The Solar Irradiance Issue

Related to the assorted phenomena pertaining to solar cycles, including spot frequency, spotless days, solar wind intensity etc., is the solar irradiance. This is just the solar radiance - in watts per square meter per steradian - integrated over the full solar disk.

"Steradian" denotes a solid angle measure. See, e.g. the definitional details (with diagrams) here:

http://en.wikipedia.org/wiki/Steradian

Needless to say, irradiance has a direct bearing on the issue of climate change and to what degree the Sun is responsible, and especially whether (quantitatively) its irradiance over any one solar cycle or period therein overrides the human-incepted, CO2 -driven, greenhouse effect.

In his lecture at the 40th Meeting of the Solar Physics Division of the American Astronomical Society ('Solar Irradiance: Recent Results and Future Research Plans') Thomas N. Woods of the University of Colorado dealt with the matter as it pertains to the current cycle, and in particular some recent measurements.

Woods began by noting the assorted recent periods wherein irradiance measurably varied, including: the Medieval maximum, the Sporer minimum (1400s), the Maunder minimum (1600s), the Dalton minimum (1800s). He noted with emphasis that there is no single uniform value to characterize a time interval or period, since the radiance itself can vary hugely on small or local scales. For example, solar flares can propel radiance increases 50 times over normal and thereby affect the irradiance.

On average though, with such violent inputs smoothed out, the Earth's temperature changes by about 0.07 K (kelvin) over a solar cycle. Compare this to the 0.6 K change (increase) in global temperatures over the past 100 years arising from human-caused greenhouse effect. Thus, the human component is over 8.5 times greater.

Even if the solar forcing on climate is enhanced by positive feedbacks the amplification is usually no more than a factor 2. So that 0.07 K increases become 0.14 K increases. The human component is still more important by a factor 4.2, a point made by Woods when he emphasized that the recent results support the hypothesis that anthropogenic greenhouse gases are the primary contributor. This despite all the politicos, think tanks and yahoos who keep blabbering that climate change arises from "natural cycles" - meaning the Sun is responsible.

The results, numbers simply don't support that and one hopes (eventually) my fellow Mensans and Ilians will finally get that into their libertarian -compromised noggins. (See my earlier blog entry about the effects of agnotology- and the deliberate sowing of doubt by powerful interests, usually economic or political.)

In his envisaging of future results, research, Prof. Woods echoed a plaintive cry I've often made: that for really solid and unimpeachable irradiance quantification we need to be able to detect and record the real total luminosity change from minimum to minimum. Again, one sees money as a core issue and one hopes Obama will make it available soon for more solar work, observation. Especially for cycle 24.

Other questions we need to have addressed to sleep better at night include: 1) How exactly are changes in the solar magnetic field related to irradiance, 2) What specific end-to -end calibrations are needed to obtain the total solar irradiance per cycle?, 3) How can we account for a nearly 8% difference in irradiance as compared to measurements made in the near infrared?

All of these answers are those which inquiring minds want to know. Hopefully before the next solar cycle (25) commences!