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

[Joe9t]

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. 

Thanks.

 

 

Edited November 22, 2020 by Joe9t
Mispelling

[reef]

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.

[Joe9t]

Thank you @reef, for a very clear and understandable explanation to my question. 

Thank you.