Why 2012 Weather Was Not As Extreme As NOAA Say

By Paul Homewood

 

http://www.ncdc.noaa.gov/sotc/national/2012/13

 

I make no apologies for returning to the topic of last year’s weather in the USA, which NOAA gleefully declared to be the “second most extreme year on record”. (1998 was tops).

In my previous post, I raised several questions about the relevance and validity of the indices used by NOAA, which they used to come to their conclusion, not least the assumption that “mild winters were extreme”. I also presented an alternative index, which, in my view, was more realistic, and which concluded that the year, in fact, was pretty ordinary.

But let’s take a closer look at NOAA’s own index, and see how they have arrived at the conclusion they have. The index is plotted on the graph below, and indicates that 2012 was by far the most extreme year on record, except for 1998.

 

 

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

 

First, let’s remind ourselves that the index is built up from six indicators:-

1. 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.
2. The sum of (a) percentage of the United States with minimum temperatures much below normal and (b) percentage of the United States with minimum temperatures much above normal.
3. The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the PDSI and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.
4. Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.
5. The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.
6. The sum of squares of U.S. landfalling tropical storm and hurricane wind velocities scaled to the mean of the first five indicators.

Now let’s look at each of the six indicators.

 

 

The 2012 rankings for each plot are below:-

 

Step	Extreme Rank
1	1
2	2
3	7
4	60
5	70
6	79

 

It is the two temperature indicators that really make 2012 an “extreme” year in the overall index. The PDSI indicator (Step 3) is also a contributor, but, of course, this is also partly based on temperature.

 

Temperature Indicators

So let’s now look closer at the temperature indices. Why have NOAA included two, one for maximum (i.e daytime) and one for minimum (night time)? Inclusion of both simply biases the overall index in favour of warmer or colder weather than normal, and detracts from the importance of the other indicators.

I have run the NOAA indices without Step 2 (minimum temps), and the overall index now looks like this.

 

 

Suddenly, from being ranked the second most extreme year, 2012 drops to 5th place behind 1934, 1954, 2005 and 1998. Somehow, 5th place, or a one in 20 year event, does not have the same ring!

Even though 2012 was undoubtedly warm, to what degree does this make it “extreme”. Certainly, heatwaves should tightly be regarded as extreme, but is there any evidence that these were unprecedented in 2012?

A look at the four seasonal indices for maximum temperatures suggests not.

 

 

The only season which was truly exceptional in 2012 was the Spring. It was the fact that all four seasons were above normal that gave the year its top ranking.

Interestingly, the summer of 1936 was comparable with last year,with a higher index than even 1934. Yet, whereas 1934 had a mild winter, 1936 had a cold one. As a result the annual figures suggest 1936 was “normal” in comparison with 1934, as the figures below show:-

 

Year	Extreme Index % – Max Temp
1934	62.4%
1936	8.7%

 

I think this example illustrates just how misleading the whole index really is.

 

Conclusions

It is hard to avoid the conclusion that the index has been deliberately set up by NOAA as a way of making warm years appear “extreme”.

It is without question that most people, who read the “Second Most Extreme” headline, will immediately associate this with hurricanes, tornadoes, floods, droughts etc, (helped by the NOAA map at the top!). Those who do make this mistake will have been deliberately misled by NOAA.

According to Jane Lubchenko, NOAA administrator,

Scientific integrity is at the core of producing and using good science. By being open and honest about our science, we build understanding and trust.

Sorry, Jane. We don’t believe you.

 

 

 

References

Full details on the US Climate Extremes Index – http://www.ncdc.noaa.gov/extremes/cei/graph/1/01-12