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Climate Predictions and the Sun

By: Dr. Ricky Rood , 6:42 PM GMT on October 05, 2008

The Sun (5): This is the last of a series on the Sun in the Earth-Sun climate system. The first four entries are linked at the end. I want to first thank both Judith Lean at the Naval Research Laboratory and David Rind of NASA for their introduction to the current literature and insights into the problem. Lean and Rind have a new paper How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006. This appears in Geophysical Research Letters. To entice you to their paper I provide the following quote from their abstract: “We find a response to solar forcing quite different from that reported in several papers published recently in this journal, and zonally averaged responses to both natural and anthropogenic forcings that differ distinctly from those indicated by the Intergovernmental Panel on Climate Change, whose conclusions depended on model simulations.” Their calculation of the solar contribution to temperature trends is 0.007 degrees C per decade. The part of the trend from the enterprise of humans (OK “manmade”) is 0.05 degrees C per decade – 7 times larger. At the end, I list a set of references with much information on the solar influence on climate change. (Some of them are quite long, so don’t click casually!)

This series of blogs was motivated by several comments on previous blogs asking for general information about solar variability and the Earth’s climate, how solar variability is incorporated into climate predictions, and questions about the current lack of sunspots. This is, at last, the one about the inclusion of solar variability in models. The short answer is that many climate models include the variability associated with the sunspot cycle. Basically, they extend the sunspot cycle that has been observed in the past decades in to the future; they use a measure of average solar irradiance variability that is characteristic of the sunspot cycle. In general, a trend in solar irradiance is not included.

If one were to look into the literature of solar variability in climate models, one does find than many of the simulations of the past century include a representation of a trend in solar irradiance. Looking at those papers that have simulated the past 2000 years, there are changes associated with the Maunder Minimum and the Medieval Warm Period. There are also a set of papers that look at the impact of similar changes in the future climate. The bottom line from these experiments is that compared with temperature changes due to increasing carbon dioxide is that both observations and model estimates of solar-induced temperature changes is small. (A good summary of this is Chapter 2 of the IPCC report linked at the end.)

The earlier blogs, I hope, clarified the point about the relative size of the solar and greenhouse contributions to the warming of the Earth’s surface. Also, it documented that the current sunspot minimum is not, as of yet, outside of our realm of experience.

These blogs also stated that our ability to model the impacts of solar variability on the Earth’s climate has significant shortcomings. Broadly, the impact that we model is weaker than the impact that we observe. These leads to the idea that we need to understand what is missing in this link … current knowledge would suggest the need to find what “amplifies” the solar signal. This is a source of uncertainty in climate change projections, but it is quantifiable, and like the solar signal itself, the uncertainty is relatively small.

In the references listed below is a comprehensive review of solar variability and its inclusion in climate models by Leslie Gray and coworkers. At the end of that document is a list of challenges for climate change modelers. Their recommendations prescribe a method for including irradiance measures, considering the variation in several spectral bands, and a better representation of solar-induced changes in ozone. They also recommend several experiments to investigate the uncertainties associated with solar variability. This is a good example of how the climate community operates.


News from NASA: Blankest Year for Sunspots in the Space Age

Some references on solar variability:

How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 by Judith Lean and David Rind. A newly published data and model paper that includes a excellent analysis of solar variability.

Living with a Variable Sun by Judith Lean. An excellent readable document for science-interested people.

The Sun and the Earth’s Climate by Joanna Haigh An online document that summarizes the state of knowledge of solar variability and the Earth’s climate.

The Influence of Solar Variability on the Earth’s Climate L. J. Gray, J. D. Haigh, and R. G. Harrison. (This is large file and document from the Hadley Center, published in 2005.)

Chapter 2 of the IPCC report A summary of the literature on solar variability in about 2005-2006, with documentation of some important changes for the previous five years. See page 188.

Blogs on the Sun.

The Sun (1)

The Sun (2)

The Sun (3)

The Sun (4)

This figure shows how solar (visible) and terrestrial (infrared) radiation flows through the atmosphere. This is an updated figure provided by Kevin Trenberth and will appear in the Bulletin of the American Meteorological Society in the article “Earth’s global energy budget,” by Kevin E. Trenberth, John T. Fasullo and Jeffrey Kiehl.

Blogs on radiative balance

Ice Water
Clouds Cool and Warm
Aerosols Cool and Warm

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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25. counters
5:05 AM GMT on October 12, 2008
Steve, I had no idea that that was how the Byrnes story ended up playing out. I always suspected it was a scam, but gee golly, who would've thought that people would take advantage of the knee-jerk actions of the skeptic community? I have no idea if "Eloise" is any different, but based on what she's written on her site thus far, I think it's a sad affair; there's no AGW to be found in this story, just a young girl and an unhealthy obsession with Al Gore.

