Global Warming: Man or Myth?

Scientists can also wear their citizen hats

Chopping Down the Cherry Tree

with 25 comments

The image above shows a cherry tree with 96 red cherries and 4 blue cherries.  If somebody asked me or another scientist what type of tree this is I would state:

“It is very likely to be a red cherry tree and I am investigating why there are a few blue cherries that do not appear to fit in.”

Similar statements have been made by scientific experts regarding climate change:

 “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”  (IPCC, 2007)

“Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.”  (IPCC, 2007)

The term very likely used by the IPCC means a probability greater than 90%.

A poll performed by Peter Doran and Maggie Kendall Zimmerman at Earth and Environmental Sciences, University of Illinois at Chicago of 3,146 Earth scientists showed 96.2% of climatologists who are active in climate research believe that mean global temperatures have risen compared to pre-1800s levels, and 97.4% believe that human activity is a significant factor in changing mean global temperatures.

For more information about the scientific consensus regarding climate change please see The Scientific Consensus.

So if this red cherry tree is so obvious why do we still have some people trying to tell us that it is a blue cherry tree?  This technique is called cherry picking data to support a false claim.

A few notable examples of cherry picking appear below.

1)  “Global Warming Stopped in 1998” or “There Is Global Cooling”:

If I were determined to show global cooling, I would choose 1998 as a starting point and then 2008 as my ending point.  Why?  1998 was a strong El Niño year which caused a very warm signal and 2008 had a strong La Niña which caused a very cool signal.   Here is what the four major global temperature plots look like when I “cherry pick” the data:

Global surface and lower troposphere monthly mean anomalies and linear trends between 1998 and 2008

Three of the four global average temperatures indeed are decreasing in their trends (although the actual global mean temperatures are still warmer than the previous decades).

So what happens if I start with the year 1999 and end with the year 2009?

Global surface and lower troposphere monthly mean anomalies and linear trends between 1999 and 2009

Simply by shifting our starting point by one year, all four global average temperatures are increasing in their trends! The point made here is that if one cherry-picks a small subset of the data, one can make just about any claim with a nice plot to back it up. The correct way to view global temperature trends is to look at ALL of the data.

Global surface and lower troposphere monthly mean anomalies and linear trends since 1880

For more information please see Global Cooling.  The bottom line is that 20 of the warmest years on record have occurred in the past 25 years. The warmest year globally was 2005 with the years 2009, 2007, 2006, 2003, 2002, and 1998 all tied for 2nd within statistical certainty. (Hansen et al., 2010) The warmest decade has been the 2000s, and each of the past three decades has been warmer than the decade before and each set records at their end. 

Looks like a red cherry tree to me!

2)  “Arctic Sea Ice Has Been Increasing Since 2007!”

Northern Hemisphere sea ice extent since 1953

The image above from the National Snow and Ice Data Center indeed shows that ice extent has increased from a record low in 2007 but, of course, the long-term trend is steeply downward since the 1970s.

Sea ice extent is just part of the picture. Sea ice thickness has also been measured by declassified submarine records and ICESat satellite measurement. 

Northern Hemisphere sea ice thickness submarine & ICESAT combined (Kwock & Rothrock, 2009)

The figure above shows the mean thicknesses of six Arctic regions for the three periods (1958–1976, 1993–1997, 2003–2007). Thicknesses have been seasonally adjusted to September 15.  This combined analysis shows a long-term trend of sea ice thinning over submarine and ICESat records that span five decades.

Looks like a red cherry tree to me!

3)  “Greenland and Antarctica Are Gaining Ice at Their Centers”

Yes, ice mass is increasing in the centers of both of these ice sheets.  However, when one considers the mass of these ice sheets in their entirety, a different picture emerges:

Greenland Ice Mass Loss (Velicogna, 2009)

Antarctica Ice Mass Loss (Velicogna, 2009)

It is quite clear that, overall, Antarctica and Greenland show a long-term loss of ice.

John Cook at Skeptical Science has several very good summaries of this research. See: An overview of Antarctic ice trends, An overview of Greenland ice trends, and Why is Greenland’s ice loss accelerating?

Looks like a red cherry tree to me!

4)  “The                         Glacier is Advancing!”  (Fill in the blank with your favorite advancer)

There are indeed some glaciers around the world that are advancing.  Yes, there are a few blue cherries on our red cherry tree.  Let us look at ALL of the glaciers around the world that are being monitored by the World Glacier Monitoring Service.

