Geomagnetic Forcing of Earth’s Cloud Cover During 2000-2008?
Guest post by Roy W. Spencer, Ph. D.
I’ll admit to being a skeptic when it comes to other skeptics’ opinions on the potential effects of sunspot activity on climate. Oh, it’s all very possible I suppose, but I’ve always said I’ll start believing it when someone shows a quantitative connection between variations in global cloud cover (not temperature) and geomagnetic activity.
Maybe my skepticism is because I never took astronomy in college. Or, maybe it’s because I can’t see or feel cosmic rays. They sound kind of New Age to me. After all, I can see sunlight, and I can feel infrared radiation…but cosmic rays? Some might say, “Well, Roy, you work with satellite microwave data, and you can see or feel those either!” True, but I DO have a microwave oven in my kitchen…where’s your cosmic ray oven?
Now…where was I? Oh, yeah. So, since I’ve been working with 9 years of global reflected sunlight data from the CERES instrument flying on NASA’s Terra satellite, last night I decided to take a look at some data for myself.
The results, I will admit, are at least a little intriguing.
The following plots show detrended time series of monthly running 5-month averages of (top) CERES reflected shortwave deviations from the average seasonal cycle, and (bottom) monthly running geomagnetic Ap index values from the NOAA Space Weather Prediction Center. As I understand it, the Ap index is believed to be related to the level of cosmic ray activity reaching the Earth. (I will address the reason for detrending below).
Note that there is some similarity between the two plots. If we do a scatterplot of the data (below), we get an average linear relationship of about 0.05 W per sq. meter increase in reflected sunlight per 1 unit decrease in Ap index. This is at least qualitatively consistent with a decrease in solar activity corresponding to an increase in cloud cover.
(I’ve also shown a 2nd order polynomial fit (curved line) in the above plot for those who think they see a nonlinear relationship there.)
But just how big is this linear relationship seen in the above scatterplot? From looking at a 70-year plot of Ap data (originally from David Archibald), we see that the 11-year sunspot cycle modulates the Ap index by at least 10 units. Also, there are fairly routine variations on monthly and seasonal time scales of about 10 Ap units, too (click on image to see full-size):
When the 10 Ap unit variations are multiplied by the 0.05 scale factor, it suggests about a 0.5 W per sq. meter modulation of global reflected sunlight during the 11 year solar cycle (as well as in monthly and yearly variations of geomagnetic activity). I calculate that this is a factor of 10 greater than the change in reflected sunlight that results from the 0.1% modulation of the total solar irradiance during the solar cycle.
At face value, that would mean the geomagnetic modulation of cloudiness has about 10 times the effect on the amount of sunlight absorbed by the Earth as does the solar cycle’s direct modulation of the sun’s output. It also rivals the level of forcing due to anthropogenic greenhouse gas emissions, but with way more variability from year to year and decade to decade. (Can anyone say, “natural climate variability”?)
Now, returning to the detrending of the data. The trend relationship between CERES reflected sunlight and the Ap index is of the opposite sign to that seen above. This suggests that the trend in geomagnetic activity during 2000-2008 can not explain the trend in global reflected sunlight over the same period of time. However, the ratio of the trends is very small: +0.004 Watts per sq. meter per unit Ap index, rather than -0.045. So, one can always claim that some other natural change in cloud cover is overpowering the geomagnetic modulation of cloudiness. With all kinds of climate forcings all mingled in together, it would be reasonable to expect a certain signal to emerge more clearly during some periods, and less clearly during other periods.
I also did lag correlation plots of the data (not shown), and there is no obvious lag in the correlation relationship.
All of this, of course, assumes that the observed relationship during 2000-2008 is not just by chance. There is considerable autocorrelation in the reflected sunlight and geomagnetic data, which I have made even worse by computing monthly running 5-month averages (the correlation strengths increased with averaging time). So, there are relatively few degrees of freedom in the data collected during 2000-2008, which increases the probability of getting a spurious relationship just by chance.
All of the above was done in a few hours, so it is far from definitive. But it IS enough for me to keep an open mind on the subject of solar activity affecting climate variations. As usual, I’m just poking around in the data and trying to learn something…while also stirring up some discussion (to be enjoyed on other blogs) along the way.
UPDATE (12:30 p.m. 10 December 2009)
There is a question on how other solar indices compare to the CERES reflected sunlight measurements. The following lag correlation chart shows a few of them. I’m open to suggestions on what any of it might mean.
