This is the first post in a series examining the sun-sunspot-climate connection
The skeptics are squawking again, their blogs achatter with talk about solar variability and sunspots. According to them, anybody who is anybody in climate science now knows the sun is to blame for global warming. Even the New York Times recently wrote about the low level of solar activity this year and the possibility of a coming ice age. Can any of this be true?
Of course the sun affects climate and there is little doubt that variations in the sun's energy (called the total solar irradiance or TSI) have caused significant climate swings in the past. For example, the so-called Little Ice Age, an anomalously cold period that peaked in the 1600s, may have been caused by an extended interval with low TSI (see here).
But just because changes in TSI have caused climate variations in the past does not mean they are the cause of global warming today. If variations in TSI were responsible for the increased global temperatures of the past few decades, then there would be a corresponding increase in TSI itself. Has there been? We can answer this question in a very straightforward way - not with models or theories but with actual data.
Since 1978 we have monitored the TSI using a series of instruments mounted on satellites. To determine if there has been a net change in TSI over this 30-year period, one must "stitch" the data from each of these instruments into a single, composite record. (I should note a complicating factor here: a gap between 1989 and 1991 with no measurements at all.)
To date, two such composites have been produced: one by scientists at the Physicalisch-Meteorologishes Observatorium Davos (PMOD) and the other by scientists involved with one of the TSI-measuring instruments, the Active Cavity Radiometer Radiance Monitor (ACRIM). Each used a different method to bridge the data gap and each produced slightly different results.
The composite from the ACRIM group is shown here. Most apparent is the cyclic pattern in TSI with maxima and minima occurring approximately every 11 years. This is the so-called 11-year sunspot cycle - which will be the subject of the second post in this 3-part series.
There can be little question that the ups and downs in TSI over any given cycle do affect our climate. But these ups and downs are relatively small -- only about 0.3 percent, causing perhaps a 0.15 degree Fahrenheit swing in global temperatures from solar minimum to solar maximum (see how solar variability affected 2007's temperatures). By comparison, the net rise in global temperatures since the Industrial Revolution has been just under 1.5 degrees Fahrenheit, ten times that amount.
But to understand the role of TSI in global warming, we must look at the long-term average -- that is, not the variations within an 11-year solar cycle but the net variations over multiple cycles. As the graphic here indicates, the ACRIM composite finds that over the past three solar cycles, TSI has increased about 0.004 percent per decade. It's an increase but a tiny one -- much smaller than the variations in TSI from peak to valley in any given solar cycle and far too minuscule to explain the warming seen in the last 30 years. By comparison, the PMOD composite finds a net decrease in TSI by about 0.012 percent per decade.
Some discussions out there make much ado over the differences between the ACRIM and PMOD composites. But for the purposes of this discussion, the differences are moot and the conclusions the same. The ACRIM web site puts its well: "Both time series demonstrate no significant trend over the two decade period separating the first and third solar activity minima." In other words, one can not attribute the lion's share of global warming in the last 30 years to changes in the sun's energy output. This conclusion is not based on a model or solar theory; it is based on the facts - data pure and simple.
In the next post in this series, we turn our attention to sunspots.
Global Warming and Predictions of an Impending Ice Age Part 2: Sunspots
Global Warming and Predictions of an Impending Ice Age Part 3:
Global Warming Since 1998?
Dr. Bill Chameides is a member of the National Academy of Sciences and the dean of the Nicholas School of the Environment at Duke University. He blogs regularly at www.thegreengrok.com.
Follow Bill Chameides on Twitter: www.twitter.com/theGreenGrok
I'm thinking that if the science was so strong those two approaches wouldn't be necessary.
Bill, I am certain you know 100x what I know about the environment, so surely you would be able to capture the best of the skeptics arguments rather than the most feeble. Sure, some skeptics articulate their argument exactly as you describe.
Perhaps you feel that posts like the above are going to pull your reader's opinions towards what you are sure is the important and accurate point of view - that CO2 is the cause of the last 100 years of warming.
