{"id":375996,"date":"2025-04-21T11:32:43","date_gmt":"2025-04-21T09:32:43","guid":{"rendered":"https:\/\/climatescience.press\/?p=375996"},"modified":"2025-04-21T11:32:45","modified_gmt":"2025-04-21T09:32:45","slug":"is-arctic-amplification-an-averaging-error","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=375996","title":{"rendered":"Is Arctic Amplification an Averaging Error?"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

<\/p>\n\n\n\n

From Watts Up With That?<\/a><\/p>\n\n\n\n

Guest Essay by Kip Hansen<\/a><\/p>\n\n\n\n

Looking over one of my earlier essays, I found a note pointing to a very interesting journal paper whose findings raised an important question.  The paper is not new, it is almost a  decade old:  \u201cSpatiotemporal Divergence of the Warming Hiatus over Land Based on Different Definitions of Mean Temperature<\/a>\u201d; Zhou & Wang (2016) [ pdf here<\/a> ].<\/p>\n\n\n\n

The paper was looking into this issue, as stated in the introduction:<\/p>\n\n\n\n

\u201cDespite the ongoing increase in atmospheric greenhouse gases, the global mean surface temperature (GMST) has remained rather steady and has even decreased in the central and eastern Pacific since 1983. This cooling trend is referred to as the global \u2018<\/em>warming hiatus<\/em><\/a>\u2019.\u201d<\/em><\/p>\n\n\n\n

We can see what they were concerned about with in this graph:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

That is not the issue I am discussing in this essay, but I am basing this on the same study by Zhou and Wang.<\/p>\n\n\n\n

In their discussion,  Zhou and Wang say this:<\/p>\n\n\n\n

\u201cMost of the existing studies were based on global analyses of Ta<\/sub> <\/em>[elsewhere referred to as Tavg<\/sub> \u2013 kh], including those performed by several groups, such as the National Oceanic and Atmospheric Administration\u2019s (NOAA) National Climatic Data Center (NCDC) with the Global Historical Climatology Network (GHCN, the Goddard Institute for Space Studies (GISS), and a joint effort between the Met Office Hadley Center and the University of East Anglia Climate Research Unit with Temperature, version 4 (CRUTEM4).  All of the global temperature analyses for climate detection and attribution over land performed by the aforementioned groups relied heavily on T2<\/sub>.\u201d<\/em><\/p>\n\n\n\n

T2 <\/sub>is defined as \u201cthe average of daily minimum and maximum temperatures\u201d<\/em>.    To be clear, virtually all the global temperature analyses rely on that metric  T2 <\/sub> <\/strong>[ sometimes called Tavg<\/sub>].<\/p>\n\n\n\n

An alternate to T2<\/sub> is T24<\/sub><\/strong> <\/sub> \u2014 \u201cT24<\/sub> was calculated from the integral <\/em>[meaning, arithm<\/a>e<\/a>tic average<\/a> \u2013 kh] of the continuous temperature measurements, i.e., 24 hourly temperature measurements from midnight to midnight local time.\u201d<\/em><\/p>\n\n\n\n

The author\u2019s find that:<\/p>\n\n\n\n

\u201cHowever, the warming rates of T2<\/sub> and T24<\/sub> are significantly different at regional and seasonal scales because T2 only samples air temperature twice daily and cannot accurately reflect land-atmosphere and incoming radiation variations in the temperature diurnal cycle.\u201d<\/em><\/p>\n\n\n\n

Warming rates were found to be significantly different, regionally  and <\/em>seasonally, based on the method<\/strong> of determining the Daily Average Temperature<\/strong> for each weather station, further blended in by whatever processes to achieve a metric called Global Mean Surface Temperature (many different versions:  Land, Land and Sea, various gridding, etc)   or any of its regional siblings. <\/p>\n\n\n\n

Now, regular readers will recall that I have mentioned before that Tavg <\/sub> (called T2 <\/sub> in this paper because  it is the average daily temperature  found by averaging only 2 temperatures, the daily high, Tmax<\/sub>, and the daily low, Tmin<\/sub>) is not really the daily average temperature at all.<\/a>  Strictly it can be considered the Daily Median Temperature (considering the available data set as having only the two values, Max (high)  and Min (low))  or the \u201cMean of the High and Low for the day\u201d \u2013 neither of those are a proper average of the temperatures for a location (say, a weather station) for a 24 hour period.<\/p>\n\n\n\n

Zhou and Wang correctly state that T2<\/sub> or Tavg<\/sub> \u201ccannot accurately reflect land-atmosphere and incoming radiation variations in the temperature diurnal cycle.\u201d<\/em><\/p>\n\n\n\n