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Leif: What say you?
I fihd Dr. Spencer’s writings the most enjoyable and informative of the few climate scientist’s blogs I follow. A health dose of skepticism, use of scientific methods, the ability to admit his opinions are incorrect when faced with facts, and an easy down-to-earth writing style, make Dr. Spencer a great ambassador for true climate science.
“(Can anyone say, “natural climate variability”?)”
ROFL. Good one Roy. When I think of all the times that I’ve seen Gavin refer to “natural climate variability”, and I knew full well that he didn’t know what “natural climate variability” he was talking about, this all comes back as extremely funny.
To be more clear, I asked Gavin directly to identify the natural variability that was effecting temperature since 1998. He deleted my comment.
The Terra CERES and the Geomagnetic AP Indices for 2000 to date don’t look very similar to my casual eyeballing. Whereas the 1932 to date Geomag AP DOES look more compelling, at least as regards to the 1970s but rather less so for the 1998 global temp peak that is recorded elsewhere, and which if there really were a direct correlation with Geomag AP would have been a cold snap.
I look forward to Dr Spencer’s continuing work in this area, it will be interesting to see if this Cosmic Ray dog really can hunt.
I wish I could understand the math well enough to do it too.
Very cool
I’d ask Gavin to identify the cause(s) of the tree ring divergences.
The dendro Scientists have had a couple of decades to work on this issue rather than just throw up their hands and ignore the data.
I’ve posted twice on Realclimate.org asking if Gavin or Eric were interviewed regarding the editorial that ran worldwide about Copenhagen.
Twice the post was deleted.
If you’d like to see cosmic rays, build yourself a cloud chamber. This usually consists of a transparent container with supercooled alcohol vapor (cooled with dry ice). When cosmic rays go through the container the charge on the particle causes the supercooled alcohol to condense forming a track. It is like having a meteor shower in a bowl. Very cool, literally and figuratively.
Google “cloud chamber” and you’ll get lots of links on how to make one. You can do it with household materials. Try it, and I think you’ll enjoy the results.
This goes along with my “gut instinct” that it isn’t the lack of sunspots per se that cause the cooling as it is something else that happens at the same time that we see a lack of sunspots. The lack of spots being another indication or another indicator of what is going on overall and isn’t in and of itself the issue.
That a decrease in solar wind would allow more GCRs into the inner solar system seems to be quite a reasonable assumption. I would expect us to see a pulling back (deflating) of the heliopause. If the solar wind is slower then it stands to reason that the balance point between the interstellar medium and the heliosphere would shrink in size toward the sun. If the density of the wind is less, then it seems reasonable that GCRs would impact fewer solar wind particles on their way in and would arrive in greater number and with more energy.
While the change in TSI might be quite small, the change in solar wind has been quite dramatic. We keep adding up bits and pieces of evidence that decreases in solar activity change cloud cover.
So now I wonder what changes we might see on other planets. Have Venus or Saturn or Titan seen any changes over the recent years in their atmospheres? We have observation platforms there currently. What have their observations shown over the past few years? Venus is close enough for us to measure from Earth or from Earth orbit. Has there been any albedo change? While clouds on Earth are water, other planets have clouds too. I would expect these clouds to require something to form around initially. If increased GCRs result in increased cloud formation, I would not be surprised to see this in other atmospheres as well and the atmospheres that are farther out in the solar system might show a larger change.
The AP index was almost as low as it was in the ’70s in the late ’90s, but there was some kind of El Nino event in ’98. If clouds modulated SSTs, then this would be the opposite of what you would expect, wouldn’t it?
Paddy (09:34:48) :
Leif: What say you?
A R^2 of 0.323 [on smoothed data, no less] is not enough to base any conclusions on. We have good data on Ap [or similar] back to the 1840s [no typo] http://www.leif.org/research/Ap-Monthly-Averages-1844-Now.png so it comes down to finding cloud data from before 2000 and doing a better comparison.
sounds like a cool experiment, Jeff. But how do you know they are not pixie contrails?
Paddy (09:34:48) :
Leif: What say you?
If the mechanism is supposed to be via cosmic rays, the relevant correlations should be between cloud cover and the cosmic ray intensity [of which we have good data back to 1951] and not with geomagnetic activity.
And why does NASA not already have a detailed analysis of this?
