Climate Progress: “1983-2012 was the warmest 30 years of the last 1400 years.” [Fact Checking]

January 2, 2014 11:08 am1 comment

POSTED FOR COMMENTARY BY THE CCNF SCIENTIST COMMUNITY:

Shoreline rocks and melting ice, Duluth, Minnesota, March 2013, by Joel Abroad via Flickr

Shoreline rocks and melting ice, Duluth, Minnesota, March 2013, by Joel Abroad via Flickr

“1983-2012 was the warmest 30 years of the last 1400 years.” 

http://thinkprogress.org/climate/2013/12/16/3034511/climate-bad-news-2013/

Source: “9 Reasons Why 2013 Was Not The Best Year in Human History,” by Ryan Koronowski and Kate Valentine, Dec. 16, 2013.  ThinkProgress.org.

THE FORUM'S COMMENT THREAD

  • I’ll use this claim, one I have interest in, as a vehicle to discuss how I would address it, conceptually, philosophically, in trying to determine its importance.

    The claim falls into a class of commonly seen statements following the general form “The last x [time period] has been warmer than any in the last y [longer time period]”. We can raise at least two fundamentally important questions here:
    1) Are such claims informative in terms of determining the current human impact on the climate? If not, are they useful in other ways
    2) What is the evidential basis of such claims and how valid are they?

    Relative to the first question, such statements are observational only, and as such, do not in and of themselves, provide information on cause and effect, but only help to contextualize condition states at different time points. If we take the statements as being correct, we can then move on to questions and methods that attempt to explain why. But based on strict logic, whether the recent past is warmer or colder than the more distant past is independent of what is causing an observed, recent warming. This can be understood by the simple observation that if you go back far enough in time, you will eventually find a period where it was warmer, even far warmer, than the recent past, and we would not logically conclude from that that humans are therefore not responsible for the recent warming. The two things are simply not logically related. And the converse also holds: we do not go back 1400 years, note that a recent 30 year period was warmer than any other such during that period, and conclude that humans are therefore the cause of the recent warming. They might very well be, but not because of that data. However, this is typically the implicit assumption when such statements are made, as in the ThinkProgress.org piece.

    2) The second question involves issues of scientific method: what types of evidence were used to derive this statement, and what was the inferential process used. This question immediately raises a number of sub-questions, such as (1) What geographic area is being referenced?, (2) What types of proxy material were used?, (3) How well known is the form of the relationship between proxy and temperature?, and (4) How complex is the process that generates the proxy material, and therefore, what is the likelihood that a given proxy value corresponds uniquely to a given climatic state, or range thereof? Then there are also a series of secondary questions, dealing for example with the spatial dispersion of the proxy-based estimates and other sampling related issues.

    These questions are not simple–large uncertainties are attached to several of them, depending on proxy material, time period of interest and other variables. Good science starts from taking a thorough account of these uncertainties and proceeding from that point, so as not to come to wrong conclusions. Or even to right conclusions for that matter, if those are stated with more certainty than is warranted by the available evidence.

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PUBLIC COMMENT THREAD

  • http://ecologicallyoriented.wordpress.com/ Jim Bouldin

    I’ll use this claim, one I have interest in, as a vehicle to discuss how I would address it, conceptually, philosophically, in trying to determine its importance.

    The claim falls into a class of commonly seen statements following the general form “The last x [time period] has been warmer than any in the last y [longer time period]”. We can raise at least two fundamentally important questions here:
    1) Are such claims informative in terms of determining the current human impact on the climate? If not, are they useful in other ways
    2) What is the evidential basis of such claims and how valid are they?

    Relative to the first question, such statements are observational only, and as such, do not in and of themselves, provide information on cause and effect, but only help to contextualize condition states at different time points. If we take the statements as being correct, we can then move on to questions and methods that attempt to explain why. But based on strict logic, whether the recent past is warmer or colder than the more distant past is independent of what is causing an observed, recent warming. This can be understood by the simple observation that if you go back far enough in time, you will eventually find a period where it was warmer, even far warmer, than the recent past, and we would not logically conclude from that that humans are therefore not responsible for the recent warming. The two things are simply not logically related. And the converse also holds: we do not go back 1400 years, note that a recent 30 year period was warmer than any other such during that period, and conclude that humans are therefore the cause of the recent warming. They might very well be, but not because of that data. However, this is typically the implicit assumption when such statements are made, as in the ThinkProgress.org piece.

    2) The second question involves issues of scientific method: what types of evidence were used to derive this statement, and what was the inferential process used. This question immediately raises a number of sub-questions, such as (1) What geographic area is being referenced?, (2) What types of proxy material were used?, (3) How well known is the form of the relationship between proxy and temperature?, and (4) How complex is the process that generates the proxy material, and therefore, what is the likelihood that a given proxy value corresponds uniquely to a given climatic state, or range thereof? Then there are also a series of secondary questions, dealing for example with the spatial dispersion of the proxy-based estimates and other sampling related issues.

    These questions are not simple–large uncertainties are attached to several of them, depending on proxy material, time period of interest and other variables. Good science starts from taking a thorough account of these uncertainties and proceeding from that point, so as not to come to wrong conclusions. Or even to right conclusions for that matter, if those are stated with more certainty than is warranted by the available evidence.