Global Warming and Predictions of an Impending Ice Age - Part 1
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?
Part 1: Solar Variations
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.
Examining the Data to See How Much Solar Variations Affect Climate
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.
Solar Variations: Too Tiny to Matter
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
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One of the influences in making me a skeptic of AGW or CO2 induced global warming has been the characterization of skeptics as a) somewhat evil ("deniers", oil company employees, etc) and b) somewhat stupid, unable to see the blindingly obvious.
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.
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stevecarsonr - I agree that ad hominem attacks are out of bounds. If I am guilty of such attacks, please point them out. Specifically, I don't think I said or even implied that anyone was "unable to comprehend" anything. All I did was present the data. And by the way, you might take a look at the comments of "fumes" below. Do those fall into the category that you find troubling?
Look, I am in agreement on most anything we can do to clean up the environment. But whenever healthy dissent or questions on a scientific issue results in ridicule or worse, I will only look closer at other posibilities.
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.
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open_mind - Good that you have an open mind. Let me make a couple of points:
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.
I don't believe there is much uncertainty that global warming is real. The skeptics come up with lots of claims that there is uncertainty, but on closer inspection these are always wildly exaggerated, lack supporting evidence, or just completely made up.
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.
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BlackbirdHighway - Makes sense to me. More on that in my fourth and final post in this series.
Here is a more comprehensive study for longer time period:
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.
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JBridge: There are a number of reasons why I don't find the studies you quote compelling, but it is all irrelevant.
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.
Thank you Bill,
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 :)
Firstly, I object to your tone in this article regarding people who disagree with you. Science cares not one whit for your personal "squawks", or mine, or of any of 30,000 scientists that may fall on one side or the other of this topic. Secondly, the issue surrounding the sun's activity, or lack thereof has nothing to do with TSI, so your focus on that issue is irrelevant. The issue is the interaction between solar winds and cosmic rays.
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).
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Shoshin:
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...
nullius in verba, but don't take my word for it! say shoshin, thanks for including the clouds. you can add precip to that equation too. evil co2 can't by itself do squat (e.g.~ cold desert nights!) but with the help of water vapor can do a lot: warming at first by trapping heat leaving the earth (so called greenhouse thingy) but then as you rightly point out, cooling by preventing warming in the first place. have you read any clausius and clapeyron?
You start out talking about sunspots, then quickly change to TSI. Two completely different animals. TSI or total solar irradiance is the spectrum from visible up through the IR. It has been measure by satellite since about 1979. Sunspots though, create magnetic fields which shield out solar system from cosmic particle radiation.
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
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bubu. thanx for the comments. here's the response.
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.
Bill makes a common error while presenting the case for solar warming. The present warming cycle of the Earth began over 150 years ago. Bill would need to provide sunspot data for the past 300 years, not 30 years, in order to see the unequivocal connection between solar activity and Earth temperature changes.
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.
I agree with you in that if you want to chart the weather system, twenty years to far too short of a time. In the past 1,000 years we have gone through small ice ages and eras of warmer temperature. For an excellent example, check out what happened to the Viking colonies in Greenland.
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."
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Semaj51: Climate changes on a variety of scales. Changes on 1,000-year time scales are certainly interesting but are not necessarily relevant to climate change that is occurring on decadal time scales. As regards the immediate future and the well-being of my children and grandchildren (yours as well?), climate change on decadal time scales is of primary concern. We can all agree that the temperatures have increased in the recent past with corresponding disruptions of the climate. That begs the question, why. And the answer to that question MUST involve an extra source of heat -- that's just basic thermodynamics.
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.
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volantis - Thank you for your comment, but I don't think I made an error, common or otherwise, and I would never dream of cozening.
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 ....
"1. I never said or implied that there was not an 'unequivocal connection between solar activity and Earth temperature changes.' "
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.
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2. The issue addressed in my post, and most relevant to concerns about climate change, is the cause of the warming -- indeed the accelerated warming -- that has occurred over the past 30 years.
The most basic law of physics -- the First Law of Thermodynamics -- requires that there must have been an extra source of heat to cause this warming. And while an increase in solar output may have been the driver of warming in 1800s and part of the 1900s, it was clearly not the cause of the warming in the later part of the 20th century. Why? Take a look at the graphic of TSI from the post -- no net increase in the heat from the sun. (The possibility that sunspots may have been responsible will be addressed in my next post in this series.)
''The most basic law of physics -- the First Law of Thermodynamics -- requires that there must have been an extra source of heat to cause this warming.'' ~ OR ~ an extra lack of heat sink. you know heat sink bill, suddenly your eggs are done?
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3. Finally ... the El Nino/La Nina argument is a red herring. El Nino events tend to release heat from the ocean to the atmosphere; La Nina events do the opposite. The possibility that there may be a causal relationship between the El Nino/La Nina oscillation and the solar cycle is interesting but still speculative (see http://www.agu.org/pubs/crossref/2008/2008GL034831.shtml).
But even if it is true, it does not change the basic conclusion of my post. Yes, global temperatures tend to cycle up and down with El Ninos and La Ninas, just as they do with the maxima and minima in the solar cycle. But for the purposes of understanding global warming, we are interested in the long-term change in temperature over multiple cycles, not the intra-variability within a single cycle. For the El Nino/La Nina oscillation to lead to a net warming, they must cause a net transfer of heat from the ocean to the atmosphere over multiple cycles. But, ocean temperature measurements have shown that over the period of interest here (the last few decades) the heat content of the ocean has increased not decreased (see http://www.realclimate.org/index.php/archives/2008/06/ocean-heat-content-revisions/).
And so, the ocean has taken heat from the atmosphere not the other way around, and so El Nino/La Nina, whether tied to the solar cycle or not, cannot be invoked as an explanation for global warming.
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