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This item was posted on February 13, 2010, and it was categorized as Climate Change, Global Warming, Global warming skeptics.
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But skeptics misuse this statement to claim there has been no warming

statistically-significant

In an interview with the BBC, Phil Jones, the embattled director of the British Climatic Research Unit, said that an observed warming trend of 0.12 degrees C per decade between 1995 to 2009 was “not significant at the 95% significance level.” On the other hand, he said, it was quite close to being statistically significant.

Predictably, the deniosphere jumped all over this. For example, here was Marc Morano’s headline at Climate Depot:

The Jig is Up! Climategate U-turn as Phil Jones admits: There has been no warming since 1995.

Either Marc knows nothing about statistics, or he is deliberately twisting the facts — or both. Phil Jones simply did not say that there has been no warming since 1995.

A 95 percent significance level simply means there is actually a 5 percent chance of a particular finding occurring purely by chance. So here’s what Jones is saying, in essence: There is a very slightly greater than 5 percent chance that the measured warming of 0.12 degrees C per decade between 1995 and 2009 was a statistical fluke — in other words, not real.

Or flop it around: There is a slightly less than 95 percent chance that the observed warming actually happened.

By convention, 95 percent significance often is considered “good enough to be believed.” But this is purely arbitrary, and it does not mean that something with a 94 percent significance level is categorically untrue. If a doctor told you that there was a 94 percent chance that you would die of cancer unless you underwent a particular treatment, what would do? Would you say, “Well doc, if there was a 95 percent chance, I’d accept the treatment, but since it’s just a 94 percent chance, I’ll decline”?

Somehow, I doubt it. I think you’d probably take the treatment.

The problem with the temperature record between 1995 and 2009 probably is not that there has been no warming during that period. The problem, as Jones told the BBC, is this: “Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.”

You probably won’t hear that important statement from skeptics like Marc Morano, or from the news media for that matter. But it’s important, because it emphasizes a crucial fact: Climate change is best documented over the course of decades, not years. And over the course of decades, Jones told the BBC, the a chart Jones provided to the BBC at their request shows a clear trend: During four distinct periods since 1860, the climate warmed at a rate of approximately 0.163 degrees C per decade.  The global climate has warmed at a rate of approximately 0.163 degrees C per decade since 1860.

Here’s the chart:

jones-chart

I don’t know why the BBC asked only about these specific periods, and I also don’t know off the top of my head what the trend per decade was during the missing time in between 1880 and 1910, and 1940 and 1975. I will try to track those numbers down and post them when I can. (If any readers of CEJournal have the numbers, plus a reference to a reliable primary source, please leave a comment.)

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This thing has 23 Comments

  1. googler
    Posted February 14, 2010 at 6:07 am | Permalink

    Tom – please can you cut and paste the part of the interview where you got this from?:

    “And over the course of decades, Jones told the BBC, the trend is very clear: The global climate has warmed at a rate of approximately 0.163 degrees C per decade since 1860.”

    I can’t find it – apologies if I have missed it.

  2. h
    Posted February 14, 2010 at 1:11 pm | Permalink

    To Googler:

    Simply take the information from the data table near the top. Average the four trends.
    (0.163 + 0.15 + 0.166 + 0.161) / 4 = 0.16 degrees Celcius per decade since 1860, a trend that is indeed statistically significant.

    (If you factor in Jones’ stated, not-statistically-significant trend of 0.12C per decade for the period between 1995 and 2009, you can reach the figure of 0.163 degrees C per decade.)

  3. googler
    Posted February 14, 2010 at 2:27 pm | Permalink

    h – thanks but where does the quote come from?

    Also what are the trends for the periods not listed in the table? How do they contribute to the claimed rate from 1860?

  4. Posted February 14, 2010 at 2:34 pm | Permalink

    To h: Thanks for that. I was about to answer googler’s question, but you beat me to the punch!

    And googler: If the quote you’re asking about is the “not significant at the 95% significance level” one, it came from the BBC Q&A. The link is at the top of my post. His quote about “achieving statistical significance” comes from the same place. I believe those are the only two actual quotes in my post, so if you’re asking about something else, let me know and I’ll try to help.

