Global Warming: Man versus Sun?

Browsing a few of my favorite Internet news sources earlier this week (some left leaning, some right leaning, some not leaning, and one 'fair and balanced') I came across Drudge's link to this DailyTech blogpost on evidence for global cooling.  That's right, there is scientific evidence for global cooling.  Or so DailyTech claims:

Over the past year, anecdotal evidence for a cooling planet has exploded

...and the reason for cooling?  The sun.

Scientists quoted in a past DailyTech article link the cooling to reduced solar activity which they claim is a much larger driver of climate change than man-made greenhouse gases. The dramatic cooling seen in just 12 months time seems to bear that out. While the data doesn't itself disprove that carbon dioxide is acting to warm the planet, it does demonstrate clearly that more powerful factors are now cooling it.

Intrigued I decided to dig further.  Is it possible that sun activity swamps any effects of CO2?  Let's take a look.

DailyTech's compiled evidence focuses on this graph (click for larger):

As you can see (and as highlighted by the big blue line on the graph), there seems to be a dramatic decrease in temperatures from January 07 to January 08.  Pretty convincing when viewed in isolation.  But I'm not one to view things in isolation (unless it's the Sports Illustrated Swimsuit Edition...oops, TMI).  So I decided to go the source data and see for myself.

DailyTech's evidence focuses on a compilation of readings from four sources* of global surface temperature data.  Not knowing much about three of the four sources I will focus my attention on the data from NASA--a fairly reputable source in my opinion.

On their web-site, NASA provides the monthly Global Land-Ocean Temperature Index from 1880 to Present.  To convince myself I know what I'm doing Using that data, I duplicate below the equivalent of DailyTech's graph using NASA's data (global surface temperatures 1988-January 2008):

So far so good, it looks like the NASA data shows the same thing and I can draw a graph in excel and export it as a jpg for your viewing pleasure.

Yep, there's a dip in 2007-2008. One point for DailyTech.  But wait, there's more.  If you expand the graph back to 1880, a different pattern emerges.  I've taken the liberty to add a trend line to make my point.

   

Even though there appears to be a noticeable dip in temperatures over the past year, there is a long-term trend at work, and that trend is noticeably upward.

Don't get me wrong, I'm not claiming that we're not in a cooling cycle.  Just that one year out of 220 does not a trend make. 

But, that's not the bigger point.  The DailyTech post cites articles that claim that sun activity is responsible for the downturn and seems to imply that in the long-run, sun activity has much more influence on temperature than CO2.  Is that true?  Keep reading, because I don't think the evidence backs it up.

To check the relationship between global surface temperatures and atmospheric CO2 concentrations, I will use the National Oceanic and Atmospheric Administration's monthly mean CO2 concentrations** measured at the Mauna Loa (yummy macadamia nuts!) Observatory in Hawaii.  Observations are only available from January, 1958 to December, 2007 but that's at least 30 years longer than the timeframe the DailyTech sources show. 

The graph to the left maps the trend in CO2 concentrations (right axis) and the trend in temperatures (left axis)on the same graph.  The trends are clear.  CO2 and temperatures are both increasing.  Some might be tempted to conclude that this is evidence that CO2 concentrations cause increasing temperatures.  I am not one of them.  First, the two vertical axes can't be compared, other than to note they increase from bottom to top.  Different scales render direct comparisons difficult.  Second, even if scaled comparisons were possible, the graph simply implies correlation, not causation.  In econspeak, correlation is a necessary condition for causality, but not sufficient.  More on this in a minute.

A scatter plot of CO2 concentrations and temperatures provides further evidence of this correlation (left). Clearly there is positive correlation between temperatures and CO2 concentrations, but there are three possibilities for this correlation: 1) CO2 causes higher temperatures, 2) Higher temperatures cause higher CO2 concentrations, 3) Something else causes higher temperatures and higher CO2 concentrations (spurious correlation).  Without much more information we can't figure out which of these three are true and this is beyond the scope of what I want to talk about here.  Instead, I will leave it as at least an unproven possibility that higher CO2 concentrations cause higher temperatures.  That will be enough to prove my point later.

So what about sun activity?  To investigate the relationship between sun activity and temperatures I will use more data from NASA.  This time from the Solar Physics Program at the Marshall Space Flight Center.  The next graph shows the monthly average sunspot count and the global temperature data on the same graph.  To make a relevant comparison I only use 1958 to present although sunspot data is available much longer. 