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23. crucilandia
9:32 PM GMT on October 11, 2008
Sun’s magnetic field still in a funk during September


While the sun puts out a new and significant cycle 24 spot, the real news is just how quiet the suns magnetic field has been in the past couple of years, and remained during September 2008. From the data provided by NOAA’s Space Weather Prediction Center (SWPC) you can see just how little magnetic field activity there has been. I’ve graphed it below with the latest available data from October 6th, 2008:

click for a larger image

What I find most interesting about the Geomagnetic Average Planetary Index graph above is what happened around October 2005. Notice the sharp drop in the magnetic index and the continuance at low levels.

This looks much like a “step function” that I see on GISS surface temperature graphs when a station has been relocated to a cooler measurement environment. In the case of the sun, it appears this indicates that something abruptly “switched off” in the inner workings of the solar dynamo. Note that in the prior months, the magnetic index was ramping up a bit with more activity, then it simply dropped and stayed mostly flat.

Currently the Ap magnetic index continues at a low level, and while the “smoothed” data from SWPC is not made available for 2008, I’ve added it with a dashed blue line, and the trend appears to be going down.

However, it will be interesting to see if an uptick in the Ap index occurs, now that a significant SC24 spot has emerged. Unfortunately, we’ll have to wait until early November for SWPC to update the data set.
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22. SteveBloom
9:27 PM GMT on October 11, 2008
Re #20: What do you suppose the chances are that there's really an unassisted 14 year old behind that site? Byrnes was at least a verifiable actual person, although I suspect her effort was much more related to her father and his interest in collecting college money for her than any real interest in climate (noting how quickly she abandoned the project in favor of her new preferred field of architecture).

Re #21: And now their beautiful Maunder Minimum redux is melting before their eyes. But that's OK, they'll be happily speculating about the solar cycle 25 before long. Scientists see a star with little variability, while astrologers (at some point this goes beyond mere climate denialism) see a huge ball of pony poop.
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20. counters
1:35 PM GMT on October 11, 2008
Crucilandia, if you're going to copy verbatim a post by a different author at another site, the least you can do is link to that author's source material.

Indoctrination. LOL. The only indoctrination occurring here is the skeptics' encouraging her to seek answers to her legitimate questions from biased source acting with a clear agenda.
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18. crucilandia
9:25 PM GMT on October 10, 2008
There’s been some discussion about the “indoctrination” of AGW theory in school systems worldwide, mostly by teachers showing Al Gore’s movie, An Inconvenient Truth, in schools.

As a former school trustee in my town of Chico, CA, I can vouch for the fact that AIT has been shown in some local schools, with student discussions centered around it. It is of course not on the approved curriculum, but some teachers take it upon themselves to introduce it into the classroom on their own. Since most teachers have leeway in choosing films to show to classes, unlike with textbooks, which are chosen by the school board, films generally “fly under the radar” requiring only a form approved by the school principal.

So it was with interest that I was advised of a new website, Kids Against Anthropongenic Global Warming, put together by 14 year old girl from Far North Queensland, Australia. I see it as an antithesis to the horrible website that was put together by Australia’s ABC TV network:

TV Network Tells Kids How Long Their Carbon Footprint Should Allow Them to Live

I’ve never seen a more disgusting kid-theme for “science” education than the above link.

This Kids againts AGW site is done in the spirit of Krysten Byrnes, who wrote an essay that caught worldwide attention and then launched a website with more essays and ideas, this website is in it’s infancy. As we saw with Krysten, it takes courage to go against what is generally accepted by your peers at school. Unfortunately, she’s using a pseudonym, which is something I discourage with adults, since I think you should stand behind your words. But maybe this is the only way mum and dad would allow her to do it. Here’s a bit about her from her website:

Hi, my name’s Eloise (pseudonym) and I am a 14 year old girl from Far North Queensland, Australia. My dad first informed me that the concept of Anthropogenic Global Warming was nothing but a theory presented as fact. It really started to annoy me that people would just believe what anyone *Al Gore* says, without asking for any evidence to support what was said. My dad showed me some online links and pushed me to find a conclusion myself. My conclusion: Al Gore is a hypocrite and scaremongers people into paying him to lecture without even letting himself be challenged by skeptics, people usually want to think that man is evil and imposing on the earth and most importantly that Anthropogenic Global Warming is nothing but an unproven theory. And that is the most “Inconvenient Truth”.

Emphasis hers. Let’s give the kid some encouragement. - Anthony

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Dr. Ricky Rood's Climate Change Blog

About RickyRood

I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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