So what is the difference that Zhou and Wang found? <\/p>\n\n\n\n

\u201cThe trend has a standard deviation of 0.43 \u00b0C\/decade for T2 and 0.41 \u00b0C\/decade for T24, and 0.38 \u00b0C\/decade for their trend difference in 5\u00b0 \u00d7 5\u00b0 grids. The use of T2 amplifies the regional contrasts of the warming rate, i.e., the trend underestimation in the US and overestimation at high latitudes by T2.\u201d<\/em><\/p>\n\n\n\n

The method for determining Daily Average Temperatures in all the major GMST data sets has always generally been T2<\/sub>, mostly to maintain consistency with older records, which are available only as Tmin<\/sub> and Tmax<\/sub>.<\/p>\n\n\n\n

From the paper:<\/p>\n\n\n\n

\u201cFor a global average (with incomplete coverage), T2 has an important error of annual trend (0.027 \u00b0C\/decade) with respect to T24 (0.002 \u00b0C\/decade) during the period 1998\u20132013 (Table 1).\u201d<\/em><\/p>\n\n\n\n

That comes out to be a 0.025\u00b0C\/decade difference. <\/em><\/strong><\/p>\n\n\n\n

That may not be a lot \u2013 but in 50 years, that\u2019s 0.125\u00b0C.<\/em><\/p>\n\n\n\n

But Zhou and Wang definitely find that the averaging method used for Daily Average Temperature,  and thus all GSMT(land)<\/sub>, may be responsible for some of the seemingly higher rates of warming seen in our GSMT(land)<\/sub> graphs from the various groups. <\/p>\n\n\n\n

They find specifically that warming rate suffers an \u201coverestimation at high latitudes by T2<\/sub>.\u201d<\/strong><\/p>\n\n\n\n

This is what we often see from NASA:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

Let\u2019s see what Zhou and Wang found:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

The above shows\u00a0temperature trends per decade<\/em>, warming and cooling by colored dots. I have put yellow boxes around the higher latitudes in the north.\u00a0 Using T2\u00a0<\/sub>\u00a0is on the left, and T24<\/sub>\u00a0on the right.\u00a0 Far fewer red dots show when using T24<\/sub>.\u00a0\u00a0 What is missing is the great\u00a0Polar or Arctic Amplification<\/a>.\u00a0 There are warming spots in the north using T24\u00a0<\/sub>but not nearly as many, as clearly shown in the following which shows Annual Trends under T2<\/sub>\u00a0and T24<\/sub>.<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

The green boxes are the areas more closely investigated by Zhou and Wang.<\/p>\n\n\n\n

So, What?<\/strong><\/p>\n\n\n\n

I don\u2019t know \u2013 what you see above and what you read in Zhou and Wang (2016) is what you get here (in very truncated form).<\/p>\n\n\n\n

The the area denoted by green box A1 (Eastern Europe), the use of T2 <\/sub>instead of T24<\/sub> increases the decadal trend by 0.14\u00b0C. But in A3, the higher latitudes of the South America, the increase in decadal trend is a whopping 0.53\u00b0C . <\/p>\n\n\n\n

But what is blazeingly obvious is that using (Tmin <\/sub>+ Tmax<\/sub>)\/2 [the mean between the daily high and the daily low] as the Daily Average Temperatures [Tavg<\/sub> or T2<\/sub>] for individual stations led to a magnification of the decadal temperature trend between 1998 and 2013;  increasing the global land decadal trend by 0.0125\u00b0C\/decade.   Not that much \u2013 but for five decades, that comes up to an increase in GMST(land)<\/sub> of 0.0625, six one-hundredths of a degree C.<\/p>\n\n\n\n

And that is merely  interesting. <\/strong><\/p>\n\n\n\n

But even more interesting is that \u201cthe <\/em>T2 <\/em>trend shows a markedly higher overestimation in warm seasons (by ~57%) than in cold seasons (by ~3%) both regionally and globally<\/em>\u201d.  And the sharp faster warming in the highest northern latitudes is greatly reduced<\/em> when Daily Average Temperature is calculated using T24<\/sub>:  \u201cthe continuous temperature measurements, i.e., 24 hourly temperature measurements from midnight to midnight local time.\u201d<\/em><\/strong><\/p>\n\n\n\n

Bottom Line:<\/strong><\/p>\n\n\n\n

1.  Methods and definitions matter and can change our understanding of claimed rates of change of Global Mean Temperature. As covered in my series \u201cThe Laws of Averages<\/a>\u201d, not all averages give the same result or the same meaning.  Some averages obscure the physical facts<\/a>.<\/p>\n\n\n\n

