The Met Office tell us that September was the driest since records began 104 years ago. Last summer was ‘the hottest ever recorded’ in Australia. These extreme records hit the headlines implying that global warming is to blame. However just how likely is it that one extreme weather record or another will be broken due to pure chance? Barometer in today’s Spectator shows how to do the calculation and the results are surprising. I have simply extended the same argument to include Australia and the US.
In the following we consider 3 countries and their regions – The UK, US and Australia. The regions for the UK are England, Northern Ireland, Wales and Scotland. Similarly Australia has 6 states and the US has 50 states. That gives a total of 63 different regions if we also include the whole country itself.
Lets take 4 records that can be broken : hottest, coldest, wettest and driest. During a single year each record can be set yearly, monthly, or seasonally. That equates to 17 different time periods. Therefore for the UK there are a total of 5x4x17=340 records that can be set during the current year 2014. For Australia there are 6x4x17=408 records and for the US there are a staggering 51x4x17=3468 records.
Now lets assume that all weather records go back 104 years. The probability of a single record being broken in any year is simply 0.0096. So the probability the record will stand during the current year is 0.9904
What is the probability that any of the UK weather records will be broken during the current year ? That is
There is a 96.3% chance that at least one Met Office record will be broken this year in the UK!
For Australia there is a probability or 98.1% chance that a record will be broken and for the US there is a probability or essentially a 100% chance that a record will be broken!
So in 2014 we can be absolutely certain that at least one state in the US will have its hottest/coldest/driest/wettest month/season/year ever recorded! Such records are totally meaningless.