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350.org has posted following image on FB

341 months is a long time. If you're 28 or younger, you haven't experienced a full month of average global temperatures ever in your lifetime.

enter image description here

They are claiming that's the conclusion from NOAA Global Analysis - July 2013. However, the NOAA Global Analysis — July 2013 only mentions global average:

This marks the 341st consecutive month, since February 1985, that the global monthly temperature has been higher than the long-term average for its respective month.

  • Is broad statement by 350.org true (for everybody everywhere)? I remember multiple news such as "month X was the coldest in 1xx years" in last decade.
  • If not, would it be true if you'd only take global average over land?
  • Lastly, is the NOAA's statement quoted above accurate?
  • What do you mean by partially true under some circumstance? Like if only a few of the months weren't above average? – user5582 Aug 23 '13 at 16:16
  • @Sancho: more like for example "only if you take global monthly averages". I'm also not sure how to interpret "full month", i.e. if one day in a month is above average, this means you haven't had "a full month"? – vartec Aug 23 '13 at 16:19
  • The claim in the image is vague, but I think it's clear what sentence in the report it's based on. Are you fine with this question changing its focus to the more clearly worded sentence from the NOAA Analysis? – user5582 Aug 23 '13 at 16:22
  • I think it's roughly translatable as "there's more than the average amount of thermal energy in the atmosphere corrected for month for the 341st time in a row" – Sklivvz Aug 23 '13 at 16:24
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    It's not that surprising though: it roughly means the same as "it's getting measurably hotter", which we know. – Sklivvz Aug 23 '13 at 16:26
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What's being compared

The NOAA Global Analysis — July 2013 says:

This marks the 341st consecutive month, since February 1985, that the global monthly temperature has been higher than the long-term average for its respective month.

The "global monthly temperature" means the "combined average temperature over global land and ocean surfaces". (NOAA Global Analysis)

This page explains how the combined average temperature over global land and ocean surfaces is calculated:

The global time series is produced from the Smith and Reynolds blended land and ocean data set (Smith et al., 2008). This data set consists of monthly average temperature anomalies on a 5° x 5° grid across land and ocean surfaces. These grid boxes are then averaged to provide an average global temperature anomaly. An area-weighted scheme is used to reflect the reality that the boxes are smaller near the poles and larger near the equator. Global-average anomalies are calculated on a monthly and annual time scale. Average temperature anomalies are also available for land and ocean surfaces separately, and the Northern and Southern Hemispheres separately. The global and hemispheric anomalies are provided with respect to the period 1901-2000, the 20th century average.

I see no reason to doubt the NOAA conclusion that the global monthly temperature for the previous 341 months each was higher than the month's long-term average temperature. This is consistent with the hypothesis that the Earth is warming or has warmed.


The data

The combined mean surface temperature (°C) based on the years 1901-2000:

Jan: 12.0
Feb: 12.1
Mar: 12.7
Apr: 13.7
May: 14.8
Jun: 15.5
Jul: 15.8
Aug: 15.6
Sep: 15.0
Oct: 14.0
Nov: 12.9
Dec: 12.2

Here is the combined average temperature over global land and ocean surfaces from 1880-present, reported as units of 0.01°C change from the average global mean from 1950-1980 (14.0°C): http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts+dSST.txt

In that dataset, February 1994 was the most recent month where the average global temperature was lower than the global mean from 1950-1980.

It appears that the "long-term average for its respective month" quoted in the study is not simply the period between 1950-1980, because the claim is false if that is the case.

However, if you include a longer period of history before 1950, that pulls the "long-term average for its respective month" downward. Whether or not the question's claim is true turns on the definition of "long-term average for its respective month".

Pedantry

If you're 28 or younger, you haven't experienced a full month of average global temperatures ever in your lifetime.

Nobody has "experienced a full month of average global temperatures", ever. An global average is just an average, and it's totally consistent that the Earth itself has not experienced a full month of average global temperatures, and even more certain that no one person has experienced a full year of temperature that happens to match the global average.

  • Isn't this begging the question? The question cites the same reference given in the answer. – Larry OBrien Aug 23 '13 at 20:06
  • @LarryOBrien I saw the doubt as being about the interpretation of "monthly average", etc., so my answer just digs into the meanings of the words used and describes how NOAA arrives at the values it uses. You're correct, it would be begging the question if there is actual doubt about NOAA itself. Then, you'd need to peak at its data, or an independent source to answer this question. I can make this community wiki if you want to take a stab at expanding it to address that other possible source of doubt. – user5582 Aug 23 '13 at 20:11
  • The trouble with this question is how you define the global average. You have a lot of freedom to choose the relevant period that defines the average and different choices will give different answers. So the real crux is what is a reasonable period to choose. Just stating "above the global average" without specifying how you defined that is deceptive. – matt_black Aug 23 '13 at 20:58
  • @matt_black That's what the last part of my "Data" section mentions. I'm trying to find what NOAA used as their definition of "long term average for its respective month". That's not a problem with the question, though. – user5582 Aug 23 '13 at 21:01
  • As the question is one of definitions, I think this answer is appropriate--it provides the definition(s) used by the claim. It is an exercise, then, left to the reader, to determine whether these definitions, and thus the claim itself, are meaningful. – Flimzy Aug 24 '13 at 16:04

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