Tuesday, November 24, 2009

What "hiding the decline" really looks like

The week's big global warming news continues to be "hackergate" - emails stolen from a few climate scientists that purport to reveal a global science conspiracy. The most talked-about email continues to be Dr. Phil Jones's (of the UK's Met Office) containing this sentence:

I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) amd [sic] from1961 for Keith’s to hide the decline.

Skeptics jumped on the quote as the "smoking gun" - proof scientists were altering data to show warming. But as always, their rush to judgment was premature, and as more evidence came to light, it quickly became apparent that the "trick" was completely innoucuous: Dr. Jones had simply tacked the instrumental temperature record onto the end of a reconstruction based on tree rings. Skeptical Science has the best explanation of why this trick is necessary:
"Mike's Nature trick" refers to the paper Global-scale temperature patterns and climate forcing over the past six centuries (Mann 1998), published in Nature by lead author Michael Mann. The "trick" is the technique of plotting recent instrumental data along with the reconstructed data. This places recent global warming trends in the context of temperature changes over longer time scales.
The "decline" refers to the "divergence problem". This is where tree ring proxies diverge from modern instrumental temperature records after 1960. The divergence problem is discussed as early as 1998, suggesting a change in the sensitivity of tree growth to temperature in recent decades (Briffa 1998). It is also examined more recently in Wilmking 2008 which explores techniques in eliminating the divergence problem. So when you look at Phil Jone's email in the context of the science discussed, it is not the schemings of a climate conspiracy but technical discussions of data handling techniques available in the peer reviewed literature.

But let's give skeptics the benefit of the doubt, and assume Dr. Jones was nefariously altering data. We'll throw out his dataset and use NASA's (which is more accurate anyway), starting in 2000 (2 months after Dr. Jones wrote his email). Here's what the "decline" looks like:

Here's another way of looking at it, showing that global temperatures were 0.23 degrees warmer over the 10 years after Jones wrote the email than the 10 years before:

So even if you grant skeptics' most wild-eyed accusations, the datasets Dr. Jones had nothing to do with confirm that temperatures continue to rise - most of all in the Arctic.

In fact, what's interesting is that the British data which were hacked show LESS warming over recent years than NASA's. If British scientists are altering data to "hide the decline," they aren't doing a very good job.

And yet this is unlikely to make skeptics more skeptical of their climate conspiracies. What is it about global warming that inspires such passion among the conspiracy theorists? More on that to come.


Hackers, health care, and hot air: should we protect "climochondriacs" from too much information on the web?


  1. Don't you get it? If there's a divergence problem for unknown reasons now, who's to say there haven't been similar disconnects between actual temps and dendro data in the past? The dendro record will not be a reliable way to determine temperature trends until this divergence thingy is nailed down. Which means that political decisions based partly on dendro versions of past climates (unprecedented!)are as likely to harm us as help us.


  2. Lou - you're right, dendro records only constitute *part* of our understanding of the climate. We also have reconstructions based on ice cores and corals (see here: http://www.ncdc.noaa.gov/paleo/recons.html).

    And paleoclimatology is only a small part of our understanding of climate change. We know that CO2 --> rising temps, and CO2 levels are unprecedented in the past 800,000 years (and probably 15 million). Therefore, even if we can't be certain what past temperatures were, we can be fairly sure that we've got some pretty big ones in store in our near future. I've added a couple of "related links" to the post that explain this logic.

    Also, we can't wait for 100% certainty to make decisions. I'll have something up on that subject in the next few days.

  3. The divergence problem is suggesting a change in the sensitivity of tree growth to carbon dioxide levels. This is a negative climate feedback promoting stability.


  4. You are on record as saying: "climate scientists shouldn’t be forced to make their data public".

    That statement renders your whole blog and likely your whole current self-image, mute. Sorry but you have exited the debate.

    Here is the TYPE of adjustments the lay public fails to "understand":




    If they would EXPLAIN at all there might *be* an explanation to misunderstand.

    But there is no explanation offered.

  5. Nik - you're half right. In the context of my comment, what I'm saying is, "If politically-motivated people are going to misinterpret scientists' work, then they should not be forced to make their data public." The links you provide (well, the second one at least) reinforce this point.

    Link #1: I'm not a computer programmer, so I'm not going to try and interpret the code. However, my inclination is to trust the scientist's motives instead of a random guy on the internet alleging misconduct (and no, the irony of me attacking the credibility of "random guy on the internet" is not lost on me.)

    Link #2: This one is clearly a misinterpretation. The data show tree ring reconstructions, and illustrate the "divergence" problem. Has nothing to do with altering data. Here's a good post on the topic:

    Link #3: I don't have the math background to say anything substantive about McIntyre's post. However, it does seem like evidence of climate scientists cooperating with a skeptic and making their data available.

  6. Why do you "trust the scientist's motives"?

    Are they not people, with the same biases, frailties, prejudices, responsiveness to incentive, etc. as the rest of us?

    If your career future, prestige, economic well-being etc. all depended on something, is it not possible, if only subconsciously, that you would do things to protect them?

    Are you assuming that scientists are not influenced by such mundane psychological forces?

    That somehow they (sui generis, apparently) can block out all of this normal concern for their life and ego and act solely in perfect accordance with scrupulous ethics?

  7. Yes, everyone suffers from "biases, frailties, prejudices, responsiveness to incentive, etc."

    But if these affect all people equally, why would you trust a biased layperson over a biased scientist?

    In any case, all the incentives, whether desire for money or for fame, should be leading scientists to abandon the consensus. I work in sales and marketing, and we understand that an undifferentiated product is not profitable. Likewise, agreeing with other scientists does not help you sell books or make your name stand out from the crowd. Check out my post here:

  8. Wag makes a good point here. It's the VERY few professional deniers that having been making
    a rumble on the "fame and fortune" front. The overwhelming majority of professional climate scientists have a career whether or not climate change is serious or not.

    This is like arguing that American historians are all basing their careers on the fact that Booth shot Lincoln and if something else turns out to be true, they've all lost their jobs. Ridiculous.

  9. mikeclarke - I like the analogy to historians and Booth.

    As far as professional deniers go, it's telling to see Anthony Watts dedicate entire posts to his hit count - if he stopped spouting denial, his loyal Pavlov dogs would stop coming back.

  10. he dendro record will not be a reliable way to determine temperature trends until this divergence thingy is nailed down ... thats all for a moment ..