  5. googler
    Posted February 14, 2010 at 3:45 pm | Permalink

    Hi Tom –

    1) I was looking for this:

    “…Jones told the BBC, the trend is very clear: The global climate has warmed at a rate of approximately 0.163 degrees C per decade since 1860.”

    2) If you were going to say what h said please can you answer this for him?:

    “Also what are the trends for the periods not listed in the table? How do they contribute to the claimed rate from 1860?”

    Thanks

  6. Posted February 14, 2010 at 5:49 pm | Permalink

    Googler: I clearly made a mistake! There are four periods in the graph, but they do not represent a continuous record. Time is missing between each of the four periods. (That will teach me to write a blog post at 12:30 a.m. on a Sunday morning, in bed no less, after drinking too much coffee late in the evening…)

    So all that can be said based on that table is that the trend for the four periods is about the same — 0.163 degrees C. The question is, why did the BBC only ask for the trends for those specific periods? I have no idea whatsoever. Anyway, time to correct my post…

  7. googler
    Posted February 14, 2010 at 7:32 pm | Permalink

    Thanks for correcting Tom but really I think it is pretty poor in a post on misrepresentation of statistics to do exactly what you are complaining about!

    Temp. info for various periods and from various data sets is here:

    http://www.woodfortrees.org/

    and this is a plot of HadCRUT from 1860 to present with a trendline on top:

    http://www.woodfortrees.org/plot/hadcrut3vgl/from:1860/to:2010/plot/hadcrut3vgl/from:1860/to:2010/trend

    I think one thing that the answer to the BBC question shows is that late 20th Century warming was not happening at an unprecedented rate.

  8. Posted February 14, 2010 at 8:09 pm | Permalink

    Come on Googler, cut a poor suffering warmist/alarmist some slack, would you? I made an honest mistake while blogging too late at night, hepped up on too much caffeine. No deliberate intent to mislead anyone. (The same cannot be said of most partisans who blog on this subject, including Marc Morano, who I correctly took on in this post).

    And besides, my overall point still stands.

  9. Posted February 15, 2010 at 8:13 am | Permalink

    Tom,

    Trends over discrete periods are always tricky, since the result depends a lot on how you choose the start dates. I’ve always been fond of this chart personally, which shows the trend from every year to 2009: http://i81.photobucket.com/albums/j237/hausfath/Picture88.png

    You can clearly see that as the period of years used to create the trend shrinks, you get a lot more variability. This is even more dramatic if you use monthly data (instead of annual averages) to create the chart.

    As a point of reference:
    1900-2009 trend: 0.0735 C per decade (similar to the 0.7 C warming this century cited by the IPCC, unsurprisingly).

    Data used is available from Hadley/UEA: http://www.cru.uea.ac.uk/cru/data/temperature/

  10. JRAN
    Posted February 15, 2010 at 11:35 am | Permalink

    my 2¢…

    What about the claims of missing and misuse of data that Jones is accused of in the Daily Mail article? It would seem that missing data and not allowing critics to see data is kind of shading in practice – and it did come back and bite Jones.
    How can his statistics be held as credible after such a huge withdrawal from his academic creditability?
    The Daily Mail also quotes Jones’ comment on the Medieval Warming Period and its probability of being a global warming period.
    I wonder why the climatology scientists are working together to clear up the science of this. Instead it seems to be divided into very dug in camps now. That is not science. That is politics.

  11. Posted February 15, 2010 at 2:55 pm | Permalink

    Tom – I am not impressed.

    The “If a doctor told you that there was a 94 percent chance that you would die of cancer unless you underwent a particular treatment” is misleading. Either we are discussing science here, or we are not. Therefore: are you trying to dismiss the long-standing convention of not accepting as “positive” those results that have less then 95% significance? If you are, what are your (scientific) reasons for doing so?

    You might want to clarify to your readers the reasons for that long-standing convention.

    ps love the T-shirt…and it is sporting a p<.001 …

  12. googler
    Posted February 15, 2010 at 3:10 pm | Permalink

    Zeke – what do you make the trend from 1860?

