Global Warming: Trend and Variation

Sit on the beach and watch the tide come in.  You will see some big waves, some small.  The water's edge will advance and recede in a way that is not entirely predictable.  But there is an overall patern that emerges as the hours roll by, and the beach narrows before you.  
People get this.  Even the mathematically inept do not scurry to sunbathe higher on the beach if they see a larger wave in a receding tide.  They know the difference between trend and variation.
The difference between trend and variation can be found everywhere in our daily lives.  As this video shows, it can even be found so simple a thing as a dog being taken for a walk:
(Video by Teddy TV, presenter: Siffer, animator: Ole Christoffer Hager)
Although the distinction between trend and variation is as commonplace as an incoming tide, or a dog being taken for a walk; when it comes to climate many people seem to forget it.  They cannot find a temperature graph without seeing a trend each time the variation drifts downwards, and noise each time it goes up.   By doing so, they think they can obscure the long term trend.
Being fair, in this "dog walk" we cannot see the owner directly.  We can, however, infer his path.  It is as simple as looking for the long term trend.  So, when you try to predict likely future temperatures, are you the sort of person who looks at the dog?  Or the owner?

Posted by Tom Curtis on Saturday, 7 January, 2012

Creative Commons License The Skeptical Science website by Skeptical Science is licensed under a Creative Commons Attribution 3.0 Unported License.