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Saturday, October 3, 2015

Notes on Obliquity

It is usual, when discussing Milankovitch cycles, to dismiss any effect of obliquity on global, annual mean insolation based on the fact that the Earth is a sphere.  I did it myself in a comment on Skeptical Science.  As the Earth is an oblate spheroid, however, it is not strictly accurate.  In particular, on the equinoxes, the Earth presents its minimum aspect to the Sun, showing an eclipsed area of 1.2737 x 1014 m2 to the Sun.  As the Earth moves to the solstice (either winter or summer) it presents its maximum aspect, showing an eclipsed area of 1.2744 x 1014 m2.  That represents a difference of 0.05% in recieved sunlight, or approximately 0.12 W/m2.  That seasonal variation is much less than the 6.8% (16.2 W/m2) seasonal variation due to the eccentricity of the Earth's orbit.

Saturday, September 19, 2015

New Blog

Just a small notice of my new blog, which will be of a more personal nature than By Brisbane Waters.  I am also using it to discuss important issues not related to climate change.

Friday, May 29, 2015

Monday, May 25, 2015

Grantham and the media

I haven't written a post on the Queensland 2011 floods for a while.  It is, however, back in the news due to issues relating to events at Grantham.  I have very little to say about that in particular.  Those issues turn on detailed matters of topography and hydrology on which neither I, nor the residents of Grantham have the necessary knowledge to have an informed opinion.  The residents of Grantham do, of course, have the relevant expertise on what they saw; and what they saw must inform any hydrological assessment of the effects of the flood on Grantham.  Knowing what you saw, and interpreting its significance, however, are not the same thing.  Therefore the claims of the Grantham residents do not determine what happened in 2011, and should not by themselves determine the results of the current inquiry.

The task of the inquiry is being made harder by bad reporting on the floods.  I discuss below the fold one such example of bad reporting by Channel Nine, echoed by the Sydney Morning Herald.  Once again I have copied a comment from SkS for convenience, and in this case the first part of the comment is not directly relevant to the issue of bad reporting by media.  I have retained it, however, as it does give useful background on the general situation in the Lockyer Valley at the time of the Grantham flood of Jan 10, 2011.