  13. Posted February 18, 2010 at 1:29 pm | Permalink

    Why did the BBC ask about those particular periods? Well, if you look at the other questions, it appears that the BBC was wanting to get Jones respond to various implied contrarian talking points. I’m not sure that was a helpful approach, since everyone just cherrypicked what they wanted to anyway in order to twist the facts. I’d be curious if Harrabin really thought these talking points had validity, or whether he thought them bogus, but requiring clear refutation. But anyway …

    One of those talking points is based on the the idea that warming periods have alternated with cooling (or at least “flat”) periods. If the “warming periods” are of similar trend, then, it is held, that means that rising GHG concentrations can not account for these trends.

    That’s why Jones specifically added 1979-2009 trend – to show that the long term trend has not budged much since 1998. In fact, if you take the linear fitted trend from 1975-1995 and from 1995-2009, you’ll see that both (paradoxically) are lower than 1975-2009 (a mild instance of Simpson’s paradox).

    As to why the BBC chose 1995, that was presumably a cherrypicked date to come out just below significance.

    As for cooling since 2002, well, you get the idea …

    Jone’s statements about trends and the MWP are being covered as a “confession” or “admission” that he has changed his position on these issues. This is the case even for those who avoid Morano’s blatant lie and talk about “no statistically significant warming”.

    Of course, that’s ludicrous; Jones’s position has not changed on the MWP nor human attribtion of recent warming and is essentially no different from IPCC AR4. Isn’t that the main point here?

    (BTW, perhaps I missed it, but have you covered the various accusations of quote fabrication that several scientists have levelled against U.K. journalists? Thanks!)

  14. Posted February 18, 2010 at 2:21 pm | Permalink

    Deep Climate: Yes, I did cover the fabricated quotes. The hed was “Another scientist caught in the maw of climate politics — and yellow journalism.”

    This is one reason why Gavin Schmidt’s attack on me over at RealClimate was so unfounded. If you didn’t see it, he accused me of advocating a “pell mell rush into the fact-free abyss.” My infraction: Saying that the U.S. press should stop ignoring the IPCC controversy and set the record straight. For whatever reason, he took that to mean that I was advocating yellow journalism.

    I’ll tell you, the climate wars are no fun. I try my best to to be fair, accurate, appropriately balanced and civil. And I’ve been trying hard for almost 30 years to get the story right. Sometimes I make mistakes. But Schmidt accusing me of advocating for “fact-free” journalism shows just how low discourse on this subject has sunk.

  15. Posted February 18, 2010 at 11:29 pm | Permalink

    Still waiting…oh dear…

    How about discussing this…a 95% significant level means that we can expect one finding out of 20 to be “occurring purely by chance”. Is that a low enough probability? Says who? If it is…why the T-shirt about p<.001 then? When would one threshold apply, when would the other?

  16. Posted February 18, 2010 at 11:33 pm | Permalink

    About Schmidt…if I were a warmist myself I’d disconnect his PC from the web and get everything he writes for the world vetted by somebody with a minimum of debating skills. Content is nothing when the style is so awful.

    (reminds me of myself at soccer. I am so bad at it, I end up being the “12th player” for the opposing team…)

  17. Posted February 19, 2010 at 7:04 am | Permalink

    Maurizio: I didn’t use the T-shirt photo because of the “p< .001.” I simply thought it would attract attention to the post — and it obviously worked in your case. ;-)

    Of course you are right — there is a one-in-twenty chance of the result being due to chance. You can decide for yourself how you want to spin that probability. But one thing it does NOT mean is “there has been no warming since 1995.” Which was the point of my post.

  18. Posted February 19, 2010 at 9:55 am | Permalink

    Topic for a possible future post then…is the 95% significance level enough and why…

    Because after all we could state that there has been warming since 1995, at the 90% level, could we not? 8-)

    ps personally, in a scientific endeavor like climatology I’d say the 95% sounds like the bare minimum to provide a hint, and I’d rather go for the 99% level or more to establish actual trust. Out of curiosity, what temporal interval is needed to establish that there has been warming at the 99% level? (just asking…)

  19. Posted February 19, 2010 at 10:12 am | Permalink

    Maurizio: I’m not a scientist — I am a science journalist and a journalism professor. So I probably should not try to answer your question about what specific time frame is needed to establish that there has been warming at the 99% significance level. Suffice it to say that in his interview, Phil Jones said that the shorter the time interval, the lower the significance level. Also, every climate scientist I have interviewed on this subject has said that you need at least two decades to confidently establish a trend. But that is a general answer to a specific question, and I’m afraid you’re going to have to ask someone who has more authority to speak on this issue than I do.

