A Different Take on the “Hottest Month on Record.”

Figure 1. Hottest Month on Record!!!

NCDC Releases July 2012 U.S. Monthly Climate Report: July 2012 Marked the Hottest Month on Record for the Contiguous United States.”  

The headline was, of course accompanied by nonsense like this

Senior Meteorologist Stu Ostro (Twitter) says, “Exceeding July 1936 at the peak of the Dust Bowl heat — is BIG.”

The “record” is less than 120 years long. The warmest month on record in the US, isn’t any more significant to climate change than this past weekend’s abnormally cool weather was.

NOAA’s hottest month ever is based on the homogenized US Historical Climatology Network (USHCN). THe USHCN is a subset of the GHCN…

Investigation of methods for hydroclimatic data homogenization

Steirou, E., and D. Koutsoyiannis, Investigation of methods for hydroclimatic data homogenization, European Geosciences Union General Assembly 2012, Geophysical Research Abstracts, Vol. 14, Vienna, 956-1, European Geosciences Union, 2012.

We investigate the methods used for the adjustment of inhomogeneities of temperature time series covering the last 100 years. Based on a systematic study of scientific literature, we classify and evaluate the observed inhomogeneities in historical and modern time series, as well as their adjustment methods. It turns out that these methods are mainly statistical, not well justified by experiments and are rarely supported by metadata. In many of the cases studied the proposed corrections are not even statistically significant.

From the global database GHCN-Monthly Version 2, we examine all stations containing both raw and adjusted data that satisfy certain criteria of continuity and distribution over the globe. In the United States of America, because of the large number of available stations, stations were chosen after a suitable sampling. In total we analyzed 181 stations globally. For these stations we calculated the differences between the adjusted and non-adjusted linear 100-year trends. It was found that in the two thirds of the cases, the homogenization procedure increased the positive or decreased the negative temperature trends.



This is why “U.S. temperature trends show a spurious doubling due to NOAA station siting problems and post measurement adjustments.”

Poor station siting in the USHCN is also the reason that NOAA’s new U.S. Climate Reference Network (USCRN) shows July 2012 to be 75.5°F (about 2°F cooler than the USHCN. The homogenized USHCN supports AGW by artificially cooling the past and artificially warming the present.

While there are valid technical reasons for homogenizing the older records to account for changes in methods, instruments, station location and environmental alteration around stations… The methods used to homogenize the data induce artificial warming. This is a cold, hard, empirical fact. The USHCN data used by NOAA has been artificially cooled in the past in an effort to “homogenize” the older data and methods with the modern data and methods. Remove the homogenization and July 2012 would be 1.0°F cooler than July 1936.

However, even if the homogenization is producing a more accurate temperature record, the “record” is not long enough to say much of anything about climate.

Meteorologically speaking, “climatology” refers to periods greater than 30 years long. “Normal” climatology is generally the most recent 30-yr average. The 30-yr average is climate (what you expect). July and last weekend were weather (what you get). July was significantly warmer than average. Very few months (or weekends) are “average.” Most are above or below average.

Above Normal – One of the outlook categories that are based on the 1981-2010 climatological normal. During this 30 year reference period, average three-month temperature was observed in Above Normal category (10 warmest years) 1/3 (33.3%) of the time.

Anomaly – The deviation of a measurable unit, (e.g., temperature or precipitation) in a given region over a specified period from the long-term average, often the thirty year mean, for the same region.

B – Is used on climate outlooks to indicate areas that will likely be below normal.

Below Normal – One of the outlook categories that are based on the 1981-2010 climatological normal. During this 30 year reference period, average three-month temperature was observed in Below Normal category (10 coolest years) 1/3 (33.3%) of the time.

Climate – Prevailing set of weather conditions at a place over a period of years.

Climate Change – A non-random change in climate that is measured over several decades or longer. The change may be due to natural or human-induced causes.

NOAA National Weather Service

In reality, climate is a combination of prevailing weather patterns and physical geography.  Climatological normals are the mean weather patterns during a 30-yr reference period.  Climate change occurs over “several decades or longer.”

NOAA’s NCDC trumpets warm months as all time climate records. The “hottest month on record” in the a NCDC headline is an assertion of climatic significance. When it has no more climatic significance then the coldest August 18-19 on record.  Weather records are broken all of the time.

“Climate Normals”

The current climate normals (1981-2010) were adopted on July 1, 2011…

NOAA’s 1981-2010 Climate Normals

NOAA’s National Climatic Data Center (NCDC) released the 1981-2010 Normals on July 1, 2011. Climate Normals are the latest three-decade averages of climatological variables, including temperature and precipitation. This new product replaces the 1971-2000 Normals product. Additional Normals products; such as frost/freeze dates, growing degree days, population-weighting heating and cooling degree days, and climate division and gridded normals; will be provided in a supplemental release by the end of 2011.

NOAA National Climatic Data Center

The previous climate normals were from 1971-2000.   I made an assumption that the climate normals are adjusted once per decade.  If my assumption is correct, these are the climate normals reference periods since 1931:

Decade            Reference Period Mean July Temp.  (° F)
1931-1940 1901-1930 73.79
1941-1950 1911-1940 74.51
1951-1960 1921-1950 74.59
1961-1970 1931-1960 74.73
1971-1980 1941-1970 74.23
1981-1990 1951-1980 74.35
1991-2000 1961-1990 74.33
2001-2010 1971-2000 74.38
2011-2020 1981-2010 74.76

The NOAA data are available here: NCDC CDO

It appears to me that there is nothing terribly anomalous about the current 1981-2010 reference period.  It’s 0.03° F warmer than the 1931-1960 reference period.

Here’s a plot of U.S. July temperatures (1895-2012)…

Figure 2. U.S. July temperatures (1895-2012). The open green line represents the assumed decadal climate normals.

I’m sure that the actual 2012 July temperature must have been a few 1/100ths of a degree warmer than 77.4°F; otherwise July 2012 is actually a bit cooler than July 1936, despite the homogenization.

Rather than calculate a temperature anomaly relative to a fixed reference period, I decided to calculate it against what I think the contemporaneous reference period would have been (AKA a different take).

Example: The 1931-1940 anomaly is calculated against the 1901-1930 reference period. 

Since “climate is what you expect and weather is what you get,”  the very hot year of 1936 should be measured against the contemporaneous expectation.  Here’s the July temperature anomaly with a different take…

Figure 3. A different take on the July temperature anomaly.

It’s quite evident that July 1936 was a lot hotter than July 2012, relative to what was expected (climatology).  One other thing should also be evident.  The climate normals of the 20th century did not vary a lot and the current climate normals are not anomalous.  The weather has varied a lot, the climate not so much.


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