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US Drought & The AMO

September 17, 2013
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By Paul Homewood


John Ashton – Climate Diplomat


I return again to the subject of the last year’s US drought . The reason will become apparent.


John Ashton, a career diplomat, and described as “one of the world’s top climate diplomats”, gave a lecture at the Tyndall Centre, in the University of East Anglia, last week, entitled “Knowledge, Power and Will in the Response to Climate Change”.

He gave us his vision of our future:-


We need, within not much more than a generation, to build an energy system that is pretty much carbon neutral. Think of that as a “4+1” prospectus.

One: a carbon neutral electricity system. No more coal or gas for electricity, unless we lock away the resulting carbon emissions through carbon capture and storage.

Two: carbon neutral transport. No more liquid hydrocarbon fuels, at least of mineral origin, for vehicles, trains, ships and eventually planes.

Three: no more gas to heat our homes and buildings.

Four: carbon capture and storage with all those processes that are inherently carbon intensive: steel and other metals, petrochemicals and plastics, cement and so on.

That’s all on the supply side of the economy. In addition – the “+1” – we will find this transition much easier if we act just as decisively on the demand side, by using energy in whatever form less wastefully than we do now.


There was plenty of talk of catastrophic rises in temperature, low carbon economies and how political change could be accomplished, which was really the purpose of the lecture. But, when searching for examples of climate change, he could only find this to say:-

Events like Sandy and the drought in the US have continued to remind people that the problem itself never went away.”

(See Section 66)


I will leave the topic of Sandy, because it has already been well covered. But what about the drought? Was that a symptom of global warming?


First let’s look at the precipitation statistics from NOAA.




Precipitation in 2012, while well below normal, was actually only the 18th lowest on record since 1895. Droughts in earlier decades have clearly been both more intense and longer lasting.

But this only tells part of the story. For the next part, we need to look at the Atlantic Multidecadal Oscillation, or AMO, which is a natural cycle of ocean temperatures in the North Atlantic. The cycle lasts about 60 years, and currently we are in the warm phase.

NOAA have produced a useful web page on the AMO, here, which is well worth a read. The pertinent part, that we are interested in today, concerns droughts. It has this to say:-


Recent research suggests that the AMO is related to the past occurrence of major droughts in the Midwest and the Southwest. When the AMO is in its warm phase, these droughts tend to be more frequent and/or severe (prolonged?). Vice-versa for negative AMO. Two of the most severe droughts of the 20th century occurred during the positive AMO between 1925 and 1965: The Dustbowl of the 1930s and the 1950s drought. Florida and the Pacific Northwest tend to be the opposite – warm AMO, more rainfall.


They even provide a map which shows this effect.



Red and blue colored dots represent positive and negative correlations of Northern Hemisphere summer rainfall with the AMO index. When the AMO is positive (warm Atlantic) there is less rainfall over most of the United States and northeastern South America, and more rainfall in southern Alaska, northern Europe, west Africa and Florida.


Now let’s look at how the AMO has cycled from warm to cold, and back again during the last century.




The warmer, or positive, phase can clearly be seen between about 1930 and 1960, the time of two major droughts. The AMO turned back to warm in the mid 1990’s.

Now let’s plot the 5-year running averages of CONUS precipitation alongside the AMO index. (The AMO axis is reversed – the positive, warm phase is “below the line”).




The drier years during the warm phase of the AMO between 1930 and 1960 are evident, as are the wetter years before and after. We should be expecting equally dry years now, but, if anything, precipitation is on the high side.

Of the top 20 driest years since 1901, 13 occurred during the warm phases of 1930-62 and 1996 to date.

To claim, therefore, that one year’s drought is due to climate change is self evident nonsense.



These are, of course, national precipitation figures, and maybe they are disguising regional patterns. The NOAA piece on the AMO does mention the Midwest specifically, and we know this was one of the hardest hit parts in last year’s drought. So let’s look at the precipitation trends in the corn belt there.




Again the pattern is totally apparent. During the warm AMO phase between 1930 and 1962, there were only 12 years, when rainfall was above average.



If anything is happening with the US climate, it is getting wetter. Droughts, historically, are natural, commonplace and have often been much worse than last year’s, particularly during the current phase of the AMO.

It is, of course, very easy to jump on last year’s drought as a sign of climate change, and most people are gullible enough to mop it up.

But each time you hear such claims, remember to press your red button.



  1. Mickey permalink
    September 18, 2013 3:06 pm

    Excellent post.

  2. Brian H permalink
    September 18, 2013 4:24 pm

    As a NW resident, it behooves me to point out that there is at least as much territory negatively correlated with AMO as positive. So a double hit on the Big Red Button.

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