    But I hope you do understand my point: Marc Morano claimed that Phil Jones had said that there had been no warming since 1995. Jones absolutely positively said no such thing. And my overarching point here is that in the political sphere, these scientific questions are discussed simplistically in terms of absolutes: it is warming, or it is not warming; we’re going to hell in a hand basket, or we are not. But science actually doesn’t deal in absolutes.

    As I said in my post, in science, the 95% confidence level is generally accepted as a minimum for “good enough to be believed.” I’ll add that in some fields, such as biomedicine, that is not nearly good enough. That’s because risk = probability X consequences. So even if there is “just” a 5% risk that a new drug will kill someone, the consequences are catastrophic, creating a very high level of risk. In human health, most people would agree that such a level of risk is too high, therefore requiring a higher significance level before we can feel confident enough that a drug is safe.

    What I wrote about in this post is something very different: How sure are scientists that warming occurred during a cherry-picked interval of time (1995-2009)? The case for AGW does not depend on the answer to this specific question (let alone someone’s life). But I’ll leave it for you to decide, based on your own reading of the issue and your values, what to make of the information, and its much broader context.

  20. Eric Steig
    Posted February 20, 2010 at 8:20 am | Permalink

    Tom,

    I understand your frustration with RealClimate’s apparent mischaracterization of what you meant to say. But Gavin was responding to what he though you were implying. And I agree with him, not least because I think much of the reporting from journalists I respect — including you — has been highly irresponsible on the ‘climategate’ scandal. When you then say ‘we should do more of this, like the U.K. press are’, it sure doesn’t sound like advocacy for responsible journalism to us.

    This isn’t ‘cherry picking’ as you suggested, and nor is it anywhere near what I would characterize as an ‘attack’. It is strong disagreement, and surely there is a place for that.

  21. Posted February 20, 2010 at 9:16 am | Permalink

    Tom,
    I have a comment in moderation that expands on points made above by Eric Steig and others, with several links (presumably the reason for the delay). The U.K. media attacks on climate science are better characterized as propaganda, rather than science or journalism.

    For now, I will note that your exposition omits the crucial step between the BBC and Morano, namely the despicable and misleading Daily Mail account by Jonathan Petre. Indeed, Morano’s headline is taken directly from that of the Mail article, and links directly to it. I presume you will amend your post accordingly and attack the Mail in the same terms as you did Morano (after all, all he did was repeat the Mails’s lie).

    Clearly, Eric Steig is correct – you need to rethink fundamentally your position on recent U.K. nespaper coverage of the IPCC and climate science, or risk being perceived as an apologist for irresponsible journalism.

  22. Posted February 21, 2010 at 12:43 pm | Permalink

    Tom

    > I probably should not try to answer your question

    Mine is not strictly a question only a scientist can answer. It should be a point of information as it concerns the past. I do believe there has been warming at the 99% significance level between, say, the LIA and today: perhaps Deep Climate or any other of your commenters will be able to provide a narrower timespan than that?

    > in the political sphere, these scientific questions are discussed simplistically

    when I was making the same point a few weeks ago (pre-Climategate) I was routinely attacked as a “denialist”. Glad to see that there is something positive that has come out of the recent brouhaha.

  23. Posted February 24, 2010 at 10:37 am | Permalink

    Earth to Tom,
    When are you going to admit that your beloved U.K. press (specifically the Daily Mail and the Daily Express) is responsible for the “no warming since 1995″ falsehood, not Morano, who was just repeating it?

    And when are you going to release my previous comment? You know, or should know by now, that the U.K. press coverage of the IPCC is relying on dubious analysis from contrarian blogs, and that at least two scientists have made accusations of manufactured quotes in the Times and Mail coverage of the various fallacious “gate” stories.

This thing has 2 Trackbacks

  1. Posted February 15, 2010 at 8:28 am | Permalink

    [...] Jones: Warming since 1995 not statistically significant [Via CEJournal] [...]

  2. Posted February 17, 2010 at 7:02 am | Permalink

    [...] point is well explained in this short article from the Center for Environmental Journalism see (Jones: Warming since 1995 not statistically significant): “In an interview with the BBC, Phil Jones, the embattled director of the British Climatic [...]

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