Leif:
I do not trust any global cloud data before 2000. Either the geographic sampling is way too poor (which leads to MUCH larger errors than poor sampling in temperature data), or the satellites drifted through the diurnal cycle.
There is another 10+ years worth of ERBE data, though, which must be used at 72 day time resolution. That comparison should also be done.
-Roy
That is because RC is not a “conversation” in the normal sense of the word. It is a “discussion” but more along the lines of what goes on in a lecture hall and not what goes on around a table or in a lounge.
When you post it is basically like passing a note to the lecturer with your question. The lecturer can review your note and those of others and decide which ones to answer at the end of the lecture.
Postings at RC are like lectures. The communication is intended to be in mostly one direction. The entire notion of RC was to allow a certain group of people to put stuff “out there” and present it in the way they wanted it presented. In other words, the entire basic purpose of RC is to get the correct “spin” on the message.
So for you to expect a message to be actually posted that is not in line with the agenda is somewhat unreasonable unless it (their reason for posting) is so they can roundly criticize you and your question so as to prevent others from asking the same one later.
RC is not a science site. It is a “translation” site where they hope to translate their “science” so that it can be “properly” understood but people outside the academic community. And by “properly” understood I mean that it is important that people reach the conclusion they want them to reach. If your comment or question is counter to that objective, you should have no expectation of it ever seeing the light of day.
Interesting but doesn’t Svensmark propose low and thicker (therefore more reflective) clouds as agents of global cooling? I’d thought that the IR emitted by the air above such clouds that was most likely bound for deep space was a major part of his theory. I could be completely wrong, but otherwise shortwave data from CERES would only test a part of the CC via cloud theory. I should probably do some research before I spout these ill-informed guesses though; or become an elite climatologist.
Enjoy the results of supercooled alcohol? I think I just might partake of an experiment or two!
But paging Dr Svalgaard, or anyone that can recommend me a good textbook on solar science. This stuff intrigues me and I know little about it, other than a gut feeling that the Sun has a large influence on our climate. Made more interesting by having it’s own cycles and events, and emitting in a wide spectrum. Because (at least to me) it’s quite variable, it’s easy to find correlations, but would like to understand what they mean and whether they mean anything.
Given it’s current odd behaviour, it’s something I’d like to learn more about.
“And why does NASA not already have a detailed analysis of this?”
Because studies of natural climate variation do not attract funding. It takes money and right now all the money so going to AGW “verification”.
In a nutshell … it doesn’t fit the agenda so it won’t get funded.
Mars has cirrus water clouds, like Earth (compared to the other alternatives) and even snow (observed by the Phoenix lander).
Mars also followed the terrestrial warming trend with south polar dry ice sublimations.
What do we see on Mars recently? Is there an increase in cirrus cover potentially due to cosmic ray effects? Is more dry ice surviving the south polar summer?
It’s always fun to watch someone following facts.
As far as I know, no one has looked for or talked about slight changes in the sun’s angular diameter (that is, the “size” of the sun in the sky) as a way for changes to occur in the sun’s output. When scientists say that the solar irradiance does not vary enough to have a significant effect on the earth’s climate, they are talking about the apparent brightness of points on the sun’s surface — but if that surface did stay more or less the same brightness while the sun’s angular diameter increased, the sun would end up sending more solar radiation to the earth. An increase in solar output from a small increase in the sun’s angular diameter would, by the way, also explain the observed of warming on Mars (and I believe, other places in the solar system) over the last several decades at the same time the earth has been warming. The cosmic-ray cloud-formation hypothesis has nothing to say about the observed warming of other places in the solar system, and global warming skeptics would be wise to reserve some skepticism for it on those grounds alone.
Hmm. The degree of geomag disturbance may depend on the direction of the IMF. Why not try some property (density?) of the solar wind from the OMNI dataset (http://omniweb.gsfc.nasa.gov/ow.html)?
Something changed in 2003. We need to find out what the something was ASAP.
“Ulysses Reveals Global Solar Wind Plasma Output at 50-Year Low”
http://www.jpl.nasa.gov/news/news.cfm?release=2008-178
“Galactic cosmic rays carry with them radiation from other parts of our galaxy,” said Ed Smith, NASA’s Ulysses project scientist at the Jet Propulsion Laboratory in Pasadena, Calif. “With the solar wind at an all-time low, there is an excellent chance the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our solar system.”
As with CO2 AGW the GCR/cloud theory must be proved