But every time a knowledgeable & scientific commentator characterizes all skeptics as unable to comprehend what can clearly be laid in 3 simple paragraphs and a graph - I think to myself, "is this knowledgeable scientist unable to understand the skeptics arguments? - therefore maybe he's not that smart - or is the science really not that compelling and the only recourse for those who believe CO2 is a clear and present danger is to ridicule and attack skeptics?"
If what I have said does make some sense, then I look forward to being able to read the essence of an informed skeptics position with discussion of why it's poor.
Human activity causing environmental damage, absolutely! BUT I remember when ICE AGE COMMING! was being touted by many in the 70s and 80s.
When I look a the earth surface temperature charts spanning the past 450K years, I am satisfied as to what the principal cause is and what the contributing causes may be.
All that being said, scientists will still look at the possibility of natural cycles, in secret like Galileo during the dark ages.
To those who still have an open mind, but fear being burnt at the stake for speaking out, keep up the healthy curiosity!
I will now slip on my asbestos underware.
1. With regard to the "ICE AGE IS COMING" -- it's a red herring. Take a look at my post on the subject (http://www.nicholas.duke.edu/nicholas/insider/thegreengrok/cooling).
2. With regard to long-term climate change. Sure, these climate changes occurred and sure, they were caused by solar and other natural causes. However, it is a logical fallacy to conclude that because past climate change was natural, the present climate change must be. Physics still applies, and a source of heat for the current warming is required.
3. I do not have the impression that scientists are looking at the possibility of natural cycles "in secret like Galileo during the dark ages." On the contrary, take a look at the scientific literature -- it is filled with papers on the subject. How do you think we got the data I presented on solar radiation? It was because scientists launched instrumented satellites to monitor the Sun in large part to determine its role in global warming.
But, let's assume for the sake of argument that there is significant uncertainty. Doesn't that make our situation analogous to driving on an unfamiliar road at night in the fog? The road ahead might be clear, or it may not. There may be a cliff ahead that we won't see until it is too late, with fatal consequences.
In such a situation it does not make any sense to just keep driving on at full speed (accelerating actually, since out CO2 output continues to increase). The smart thing to do in that situation is to exercise some caution and slow down.
http://scienceandpublicpolicy.org/sppi_reprint_series/solar_changes_and_the_climate_ar4_analysis_series.html
Over 100 years, D'Ale, et al, found good relationship between TSI and running mean US Temperature, r-squared of 0.59.
1. As stated many times, I agree that solar variations lead to climate changes.
2. My focus is the last 30 years, the period, and the only period, for which we have direct, space-borne measurements of TSI. There is some intra-cycle correlation between global temperatures and TSI but no significant inter-cycle correlation.
I just want to see more comparisons:
TSI vs Arctic temperature, sea leave (if you have?)
Also, waiting for solar winds and cosmic rays comparision.
Thank you for the TRUE data :)
Cosmic rays have been demonstrated to increase cloud formation. With increased sun activity and fewer cosmic rays (recent past) the earth warms due to fewer clouds, but with less solar wind (now) and more cosmic rays, more clouds form and the earth cools. Thus far as none of the computer models address cloud formation; the topic is considered too complex. I find this troubling as it is a self-evident fact that a cloudy day is cooler than a sunny day, but somehow this fact is not explored.
I find it unsettling that major topics such as the linkage between solar winds/cosmic rays/cloud formation are not more thoroughly explored, while much more minor issues such as CO2 receive massive media coverage. Anyone with a computer can look up the solar activity on a daily or historical basis and plot up some sun-spot numbers against temperature data. No need for Cray supercomputers, as the latin saying goes "Nullius verba" (don't take my word for it; look for yourself).
1. You object to my tone. Point well taken. I apologize.
2. With regard to topics and topics not covered. I am not sure the criticism is warranted. As I stated in the piece, this particular post was specifically on the influence of TSI on global temperatures and the subject of sunspots and cosmic rays will be covered in my next post in the series. But don't take my word for it...