2.  \u201c\u2026the use of T2 <\/em>may bias the temperature trend over globe and regions\u201d and \u201cthe sharp faster warming in the highest northern latitudes is greatly reduced\u201d by using T24  <\/sub>to calculate warming trends.<\/p>\n\n\n\n

3.  Zhou and Wang recommend using the Integrated Surface Database-Hourly (ISD-H, [T24])<\/a> available from NOAA.<\/p>\n\n\n\n

# # # # #<\/strong><\/p>\n\n\n\n

Author\u2019s Comment:<\/strong><\/strong><\/p>\n\n\n\n

I am not entirely sure about the impact of Zhou and Wang (2016) except the fact that I have not seen, in any of the NOAA and NASA global warming\/climate change material,  any hint that this important paper made any difference in their approaches to calculating warming trends.<\/p>\n\n\n\n

Zhou and Wang validates those of us who have railed against the T2 <\/sub>approach to daily temperatures and puts to rest the insistence of some that \u201cit doesn\u2019t make any difference\u201d because \u201cwe are looking at trends\u201d or \u201canomalies\u201d or \u201ctrends of anomalies\u201d.   <\/p>\n\n\n\n

Does it mean that the massive polar amplification seen in all the warming maps \u2013 that dark red swath across the top of the northern hemisphere \u2013 is an averaging method artifact?  <\/p>\n\n\n\n

Just maybe\u2026.some of it at least.<\/p>\n\n\n\n

Thanks for reading.<\/p>\n\n\n\n

# # # # #<\/strong><\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

\u201cDespite the ongoing increase in atmospheric greenhouse gases, the global mean surface temperature (GMST) has remained rather steady and has even decreased in the central and eastern Pacific since 1983. This cooling trend is referred to as the global \u2018warming hiatus\u2019.\u201d<\/p>\n","protected":false},"author":121246920,"featured_media":376008,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","_crdt_document":"","advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[691834641,691821957,691831096,691818288,691818087,691828892],"class_list":{"0":"post-375996","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","6":"hentry","7":"category-uncategorized","8":"tag-antarctic-amplification","9":"tag-arctic-amplification","10":"tag-global-mean-surface-temperature-gmst","11":"tag-global-temperature","12":"tag-global-warming","13":"tag-national-oceanic-and-atmospheric-administrations-noaa","15":"fallback-thumbnail"},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/04\/0gmd-12-1139-2019-f01-web.png?fit=1401%2C707&ssl=1","jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/paxLW1-1zOs","jetpack-related-posts":[{"id":385186,"url":"https:\/\/climatescience.press\/?p=385186","url_meta":{"origin":375996,"position":0},"title":"Arctic Warming Will Lead To Arctic Cooling, Recent Study Suggests","author":"uwe.roland.gross","date":"26\/06\/2025","format":false,"excerpt":"A\u00a0recent paper explains\u00a0how a weaker Atlantic Meridional Overturning Circulation (AMOC) could actually reduce Arctic warming by the end of the century\u2026","rel":"","context":"In \"Arctic\"","block_context":{"text":"Arctic","link":"https:\/\/climatescience.press\/?tag=arctic"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/06\/image-574.png?fit=1024%2C1024&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/06\/image-574.png?fit=1024%2C1024&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/06\/image-574.png?fit=1024%2C1024&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/06\/image-574.png?fit=1024%2C1024&ssl=1&resize=700%2C400 2x"},"classes":[]},{"id":274612,"url":"https:\/\/climatescience.press\/?p=274612","url_meta":{"origin":375996,"position":1},"title":"Arctic \u201cAmplification\u201d Not What You\u00a0Think","author":"uwe.roland.gross","date":"20\/08\/2023","format":false,"excerpt":"This post is challenging the notion of Arctic Amplification itself.\u00a0 The term is bandied about with the connotation that man-made global warming is multiplied in the Arctic and responsible for weather extremes.","rel":"","context":"In \"Arctic Amplification\"","block_context":{"text":"Arctic Amplification","link":"https:\/\/climatescience.press\/?tag=arctic-amplification"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/08\/0a2309-socialmedia_slp_published.webp?fit=1200%2C670&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/08\/0a2309-socialmedia_slp_published.webp?fit=1200%2C670&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/08\/0a2309-socialmedia_slp_published.webp?fit=1200%2C670&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/08\/0a2309-socialmedia_slp_published.webp?fit=1200%2C670&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/08\/0a2309-socialmedia_slp_published.webp?fit=1200%2C670&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":333430,"url":"https:\/\/climatescience.press\/?p=333430","url_meta":{"origin":375996,"position":2},"title":"The Battle of Climate Hypotheses: The Green-House Gas Forcer Vs. 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