The cyclical nature of sunspots is clear.  Since 1958 there have been four peaks and four valleys and consistent with the DailyTech post, it looks like we are currently in a low activity cycle. 

Less clear, but at least at first glance, it also looks like there is little trend in long-term sunspot activity.  So I am tempted to claim that any effect of sun activity on temperatures would have to be short-lived because of the non-trending cycle.  But not yet.  First, take a look at the scatter plot of sunspots versus temperature (left).

While there is no obvious correlation (no detectable upward or downward trend in the data), a very interesting pattern emerges.  In periods of low sunspot activity, the variability in temperatures is much greater than periods of high sunspot activity***.  Sunspot activity may add to temperature variability, but there appears to be no contribution to the trend.    In other words, sunspot activity may cause temperatures to fluctuate more or less around a long-term trend, but something else is causing the trend. 

Finally, to rule out sunspots as the cause of spurious correlation between CO2 and temperatures, the last graph shows the relationship between monthly changes in CO2 concentrations and monthly changes in sunspot activity.  No correlation (as shown by the flat trend line).

So what's my conclusion?  First a disclaimer:

Disclaimer:  I have proven nothing here. Just providing anectotal evidence for discussion.  If I were trying to prove my result I would run a regression and show that everything I have said here holds up statistically--in the env-econ blogging sense of statistics.  But that would just be bragging.  Feel free to draw your own conclusions.

Follow the bouncing ball of logic.  C02 concentrations and temperatures are correlated.  Sunspot activity and temperatures are not and neither are CO2 concentrations and sunspot activity.  Therefore, sunspots activities are not a causal factor in determining long-term temperature trends. 

The current downturn in temperatures may be caused by a valley in the sunspot cycle.  But that doesn't mean that global cooling is taking place.  It just means that temperatures are likely to be more variable until sunspot activity increases again. 

In summary:

• Is there a long-term upward trend in temperatures? Yes.
• Is there a one year downturn in temperatures? Yes.
• Is the downturn caused by decreased sunspot activity?  Possibly.
• Is it just as likely that the same decrease in sunspot activity will cause a temperature increase next year?  I'm nodding.  But it might cause a lower temperature too.  That's what variance does.
• Do sunspots have an effect on the long-term temperature trend?  Nope.
• Does CO2 cause temperature changes?  I have no idea, but I know they're correlated.

*UK's Hadley Climate Research Unit, NASA's Goddard Institute for Space Studies, University of Alabama Huntsville and Remote Sensing Systems of Santa Rosa

**According to NOAA, "Data are reported as a dry mole fraction defined as the number of molecules of carbon dioxide divided by the number of molecules of dry air, multiplied by one million (ppm)."

***Those versed in econometrics will notice the classic heteroskedasticity cone shape.

Comments

[Kristopher Kubicki]

Hi Tim,

I applaud your concise and thorough analysis of the data. I have a couple of corrections and observations for you:

"DailyTech claims that sun activity is responsible for the downturn and seems to imply that in the long-run, sun activity has m,much more influence on temperature than CO2."

Well, nobody at DailyTech ever said this, although it was postulated in our forums. Dr. Kenneth Tapping's data indicates a correlation between sunspot activity and temperature, though on much different scales:

http://www.dailytech.com/Solar+Activity+Diminishes+Researchers+Predict+Another+Ice+Age/article10630.htm

"Not knowing much about three of the four sources I will focus my attention on the data from NASA--a fairly reputable source in my opinion."

The GISS data is compiled, in part, by the Hadley data. This is generally why researchers compile GISS and Hadley data together in a plot. The other two sources are satellite data, but their measurements only reach into the late 1970s.

Thanks for the mention!

Kristopher

[Tim Haab]

Kristopher,

Thanks. Sorry for the slip. I try to stay objective for once and end up anything but...didn't mean to blame DailyTech. I changed "DailyTech claims..."

"The DailyTech post cites articles that claim..."

Tim

[Ironman]

Oh come now. All the analysis you provided in this post was just an excuse so you could use the word "heteroskedasticity."

Now, if you could use it in a regular Friday beer post, then you might be on to something!...

P.S. Nicely done!

[John Whitehead]

Tim,

Why do you make your research assistant do so much work?

