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Why are long term mean temperatures based on 1981-2010 averages?


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Hi, this question I have wanted to pose to my local tv weather presenter, but never got round to it. 

I cannot understand why long term mean temperatures are based on averages between the period 1981-2010.

Why not 1981 - 2019? 

Why don't we incorporate the last decades averages into the statistics? 

Why is generally 1981 an important date to start, say? 

Why not 1971 - ????, 1961 to ???? etc, and why is the last decades avarages not taken into account in the avarages?

I'm hoping someone will clearly explain. 




Edited by Joe9t
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  • Location: Skirlaugh, East Yorkshire
  • Location: Skirlaugh, East Yorkshire

The most recent 30 year average ending on the first year of the current decade is always used. So until 1st January 2021, we use 1981-2010 and will then switch to the 1991-2020 average until 1st January 2031 when the next full decade of data can be used. Likewise in 2005 for example the 1971-2000 average was used.

The 1961-1990 average is often used aswell as a standard climatic norm, though is obviously becoming less relevant as time goes on.

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