Blog Letter from Bob Foster

Date: Tue, 22 Mar 2005 16:20:11 +1100
From: “Bob Foster” <fosbob@bigpond.com>
Subject: Dimming & sunspots

Dear All,

My wife watched the “Global Dimming” program on ABC (government-funded) TV
last night, and said the second half was pure catastrophism.  We will be subjected to a ‘double whammy’ of human-caused global warming about 2030. You can guess the rest.

Interestingly, there are two related things that Australian climate scientists appear notably incurious about.  Perhaps as a result, the word “sunspots” didn’t make it on to the program - or at least, she didn’t hear it mentioned.

** Current brightening/dimming appears to be very largely solar-controlled. Any discernible contemporary human influence on B/D at the global scale would have to be of secondary importance.

The reference with the data (not the conclusions) is: E. Palle et al 2004, “Changes in Earth’s reflectance over the past two decades”, Science v. 304, pp. 1299-1301. This crucial paper has already been discussed by our group.

Satellites show that during the last completed sunspot cycle, cloudiness and reflectance (albedo) decreased, and hence more of the Sun’s little-varying irradiance reached Earth’s surface - increasing estimated forcing between 1985-97 by a whopping 10 W/sq m.

(Scale is provided by comparison with human-caused greenhouse warming. IPCC says GHGs have provided increased forcing of 2.4 W/sq m since the start of the Industrial Revolution at 1750.  It also says that increased insolation changes resulting from solar variability have provided only a minuscule 0.3 W/sq m of extra forcing since that time.)

The sun reverses magnetic polarity after each (Schwabe) sunspot cycle to complete the (Hale) double cycle - which appears to be a crucial modulator of natural  warming/cooling at the decadal time-scale.  Between 1997 and 2003 brightening has been replaced by dimming, and as a consequence solar forcing has decreased by about 6 W/m sq.  The “Dimming” program didn’t make the connection.

It will be interesting to see what happens after the end of the current cycle at sometime about 2006.  Will there be another reversal, and the return of brightening?

** South Africa has enjoyed, like Australia, a slight upward trend in rainfall over the past 100 years.  Like Australia, rain is not uniformly distributed over the individual years comprising the century.  Instead it comes as droughts and floods.

Here, the reference is: Will Alexander 2005, “Linkages between solar activity and climatic responses”, Energy & Environment v. 16 no. 2 (in press). I don’t know when 16/2 comes out (16/1 has already reached Australia), but it should be worth waiting for.

In S. Africa, Alexander finds that one sunspot cycle has a small flood followed by a big drought, and the next cycle has a big flood followed by a small drought.  The overall pattern encompasses two sunspot cycles – as might be the case for B/D variability.

Could there be a similar Sun/climate relationship in rainfall at about the same latitude in SW and/or SE Australia?  Does anyone here want to know?

Judging by last night’s TV program, it is time mainstream climatology began to take the sunspot cycle, and particularly the double (Hale) version, a little more seriously.  After all, remember, these scientists have but one objective - the advancement of scientific understanding in their field. Just like us.

Regards, Bob Foster