[Tim Haab]

Really wasn't much work. The hard part was figuring out how to get the rows of temperature data into a single column so I could graph it. Finally remembered proc transpose.

As for research assistants, Imake them do my real work so I can free my time for the fun stuff like this.

[JBK]

You may want to plot temp vs the length of the solar cycle. I've seen a paper which gets fairly good R^2 values out that comparison. .5 to .7 IIRC

The longer the cycle the cooler it gets.

As for the CO2--Temp correleation it is hard to explain why temp dips in the 1950s and 1970s while CO2 increases steadily.

[Steve Bloom]

KK: "Dr. Kenneth Tapping's data indicates a correlation between sunspot activity and temperature, though on much different scales"

This an utter fabrication lifted from an Investor's Business Daily "editorial" (and without attribution, too). Tapping described this distortion of his views as "garbage." Deltoid documents how this crap reverberates through the denialosphere.

BTW, Tim, the solar crazies argue that it's not the sunspots per se but rather the increase in cosmic ray activity that occurs when solar activity is low (this according to them resulting in a significant cooling effect on climate via increased low cloud formation). Unfortunately for them, the fact that we can directly measure cosmic ray activity during the present solar low means that they're about to be whacked in the face by the 2x4 of reality. It'll be amusing to watch.

(I should mention that it is generally believed by climate scientists that there is probably a *minor* effect of cosmic rays on cloud formation and temperature. This is why the CERN study got funded.)

[joshua corning]

For the record i am not posting on this intentionally...it was not because I did not see or read the post.

[Adrian]

Hey just stopping by to get my dose of green info. Always good stuff here! Love it. I know I have mentioned this site before but I think they are pretty cutting edge so I wanted to share this page: http://www.earthlab.com/articles/EarthsVitalSigns.aspx.

I was hoping that someone could drop me a link of other reports that might tell us about how much time is left before we can’t fix global warming? EarthLab.com has a pretty could article here but I want some other opinions. Man just think how the bad will be if we don’t prevent this. EarthLab has quite a few tips on how to lower your impact, here is a spot where they list what their readers recommend: http://www.earthlab.com/life/tips.aspx.

Thanks a lot for all your info and drop me a link if you guys see anything on these subjects.

[gormk]

Tim –Very cool blog/analysis.

Maybe you know this already. There is a very controversial movie dedicated to this and other “alternative” climate change hypotheses titled: The Great Global Warming Swindle.

http://en.wikipedia.org/wiki/The_Great_Global_Warming_Swindle

I showed this movie, and Al Gore’s An Inconvenient Truth, back-to-back in my undergraduate environmental economics course last semester to generate student thinking and discussions about climate change. [The “Swindle” hasn’t been released in the US yet, so I had to get it via Amazon UK…]

As an aside: Coming into the course, the attitudes towards climate change among 18 students (many from Colorado farm families) were as follows:

Global climate change is real, but NOT caused by human consumption and production activities. (N=1)
Global climate change is real, AND human consumption and production activities contribute significantly to it. (N=16)
Global climate change is NOT real. (N=0)
I am not sure whether it is real or not. (N=1)

Unfortunately, I didn’t conduct a post-movies attitude survey…

[James Dill]

Here is a scientist who seems to disagree with you:

http://www.sciencebits.com/CO2orSolar

[Steve Bloom]

James Dill, Shaviv is operating outside his field of expertise. For these purposes, he's a crackpot.

[James Dill]

Aren't Tim Haab and John Whitehead operating outside their field of expertise? For these purposes are they crackpots? Nir Shaviv (Hebrew: ניר שביב‎) is an Israeli associate professor of physics, carrying out research in the fields of astrophysics and climate science. I would say all three are are worth listening to. If Steve Bloom is so smart refute Shaviv.

[Steve Bloom]

Shaviv has been refuted to death at RealClimate by people far more qualified than I. The posts are easy to find via a site search on his name.

BTW, Shaviv may be an astrophysicist, but he's a bit thin on colleagues who think there's much to his ideas. He is no kind of climate scientist.

I agree that Tim is very much worth listening to on these data-crunching issues, as it doesn't require advanced knowledge of the underlying science.

[D Kelly O'Day]

Tim:

Very nice job!

As a data visualization and global warming analysis hobbyist, I have recreated your analysis in a downloadable Excel workbook.
http://processtrends.com/toc_chart_doctor.htm#Env_Econ_gw

All are invited to download and see what else they can do with the data.

