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No significant warming since 1995

15 February 2010

More fruits from ClimateGate, the glasnost in climate science following the liberation of many emails and documents from the UK’s Climate Research Unit.

Q&A: Professor Phil Jones“, BBC, 13 February 2010 –BBC’s environment analyst Roger Harrabin intereviews Phil Jones, director of the Climatic Research Unit (CRU) at the University of East Anglia (UEA), which has been at the centre of the row over hacked e-mails.

Question: Do you agree that from 1995 to the present there has been no statistically-significant global warming

Dr. Jones:  Yes, but only just. I also calculated the trend for the period 1995 to 2009.  This trend (0.12C per decade) is positive, but not significant at the 95% significance level.  The positive trend is quite close to the significance level.  Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.

Question:  Do you agree that from January 2002 to the present there has been statistically significant global cooling?

Dr. Jones:  No. This period is even shorter than 1995-2009.  The trend this time is negative (-0.12C per decade), but this trend is not statistically significant.

Question:  There is a debate over whether the Medieval Warm Period (MWP) was global or not. If it were to be conclusively shown that it was a global phenomenon, would you accept that this would undermine the premise that mean surface atmospheric temperatures during the latter part of the 20th Century were unprecedented?

Dr. Jones:   There is much debate over whether the Medieval Warm Period was global in extent or not. The MWP is most clearly expressed in parts of North America, the North Atlantic and Europe and parts of Asia. For it to be global in extent the MWP would need to be seen clearly in more records from the tropical regions and the Southern Hemisphere. There are very few palaeoclimatic records for these latter two regions.  Of course, if the MWP was shown to be global in extent and as warm or warmer than today (based on an equivalent coverage over the NH and SH) then obviously the late-20th century warmth would not be unprecedented. On the other hand, if the MWP was global, but was less warm that today, then current warmth would be unprecedented.

Other articles about recent climate trends

  1. What happened to global warming?“, BBC, 9 October 2009
  2. World will ‘cool for the next decade’“, New Scientist, 9 September 2009 — Summary of forecasts about decadal cooling (e.g., “Advancing decadal-scale climate prediction in the North Atlantic sector“, Mojib Latif et al, Nature, 1 May 2008
  3. Climatologists Baffled by Global Warming Time-Out“, Der Spiegel, 19 November 2009
  4. World may not be warming, say scientists“, The Times, 14 February 2010

For more information from the FM site

To read other articles about these things, see the FM reference page on the right side menu bar, including About the FM website page. Of esp relevance to this topic:

Posts about global cooling

  1. More forecasts of a global cooling cycle, 15 July 2008
  2. Good news about global warming!, 21 October 2008
  3. One of the most interesting sources of news about science and nature!, 27 October 2008
  4. An important letter sent to the President about the danger of climate change, 21 October 2009
  5. About those headlines from the past century about global cooling…, 2 November 2009
  6. A look at global warming written in a cooler and more skeptical time, giving us a better understanding of climate science, 23 November 2009
  7. The facts about the 1970’s Global Cooling scare, 7 December 2009

Afterword

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2 Comments leave one →
  1. vimothy permalink
    15 February 2010 8:25 pm

    I dunno what to make of this. Why is this particular quote such a big deal?

    Also, your title reads “no significant warming since 1995″, which could easily be misunderstood by readers without a background in stats or quant research, who may not realise that significance has a technical definition as well as a commonly understood one. “No significant warming” could be interpreted as meaning that the evidence of the research under discussion basically shows that the earth has not warmed up over this period, when in fact it shows that it has, but that this finding is not significant at whatever level (they don’t seem to specify).

    You’ll note that BBC piece quotes as a finding the period 1975-2009, which does indeed show a rise in temperatures, and that this is statistically significant. (For the benefits of your reader: a commonly used boundary is 5%, so a result is “significant” if p < 0.05, where p = P(Rejecting H0|H0), or the chance of observing a test statistic at least as extreme as that observed, if the results were distributed as in the null hypothesis). So the earth "warmed significantly" during 75-09, but not during 95-09. It doesn't make sense if you think "warmed significantly" just means heated up to any meaningful degree; but that's because it doesn't–it just means that n (sample size) is smaller for the latter period, and so its harder to generate a "significant" result.
    .
    .
    FM reply: This is significant as a major change in Dr. Jones message from the previous confident forecasts of imminent doom.
    * It’s significant in light of the reports of accellerated warming, now revealed as false.
    * It’s significant that warming has slowed to a near stop, with NASA scientist James Hansen warning in January 2009 of only “4 years to save the Earth” (source), and Prince Charles warning the Copenhagen conference that “our planet has reached a point of crisis and we have only seven years before we lose the levers of control.” (source)
    * It’s significant that this is the best they can do with the obvious and large-scale manipulations of the surface temperature record (e.g., adjustments larger than the revealed “signal”, massive pruning of the number of stations).

    It’s significant as an indicator of what we’ll find when their data and methods are fully exposed to examination, despite these scientists decade-long battle to keep their secrets. I suspect that we’ll find that they had good reason to keep this information secret. And that we’ll see a different picture of global climate trends.

    An analogy is during the Clinton Presidency we’d get an explanation. When that was proved false, we’d get another — with the previous story declarerd “inoperative.” At the end we might not know the truth, but the chaning strories themselves conveyed valuable information. This was denied by their supporters, who would grasp tightly to the new story and display amnesia about the preivous versions.

    Like

  2. annie permalink
    15 February 2010 11:15 pm

    “Few paleoclimatic records from the tropical regions and the Southern Hemisphere ”
    I’d have thought from archeology – such as sediments , artifacts , pollen – there were some bits and pieces . Eg Green Sahara theory , 4,000 yrs ago .
    .
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    FM reply: There is a vast body of evidence (I have a link to a collection, which I cannot find now), which has largely gone down the memory hole. It is relatively small vs. that for the northern hemisphere.

    Like

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