated value (close to unchanged relative humidity (RH)) under global-scale warming (see Section 8.6.3.1). Under such a response, for uniform warming, the largest fractional change in water vapour, and thus the largest contribution to the feedback, occurs in the upper troposphere.

- See more at: http://www.friendsofscience.org/index.php?id=710#sthash.Dopkv8oY.dpuf

Box 8.1 of 4AR Chapter 8 page 632 states:

The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration, so it is the fractional change in water vapour concentration, not the absolute change, that governs its strength as a feedback mechanism. Calculations with GCMs suggest that water vapour remains at an approximately constant fraction of its saturated value (close to unchanged relative humidity (RH)) under global-scale warming (see Section 8.6.3.1). Under such a response, for uniform warming, the largest fractional change in water vapour, and thus the largest contribution to the feedback, occurs in the upper troposphere.

- See more at: http://www.friendsofscience.org/index.php?id=710#sthash.Dopkv8oY.dpuf

 

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