Someone needs to explain the seasons to Willis Eschenbach and Stan Robertson at WUWT

I started to write this article some time ago in response to an article by Wondering Willis Eschenbach (archived here). Today there's another article on the same topic by someone called Stan Robertson (archived here) so I figured I'd resurrect this. Stan's been featured here on a previous occasion.

The main question they are asking is: why doesn't Earth heat up more when it's closest to the sun, in January? The corollary they didn't ask is, why doesn't Earth cool down more when it's furthest from the sun, in July?

The main answer is: the tilt of the earth dominates seasonal variation, not distance from the Sun. For Earth that is. (It's different on Mars.) Plus - oceans.

This is a long and long-winded article, probably with too much repetition and a tad muddled. But I've spent enough time on it so click read on if you're up for it :)

It'd be the sun, if we could only explain it...

Stan Robertson, Ph.D, P.E, has written an article for Anthony Watts' blog WUWT (archived here).  His argument starts with these points:

1. Earth has warmed over the past century.
2. The addition of greenhouse gases probably contributed a bit.
3. The sun is likely to be at least partly responsible.
4. TSI isn't enough to explain the warming of the past 50 years.

The sun warmed indirectly?

So far so good.  It's the next bit that is giving Stan a spot of bother.  His reasoning continues (my bold italics):

The sun warmed the earth indirectly not directly and the proof is that TSI variations during the solar cycle are not sufficient to explain the variations in ocean temperature over a solar cycle.

He's done some number crunching and looked up papers by scientists and concluded:

• The average amplitude of TSI reaching the earth surface in all wavelengths would be about 0.09 watt/m2 (Sou: I think, but am not sure, that Stan means this is the amplitude of change over a solar cycle).
• Ocean surface temperatures oscillate with an amplitude of about 0.04 – 0.05°C during a solar cycle -Zhou & Tung (2010).
• For each watt/m2 of increase of TSI over a solar cycle, the ocean warms by 0.085°C - Zhou & Tung (2010).
• Producing sea surface temperature variations with an amplitude of 0.04°C requires a surface heat input of 0.33 watt/m2.
• The solar TSI variations that reach the earth’s surface are smaller than the 0.33 watt/m2 needed to account for sea surface temperature variations by a factor of 3.6.

I think that what he's trying to demonstrate is that the change in solar radiation over a solar cycle cannot account for the resulting change in ocean heat over the same cycle.  He worked out that it should require 33 watt/m2 but he could only find 0.09 watt/m2.  He probably made a mistake in his assumptions or his calculations.  He did go on a bit about going below the sea surface and  I'm not sure why he did that, but it could well be the source of his error - mixing up sea surface temperature changes with sub-surface ocean heat accumulation.  I didn't follow all that he did.  Radiative forcing is not my specialty.  If you want to see what Stan did in more detail, the archived article is here.

No, Stan, it's not the sun (and he is arguing for high climate sensitivity)

Whatever, Stan jumps to hypothesising about the cause of global warming and decides that "it's still the sun", he just has to figure out how it does it.  He concludes (my bold italics):

Although the estimated 0.33 watt/m2 that is required to explain the surface temperature variations is large compared to the amplitude of TSI variations that reach the surface, it is still only about two parts per thousand of the 160 watt/m2 of solar UV/VIS/NIR that reaches the earth surface. There are many possible ways in which the sun might modulate the surface energy flux to this extent. These include modulation of cloud cover and small spectral shifts in the energetic UV that might modulate ozone absorption or produce shifts of the effective sea surface albedo. It would seem to be a fairly direct radiative effect, rather than feedback, since it must vary in phase with the solar cycle.

In summary, my calculations based on energy conservation considerations imply that the sun modulates the ocean temperatures to a much greater extent than can be provided solely by its TSI variations. The great question that desperately needs an answer is how does it do it? It should be easily understood that solar effects would not necessarily be confined to cycles. More likely, the sun has been the driver of the large changes of temperatures of the Roman and Medieval warm period, the Little Ice Age, and the recent recovery from it without requiring large changes of its own irradiance. When we understand how the sun does this, we will have begun to understand the earthly climate.

I'm not sure what Stan means by "large changes of temperature...without requiring large changes of (solar) irradiance".  But if he's trying to argue that the recent decades of global warming were caused by the sun, he's wrong.  If he does think that only small changes in solar irradiance can have a large effect on global surface temperature then he's arguing for a high climate sensitivity, which goes against all that WUWT stands for.  His argument is also lacking in that he doesn't attempt to explain why, if it's mostly the sun, TSI would not act consistently.  For example, the world has warmed in recent decades whether TSI was increasing or not.