Mean cumulative specific mass balance of all reported glaciers (black line) and the reference glaciers (red line)

It is quite obvious that glacial mass is rapidly decreasing.  So what about the claim that some glaciers are advancing?  According to the WGMS, 90% of worldwide glaciers are retreating.

Looks like a red cherry tree to me!

So what are your favorite examples of cherry-picking?

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Written by Scott Mandia

February 20, 2010 at 1:46 pm

Posted in Uncategorized

25 Responses

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  1. what’s interesting when one thinks about, are the strong negative anomalies at the start of full observational temp. series (late 1880’s). they are essentially equal and opposite in magnitude to the current warm anomalies! thus making them rather ordinary (in terms of the magnitude of the anomaly) within this limited dataset.

    can we agree that the cool anomalies were not caused by man? if so, then this also shows how the natural system has strong internal variations in the negative, so why couldn’t it have strong internal variations (of similar magnitude) in the positive?

    jfr117

    February 20, 2010 at 8:00 pm

    • Please see this thread from Skeptical Science: It warmed before 1940 when CO2 was low and the linked papers found there.

      Scott Mandia

      February 21, 2010 at 12:59 am

      • i was talking about the cool anomalies, not the subsequent warming trend. what caused the cool anomalies, nature, i presume.

        Mandia: Yes, it appears that a weaker sun and more frequent volcanic eruptions caused a cooler late 1800s.

        btw, the two linked papers there contradict each other: one says no net anthropogenic impact, the other one says partial antrhopogenic impact.

        Mandia: I pointed you to that link and to those papers to show you that, yes, there are natural forcing mechanisms at work, but they are being dwarfed by human effects in the last several decades.

        jfr117

        February 21, 2010 at 8:10 am

    • “there are natural forcing mechanisms at work, but they are being dwarfed by human effects in the last several decades”…that statement is false for the last 12 years.

      Mandia: Several decades is not twelve years.

      The monotonic increase in co2 is NOT being matched by the temp. series during this period due to natural causes.

      Mandia: 12 years cannot define a trend with significance. The minimum time period to have the trend stand out from the noise is 15 years but 30 years is usually considered to determine climate trends. There has been nothing in the past 12 years that suggests that CO2 is not important.

      In fact, 2009 was tied for the 2nd warmest year ever and that year saw the weakest sun in 100 years. 20 of the warmest years on record have occurred in the past 25 years. The warmest year globally was 2005 with the years 2009, 2007, 2006, 2003, 2002, and 1998 all tied for 2nd within statistical certainty. (Hansen et al., 2010) The warmest decade has been the 2000s, and each of the past three decades has been warmer than the decade before and each set records at their end.

      jfr117

      February 21, 2010 at 3:42 pm

      • What is your background that makes you think that you are seeing something that none of the experts see? Which sources are you using for your information?

        I suggest reading everything on my Web site very carefully before you post on blogs such as this one. It appears to me that you may be parroting things you are reading on non-scientific Web sites. I hope I am wrong about that assumption.

        I also suggest that you visit the links below to better understand trend analysis:

        http://tamino.wordpress.com/2009/12/07/riddle-me-this/

        http://tamino.wordpress.com/2009/12/15/how-long/

        http://tamino.wordpress.com/2009/06/26/embarrassing-questions/

        This man is a world-class statistician and very well-informed regarding the science of climate change. I have learned much from his lucid blog posts.

        Scott Mandia

        February 21, 2010 at 5:15 pm

      • my background is in meteo from psu, same as you. while you and people like tamino treat recent trends and non-conforming data as noise to be disregarded, i think the past decades weather is important and shows many things about the physical mechanisms that do control the earth’s climate.

        i am not as arrogant as you in my conclusions.

        i don’t know who tamino is, but i think he is the most condescending of your sources. much like you would feel sick reading a ‘skeptic’ blog, reading him is hard to bear.

        Mandia: When I first began reading climate blogs, I thought Tamino to be too harsh also. However, I can understand his attitude because it does get tiring when people make unsupported claims or do not accept the helpful advice they get from those that are expert. (BTW, I am not referring to you here.) Furthermore, because climate change is such an important crisis facing humanity as we move toward 2100, it just adds to the frustration and Tamino has no time for the ignorance and he lets you know that. Although it may be difficult for you to read, the statistical methods and the data he reveals are world-class. Imagine if Einstein were insulting – would you refuse to accept his physics?

