How Extreme Was US Weather In 2012?

By Paul Homewood

 

http://www1.ncdc.noaa.gov/pub/data/cmb/images/us/2012/ann/Prelim_Significant_Weather_US2012.gif

 

According to NOAA, 2012 was the “second most extreme year on record” in the US. (The most extreme was 1998). They gleefully describe it thus:-

2012 was a historic year for extreme weather that included drought, wildfires, hurricanes and storms; however, tornado activity was below average, according to an analysis released today by NOAA’s National Climatic Data Center

(The tone is set immediately with the above map, which appears at the top of their report. As hurricanes, storms and tornadoes were near record low levels, the map, together with their opening statement, is blatantly misleading).

But just how extreme was it really? With global warming failing to materialise as planned, NOAA and others have been desperate to show that extreme weather is on the increase, and that mankind is responsible. In recent years, they have been running a “US Climate Extremes Index”, and it is this index, shown below in Figure 1, that they have based their claims around.

 

Figure 1

 

So let’s start by looking at how they define and measure extreme weather. The index is based on 6 different indicators:-

1. Daily maximum temperature.
2. Daily minimum temperature.
3. The PDSI drought index.
4. Extreme 1-day precipitation events.
5. Days with/without rainfall.
6. Landfalling tropical storms and hurricanes.

(It is worth noting that tornadoes are not included, partly because of any meaningful data before around 1970. As last year was an extremely quiet one for tornadoes, their inclusion would have made a big difference to the index. This, however, did not stop NOAA putting “TORNADOES” on their map!)

Now let’s take a closer look at these indicators.

 

1) Temperatures – extremes in maximum temperatures, (and similarly with minimums) are defined as:-

The sum of (a) percentage of the United States with maximum temperatures much below normal and (b) percentage of the United States with maximum temperatures much above normal.

This immediately creates a couple of problems.

a) According to this definition, mild winters would be classed as “extreme”, which is clearly a nonsense.

b) What is “normal”? For instance, an average of rainfall, based on the dustbowl years, would tell us that higher levels in later years were “excessive”.

The index calculates “normal” on the full record back to 1910, but in what way was weather in 1910 any more normal than weather today? Indeed, if we took recent years as the “normal”, most of the 20thC would look pretty extreme.

Most people would associate “extreme weather” with something undesirable and harmful. NOAA clearly understand this, hence their map at the top.

c) As both minimums and maximums are measured separately, it could be argued there is double counting here.

2) PDSI – As this index is essentially based on a combination of rainfall and temperature data, it is utterly superfluous, as these are already factored in.

 

3) Extreme daily rainfall – again, rainfall is factored in under 5). In any event, the lack of recording stations in earlier years must make this an unreliable indicator.

4) Days with/without rainfall – again, this is in comparison with a “normal”.

 

The graphs for each of the six indicators are shown below. It is interesting to note, that 2012 was only “extreme” on the two temperature indicators, and to a lesser extent on PDSI. (Remember, you can have severe moisture surplus, as well as drought!)

 

                                           Figures 2-7

 

 

 

http://www.ncdc.noaa.gov/extremes/cei/graph/6/01-12

 

An Alternative Look

We often hear today’s climate described as “post-normal”, but what was so normal about climate 50 or 100 years ago? The bottom line is that the climate of the last couple of decades or so is what we have all lived through, and adapted to. Bearing this fact in mind, and putting more emphasis on what most people would regard as extreme weather, I have come up with my own index, based on:-

1. Cold temperatures in winter – the colder it is, the more “extreme”.
2. Hot temperatures in summer – the hotter it is, the more “extreme”. (I appreciate Minnesota might like a warmer summer, but I have to draw the line somewhere!)
3. Annual precipitation variation, compared with the 1981-2010 mean, (both higher and lower).
4. Tropical storms/hurricanes, as calculated in NOAA’s index.

Rather than using the “percent of area affected” system that NOAA have adopted. I have chosen a ranking system. Each year since 1910 is given a ranking for each category, with “1” being the least extreme, and “103” most extreme. The four individual rankings are then averaged together, to give the overall ranking.

The results are shown in Figure 8.

 

 

 

Figure 8

2012 finishes with a ranking of 54, making it an unremarkable 46th most extreme, out of 103. The individual rankings are:-

Category	Ranking
Winter Mean Temperature	3
Summer Mean Temperature	101
Rainfall Variation	89
Hurricanes/Tropical Storms	22

 

Under my ranking system, the worst years for extreme weather were:-

Year	Comments
1936	2nd coldest winter, as well as 4th hottest summer and drought.
1933	5th worst for hurricanes, hot summer, dry.
1910	4th coldest winter, driest year on record.
1988	8th driest year, 9th hottest summer
1955	Cold winter, very dry, hurricanes.
1918	7th coldest winter, dry

 

My system does have one drawback – based on national data, regional variations could be missed. For instance, a wet East Coast could cancel out a dry West Coast! However, I think it is fair to say, that in 2012 the warm and dry weather was pretty well distributed.

 

It does not surprise me that NOAA are using methodology designed to support their agenda. But if you gave people the choice of today’s climate, or 1936’s, I suspect I know the answer you would get.

 

Footnote

If you are wondering why 1934 did not appear in the top 6, it had a very mild winter.

 

References

All temperature and rainfall data from NCDC

http://www.ncdc.noaa.gov/oa/climate/research/cag3/na.html