What is causing the earth to warm

Before getting stuck into the comments, it might pay to look at all the factors that are causing the earth to warm.  There's a nifty chart in the IPCC AR5 WG1 Technical Summary (page TS-91) showing all the components of radiative forcing from 1750 to 2011.  It's a bit small so I suggest you click the chart to enlarge it:

Source: IPCC AR5 WG1 Technical Summary

Fig TS.7: Radiative forcing of climate change during the industrial era shown by emitted components from 1750 to 2011. The horizontal bars indicate the overall uncertainty, while the vertical bars are for the individual components (vertical bar lengths proportional to the relative uncertainty, with a total length equal to the bar width for a ±50% uncertainty). Best estimates for the totals and individual components (from left to right) of the response are given in the right column. Values are RF except for the ERF of aerosol-cloud interactions (ERFaci). An additional rapid adjustment to aerosol-radiation interactions of –0.1 [–0.3 to +0.1] W m–2 is attributable primarily to black carbon (ERFari-RFari in Figure TS.6). CFCs= Chlorofluorocarbons, HCFCs= Hydrochlorofluorocarbons, HFCs=Hydrofluorocarbons, PFCs= Perfluorocarbons, NMVOC= Non-Methane Volatile Organic Compounds, BC= Black Carbon. {Figure 8.17}

From the WUWT comments

Solar scientist Leif Svalgaard has had a lot to say in the comments and, I think, has been enjoying himself.

lsvalgaard quotes Stan Robertson and says:

October 10, 2013 at 3:03 pm

The solar TSI variations that reach the earth’s surface are smaller than the 0.33 watt/m2 needed to account for sea surface temperature variations by a factor of 3.6 for this smallest estimate of sea surface temperature variability.

So, in normal science, that falsifies the assumption that solar variations are the cause.

lsvalgaard says:

October 10, 2013 at 3:23 pm
Hockey Schtick says: October 10, 2013 at 3:16 pm - For a start, here’s 50 papers describing potential solar amplification mechanisms

None of those explain how 3.6 times more heat reach the surface than the variation of what the Sun puts out…Otherwise the climate system would be a nifty energy producer: you put 10 units in and you get 36 out. I want one of those :-)

 lsvalgaard says:

October 10, 2013 at 4:01 pm
milodonharlani says: October 10, 2013 at 3:52 pm Science has historically been full of surprises & strongly-held certainties frequently overthrown by better analysis & discovery of more information.

I’m not discussing this in general [and this is all the other people trotting out their usual stuff], but let us stick to the article if this thread: it claims that 0.33 W/m2 input is required and notes that TSI only provides 3.6 times as little, or 0.09 W/m2. How can that work? what discovery awaits us that can provide 3.6 times more energy than supplied by the variation of TSI? The Sun cannot, the deep ocean might, or the calculation is wrong.

David Archibald says the heat is invisible, it's hiding, it's already there but our thermometers can't measure it:

October 10, 2013 at 4:10 pm
What if the heat is already there? Then it doesn’t have to diffuse. Cloud cover varies over the solar cycle. The oceans have an albedo of 5% so most visible light gets through and can get as far as 200 metres down.

Jim G says, it's humans running around releasing energy got from nowhere at all (not the sun), maybe jogging and doing push-ups and tossing all the released energy into the oceans (excerpt) :

October 10, 2013 at 4:13 pm
...How can the trace gas (0.039% of atmosphere) CO2 be the recognized cause of global warming while all of the energy released by human activities be ignored as a source of heat. The human race is one big UHI in some respects. More wars and a major plague would fix the problem. Just think how plants and wildlife would flourish without us pesky humans. Oh, wait. Who would plant the trees after forest fires, no fish and game department to help keep a wildlife balance, no more protection of endangered species from predation like sage grouse and raptors….never mind.

geran says the sum is bigger than the total!:

October 10, 2013 at 4:34 pm
And, once again, we cannot forget (exclude) all of the “products” supplied by our Sun. TSI is only one in the basket.

lsvalgaard says:

October 10, 2013 at 4:35 pm
Joe says: October 10, 2013 at 4:27 pm Because the measurements are at different places. TSI is measured at the top of the atmosphere, the energy “entering” the climate system is (essentially) at the bottom of it.

The article says explicitly: “Thus the average amplitude of TSI reaching the earth surface in all wavelengths would be about 0.09 watt/m2″ so is at the ‘bottom’

stuart L says:

October 10, 2013 at 4:53 pmWell how come CO2 is supposed to warm our planet, when it does not add even as much as 0.09wm/m2 to the budget

About Stan Robertson, Ph.D, P.E

Stan apparently retired in 2004 after teaching physics at Southwestern Oklahoma State University for 14 years and before he had a chance to learn about atmospheric physics. In addition to teaching at three other universities over the years, he has maintained a consulting engineering practice for 30 years.  All this makes him eminently qualified to write a blog article about climate for Anthony.  (If he'd studied and taught climate science or any related discipline, he'd never get a guernsey at WUWT.)