        The bottom line is that Tamino takes much time to show average people how to analyze data and why the experts are correct and why most of the skeptics’ arguments are false. And he does all of this for essentially no fee.

        i thought you might be different and i could engage you in discussions, but it is evident that you don’t have an ‘open mind’ and in fact are close minded. good to know that real science is being pushed forward at your school. you have no objectivity – you are blinded by fear and emotion. why you can’t raise or handle questions is beyond me. sad day.

        Mandia: I think this is unfair based on the conversations we have had.

        jfr117

        February 21, 2010 at 7:55 pm

      • starting at 1975 to 2010, 12 years is 34% of the time, keep treating real data as noise instead of figuring out what is really going on. great science…never challenge anything, scott.

        Mandia: “What’s the use of having developed a science well enough to make predictions if, in the end, all we’re willing to do is stand around and wait for them to come true?”
        — Nobel Laureate Sherwood Rowland (referring then to ozone depletion)

        Scientists have figured out what is going on and there is no time for delay. There is never 100% certainty in science, as you know, so we need to stop wasting valuable mitigation time trying to reach the impossible. The debate has moved on from “What is causing the warming” to “What can we do to mitigate the damage and how bad is it going to get if we do not?”

        jfr117

        February 21, 2010 at 8:01 pm

      • Mandia: “I think this is unfair based on the conversations we have had”

        …your appeal to elitism (what could i possibly see or question that ‘experts’ have not seen or questioned…and don’t post on blogs until you agree with all our points…and if you don’t agree, its unscientific) is what made that fair.

        your message is, and will always be, questioned because it is delivered with arrogance and alarm. although the science is settled for you, it is not for everybody. i am glad that i can ask questions and be open to discussions, that is what got me into science.

        the beginning of climate trends must start with the weather, what use is a science if it can’t forecast new trends? the past 12 years have no trend (it cannot be distiguished from the error)…we are at a warm plateau…not monotonically increasing. sorry, deal with it.

        jfr117

        February 22, 2010 at 9:18 am

      • This is my blog so I reserve the right to have the last word. I think this thread has gotten too personal so I will not be allowing any more comments that I deem as not adding to the discussion.

        jfr, you have misinterpreted my comments. I asked you to read my Web site to better understand why there is such a consensus for AGW. That will put you in a better position to ask questions on blogs such as this. I did not suggest that you have to agree with everything and if not do not bother to post. Haven’t I tried to engage you in every comment? My question about your background was a mistake because you did tell me in a prior post that your were a PSU meteo alum. I am sorry that I forgot.

        I looked you up and found your weather page. How come you do not list your PSU credentials if you are an alum? (BTW, I have been to Asheville a few times and it is one of my favorite towns. My brother-in-law lives there and my in-laws have a summer home there. Highland Brewing Co. is one of my favorites!)

        I think your weather forecasting expertise is actually causing you to not see the forest because of the trees. In fact, I think one of my next posts will be about why meteorologists as a group are some of the biggest skeptics. Oil industry geologists are the most skeptical scientists. I wonder why. Anyway, do you agree that it is easier to predict that June and July will be warmer than February than it is to predict whether it will be warmer in the next five days than the last five days? When it comes to trends in climate, weather is noise. No question about it. Natural cycles can amplify or dampen trends, but they are not determining the long-term trend. There is no evidence for it but multiple lines of evidence for increasing GHGs.

        Scott Mandia

        February 22, 2010 at 11:47 am

      • i’m not sure who you think i am, but i don’t live in asheville and i don’t forecast! i am a consulting meteorologist in new england.

        jfr117

        February 22, 2010 at 3:09 pm

      • Strike two on me then! I did a Google search for jfr117 and came up with somebody else who is a meteorologist and has those initials. Sorry.

        Scott Mandia

        February 22, 2010 at 4:30 pm

  2. Excellent post Scott. It seems crazy (and rather sad) that we now have 30 years of consistently rising global temperature and we still have people saying “Look, it didn’t warm in the last 5 years, global warming is a hoax!”.

    Icarus

    March 7, 2010 at 10:05 am

  3. Scott,

    Thank you. Got here via RC. Excellent analogy. I’ll steal it, thank you very much. Would you mind if i mirrored this entire post to my blog?