I would suggest you buy a dvd by Henrik Svensmark, a Danish scientist who has done much study on cosmic radiation. It is a very good video. Basically, less sunspots mean less shielding from cosmic radiation, more ionization in our atmosphere, more clouds, greater cooling.
Here is more reading:
http://www.dailytech.com/Sun+Makes+History+First+Spotless+Month+in+a+Century/article12823.htm
http://www.dailytech.com/Solar+Activity+Diminishes+Researchers+Predict+Another+Ice+Age/article10630.htm
And NASA. The solar wind has decreased by 20% in the past 10 years.
http://science.nasa.gov/headlines/y2008/23sep_solarwind.htm
1. Actually, I "start(ed) out talking about sunspots" AND solar output in the introduction. I also started out by saying that this first piece in a series on the subject would be on solar output or TSI. If you had bothered to read the post to the end, you would have seen that I plan to cover sunspots in the next part of the series.
2. Thanks for the video suggestions, but I am well aware of the hypothesized connection between sunspots, cosmic rays, and climate. The hypothesis has been around for some 30 years. Tune in to the next post in this series for a discussion of that connection. Your comments on that one will be welcome of course, but you could actually read the post before commenting.
However, Bill also neglected to show that there is a La Nina event at EVERY solar minimum. A La Nina event is when the surface of the Pacific Ocean becomes cooler than normal.
So Bill, if you want to explain the connection between solar irradiance and Earth temperatures, do so with integrity. Don't try to cozen us with selective data.
Is ther global warming or global cooling. Using such a small period of time and questionable accuracy, I really don't know. In the worst case scenarios in both cases, our society of today will be drastically effected. I remember Joe Friday's great phrase: "Just the facts please."
Is the sun the source of that extra heat? The data clearly show that it is not. In response to Joe Friday -- those are the "facts." Does that mean that the sun has not changed in the past? Does that mean that those changes have not caused major climate fluctuations? No on both counts. But that is not relevant to the issue addressed in this post.
All of this addresses the cause(s) of warming in the past few decades. It does not address the future trajectory of the climate. I'll cover that in another post in this series, so stay tuned.
1. I never said or implied that there was not an "unequivocal connection between solar activity and Earth temperature changes." Here is what I did say:
" Of course the sun affects climate and there is little doubt that variations in the sun's energy (called the total solar irradiance or TSI) have caused significant climate swings in the past. For example, the so-called Little Ice Age, an anomalously cold period that peaked in the 1600s, may have been caused by an extended interval with low TSI (see here)."
I am not sure how I could be more explicit than that. And, by the way, I agree that the rebound from the Little Ice Age was most likely caused by an increase in solar activity following the Maunder Minimum (http://astrophysics.suite101.com/article.cfm/maunder_minimum_variable_sun).
I'll make a couple other points in separate responses ....
And I did not say you did. I said, "Bill would need to provide sunspot data for the past 300 years, not 30 years..." and then it was my opinion that you would see the unequivocal connection between solar activity and Earth temperature changes.
Because the Earth has polar ice, it has a mechanism for storing heat without significantly raising the atmospheric temperature. Increases in solar irradiance accrue, however, the heat manifests as ice changing to water thus decreasing the Earth's albedo. Fast heating of the Earth from 150 years ago is absorbed by the ice with very little atmospheric temperature change, but when the ice is significantly reduced, the Earth is able to absorb more solar irradiance in the visible spectrum. Hence, temperatures may continue to rise slightly even if total solar irradiance decreases slightly or remains constant.
As Bubu pointed out above, changes in solar irradiance also relate to changes in cosmic rays hitting the Earth, which affects cloud cover. There are several feedback systems related to solar activity.
If carbon dioxide were the true cause of global warming, then a linear increase in temperature would occur. Let us predict the warming or cooling of the coming winter (December 2008 through April 2009). Then we can falsify either the global warming theory or the TSI theory.