D Kelly O'Day

[Simon D]

Your statistical analysis appears quite while well-intentioned, but misses some basic atmospheric and solar physics and ignores the all-important time dimension.

In examining the role of different factors - solar output, greenhouse gas concentrations, etc - on the global temperature, you have to first look at the magnitude of the change or variability in those factors over time. For example, the recorded sunspot activity only cause a 0.01% change in the solar constant - the measure of the sun's output - which equates to only a small fraction of the change in energy (or global temperature) since the 1950s. It is the small magnitude of solar variability, not the existence or lack of a correlation, which shows that sunspot activity cannot explain the observed temperature change.

On the time question, the calculated temperature-CO2 correlation presumes that the climate instantaneously responds to changes in CO2 concentration. The climate system does not work that fast. Everything we know about the physics of fluids - air and water - and the circulation of the atmosphere and oceans shows that it takes time for the climate system to respond to an external forcing like an increase in CO2 concentrations in the atmosphere. So, yes, there's strong a relationship between temperature and CO2 going back over time... but you won't find a clean one-to-one correlation using annual data.

[Eric Torres]

One data point does not make a trend. I teach that every day (Mathematics Prof.) Please take a look at the following link from Wikipedia.

http://en.wikipedia.org/wiki/Image:Ice_Age_Temperature.png

You can find many other reconstructions of ancient temp's from Ice cores at other sites as well.

Quiz: Can any one with out any knowledge other than the graph predict if the Earths surface temp should be going up or down, if man has no impact?

Answer: Up, then down. It will get cold like the trend for the last 450k yrs shows. It should be hot like the trend for the last 450k yrs shows.

There is no Statistical evidence that the current change in temp is deviating from EXPECTED.

You are correct 1-4 years too limited of view. But why limit it to any thing less the 450k yr of accurate weather? Are you just being convenient as well?

[Ken]

Nice post Tim. It shows that your economics education provided you with a much better understanding of statistics and numerical analysis than some of the TV meteorologists on the blogsphere trying to do the same thing, but with the clear intent of "proving" AGW wrong.

[Ian]

Eric Torres, you say that there's no statistical evidence of a departure of current temps from a longer-term pattern of variation. This is a rather strong claim. Could you be more specific about what data and statistical tests you've run?

In addition, did you know that the graph you’ve linked only includes data through 1950? And, you should realize that the scaling on the graph you've linked - it's too compressed to represent the past 150 years, given pixel width. Have a look here for a clearer comparison - http://commons.wikimedia.org/wiki/Image:Carbon_Dioxide_400kyr.png . Incidentally, the graph you linked comes from this paper: Petit J.R. et al.. (1999). Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica, Nature, 399: 429-436. The last sentence of their abstract is: “Present-day atmospheric burdens of these two important greenhouse gases (methane and CO2) seem to have been unprecedented during the past 420,000 years.”

Second, you might want to acquaint yourself with some of the science behind climate change - I'd suggest the IPCC reports at http://www.ipcc.ch/ - in particular, the "Physical Science Basis Report." It should give you a sense of how basic scientific findings, such as the thermodynamics of CO2, and the changing isotope concentration of the atmosphere, all point toward a warming trend that will continue for a while.

[James Dill]

I wonder if you could comment of this:

http://rankexploits.com/musings/2008/ipcc-projections-overpredict-recent-warming/

[Mike D.]

Here is some data, showing a long term trend connecting sunspot activity to global warming. At the end of the day it always comes down to one question: where does all the data come from and how carefully and objectively has it been processed.

http://wasteofmyoxygen.wordpress.com/2007/11/06/solar-cycles-seasonal-co2-levels-not-humans-global-warming/

[Roy McCanne]

Of the three global temperature scales (GISS, NCDC and HadCRu) your graph is clearly the HadCru alone. HadCru is flawed because it contains no data on the Arctic and that's where the warming was in 2007. GISS showed warming and NCDC was neutral. The British Meteorological Office reported this January that 2007 was the hottest year ever recorded. I am unable to accept your data or conclusions.

[James Dill]

here is an interesting article:
http://bourabai.narod.ru/landscheidt/new-e.htm

[James Dill]

here is an interesting article:
http://bourabai.narod.ru/landscheidt/new-e.htm