    Cheers

    ccpo

    March 7, 2010 at 6:57 pm

    • Take whatever you want. We are all here for the same reason: getting the truth out there. :)

      Scott Mandia

      March 7, 2010 at 7:08 pm

  4. EVERYBODY PANIC!!

    Not.

    After being serially debunked on WattsUpWithThat, Mandia attempts his globaloney on his friendly echo chamber.

    Apparently the WUWT kitchen is too hot for a pampered academic sucking at the public teat.

    But baloney still baloney: there is ze-ro empirical, testable evidence showing that CO2 has any measurable effect on the planet’s temperature. Do you understand what “zero” means?

    All of the so-called “evidence” comes from always-inaccurate GCMs [computer climate models]. Garbage In, Gospel Out. But models are not evidence.

    I invite Mandia to come on up to WUWT to spout his nonsense again. We miss having Mr Piñata at the internet’s “Best Science” site.

    So c’mon, schoolboi, what’re you scared of? The truth?

    I’ll be waiting to set you straight again — on a site where the site owner doesn’t jump in and opine at every comment, as if that makes your silly CO2=CAGW conjecture anything but baseless globaloney.

    Smokey

    March 22, 2010 at 7:58 am

    • It is true that I used to comment at WUWT, but it got very time-consuming responding to comments such as yours that offer no useful information. In fact, the plot you link to proves you to be wrong and you do not even realize this. Of course, the y-axis labelling shows the person who did the plot is either deficient in his knowledge of plotting data or is trying to intentionally mislead. Why not just set the y-axis range from 0 to 100 and get a flat line?

      Here is the CORRECT way to do the plot of global temps from 1979 onward:

      Global Temperature Anomalies & Trends Since 1979

      Notice anything?

      There are a few commenters at WUWT that I respect but you are certainly not one of them.

      Scott Mandia

      March 22, 2010 at 8:25 am

      • I would like to add, the many dips that were not a sign of the end of warming, but were, in fact, signs of the effects of natural variations. To the denialists, please explain why the dip between about 81 and 83, between about 92 and 93, between 98 and 00 did not result in a plunge into an ice age.

        If you can get this, you might just start to understand trends. Actually, I think you do understand trends, but are quite simply intentionally misleading others. How do I know this? Because understanding what a trend is and that the temps of the last ten years do not indicate cooling is a dead simple. I can teach this stuff to 3rd graders and they get it.

        Occam’s razor applies.

        Cheers

        ccpo

        March 22, 2010 at 10:48 am

      • -snip-

        Mandia: Smokey, I will not allow you to post the same tired memes here that you do at WUWT. Your comments add nothing to the discussion. Bye bye.

        Smokey

        March 22, 2010 at 2:45 pm

  5. […] due to much colder weather.  The author is comparing apples to oranges and is exhibiting classic cherry-picking by choosing a single month in a single year while ignoring the long-term decreasing trend in sea […]

  6. Hi Prof. Mandia,

    I’m not sure if this helps in the above conversation, but I made a visualization that shows short term trends for the past 30+ years. It’s clear that we’ve had short term cooling in the past; so if anyone is to refute the “current” (98~08) cooling that it is different from past coolings, one would certainly need to look further than global surface temperatures.

    apeescape

    June 13, 2010 at 3:09 pm

  7. sorry, link to image doesn’t work.

    apeescape

    June 13, 2010 at 3:10 pm

    • appescape,

      This is an excellent way to view trends over the record. I thank you for adding to this discussion.

      Have you seen the cool Java applet from CTG Software, KTD. that I added to my Global Cooling page? Click the link and scroll about 1/2 way down.

      Scott Mandia

      June 13, 2010 at 3:33 pm

  8. […] was perhaps the students were trying to curry the favour of their professor who suggested the idea of using the cherry tree. But then I attended a climate change communication workshop hosted by the Bureau of Meterology. A […]

  9. […] was perhaps the students were trying to curry the favour of their professor who suggested the idea of using the cherry tree. But then I attended a climate change communication workshop hosted by the Bureau of Meterology. A […]

  10. […] Imagine a cherry tree with 96 red cherries and 4 blue cherries. If somebody asked me or another scientist what type of tree this is I would state: “It is very likely to be a red cherry tree and I am investigating why there are a few blue cherries that do not appear to fit in.”  A cherry-picker will just show you the blue cherries to convince you otherwise.  (A few examples are illustrated in my post Chopping Down the Cherry Tree.) […]


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