The Temperature Of The UK Over The Last 100 Years (part 2)

A butcher's at daily maxima and minima over the last 100 years. Are things getting worse, and what does ‘worse’ mean?

I am now looking at an Excel spreadsheet of all the data I could squeeze out of this handy Met Office online resource. If any paying subscriber would like a copy please do ask - I’d like to think I’m delivering decent value for money!

Introducing Tmax

Tmax is where we shall start, this being defined as:

Just to make sure everyone understands how Tmax comes about, the absolute maximum temperature at each station is noted on a daily basis and at the end of every month somebody calculates the arithmetical mean (a.k.a. average) of these readings. Tmax is thus not a data record of the hottest temperatures recorded at each station and, if I am being honest, these are rather silly things to announce to the general public unless you are dead keen on climate propaganda.

There are several reasons for this silliness starting with the analytical reality that extremes of any kind are regarded as outliers by statisticians who will throw them away and/or replace them with interpolated, modelled or smoothed estimates. Then there’s the technical reality of a new record being held for less than a minute (depending on the sampling resolution and automated quality control procedure). Then there’s the comic reality of somebody doing something unusual in the vicinity of the Stevenson screen, like parking an ice cream van. Then there’s the surreal reality of putting your thermometer somewhere truly stupid:

By taking the average of several measures of maximum daily temperature at a specific location we iron out the effects of outliers generated by ice cream vans, venting greenhouses and other such sources of localised heat so we may start to guess what the weather is actually doing. This approach will yield better stats but it doesn’t really cut the mustard when it comes to the business of producing scary news headlines.

One other thing to bear in mind is that we can continue to log record daily temperatures on a cooling planet. This will come about if climate variability is on the increase whilst temperatures are decreasing. Statisticians give this a fancy word that comes in handy at drinks parties, this word being heteroscedasticity. Check out this Wiki entry, then try slipping in something like, “apparently, it’s all down to heteroscedasticity and not our SUV, darling” over canapés.

In sum, the mean daily maximum temperature a.k.a Tmax is a jolly decent sort that paints a truer picture than the Met-bod on the TV with the scary red and black heat maps.