By Paul Homewood

  

The UK Met Office has just published a new report on “Climate Extremes” in the UK:

 

 

https://www.metoffice.gov.uk/news/releases/2018/climate-extremes-report-supplement

 

 

It has already generated spurious headlines, such as this one from the BBC:

 

A new Met Office report says the UK has experienced more weather extremes over the last 10 years when compared to previous decades.

https://web.archive.org/web/20181102011920/https://www.bbc.co.uk/news/science-environment-46064266

 

The report says nothing of the sort, and certainly does not support the BBC’s disgraceful attempt to link it to drought, as it actually says the opposite.

Having said that, the Met Office report itself is in some ways misleading. This is their press release:

A new report by the Met Office, published today, reveals further details about changes in the UK’s climate since the 1960s. By documenting temperature and rainfall climate extremes, including periods of warmth, cold and spells of wet or dry weather, the report reveals changes in some types of extreme weather.

By comparing different meteorological reference periods, a number of interesting trends can be observed. For example, the hottest day of each year over the most recent decade (2008-2017) in the UK has been on average 0.8 °C warmer than the hottest day of each year over the period 1961-1990. Conversely, the lowest temperature of the year has shown an even greater increase, becoming 1.7 °C milder between the two periods in the UK.

This study uses a set of measures agreed around the globe by the World Meteorological Organization and World Climate Research Programme, and are widely used in global climate change research.  These metrics include at least one measure – Tropical Nights – which is currently not a common feature of the UK climate, but it could become more widespread in future. Tropical nights are defined as 24-hour periods when the minimum temperature doesn’t fall below 20.0 °C.

Dr Mark McCarthy is the head of the Met Office’s National Climate Information Centre, the team which produced the report. He said: “Monthly, seasonal and annual climate data provide a valuable record of the changing climate in the UK. However, these average figures have a tendency to mask extreme weather and climate events. So in our latest report we have focussed on those measures which record weather extremes – complementing our recently published State of the UK climate 2017 report – which shows how the UK’s climate is changing.”

Commenting on the tropical nights measure, Dr McCarthy added: “Minimum overnight temperatures of over 20.0 °C in the UK are rare currently and even during this summer this threshold was only exceeded on a few occasions. However, with projections in climate suggesting warmer temperatures, it is useful to have this metric in place, so that future changes can be monitored.”

The report summarises a set of core indices, which can be obtained from temperature and rainfall data. It also shows climate shifts for UK countries and regions, along with maps showing the data across four time periods: 1961-1990; 1981-2010; 2008-2017; and 2017.

https://www.metoffice.gov.uk/news/releases/2018/climate-extremes-report-supplement

 

Overall, the report actually confirms much of the recent GWPF report on extreme weather, “DEFRA v The Met Office”. In particular:

 

• The hottest days each year are not getting hotter.

The chart below is from the new Met Office report, and shows daily maximum temperatures in the last decade have got nowhere near those of 1975, 1976, 1990, 1995, 2003 and 2006.

 

 

• The number of “hot days” each year has been declining since the 1990s:

The report defines a “summer day” as over 25C:

According to the report, the average in the last decade has dropped to 5.3 days, from the 1981-2010 average of 6.4.

 

• Extremely cold days are much less common than in the past

 

  

• Droughts have become less frequent

 

   

 

However, certain aspects of the new report merit further questioning. In particular:

1) The hottest day of each year over the most recent decade (2008-2017) in the UK has been on average 0.8 °C warmer than the hottest day of each year over the period 1961-1990

Yet as the Met Office’s own infographic shows, the latest decade is virtually the same as the 1981-2010 average:

The convention of using the most recent three decades as the climatic norm is well established, so why does the Met Office persist in using 1961-90 as its standard reference period?

2) Tropical Nights

According to Mark McCarthy:

Minimum overnight temperatures of over 20.0 °C in the UK are rare currently and even during this summer this threshold was only exceeded on a few occasions. However, with projections in climate suggesting warmer temperatures, it is useful to have this metric in place, so that future changes can be monitored

In fact, they are so rare that they barely exist at all outside of the heavily urbanised areas of London and the West Midlands, where night temperatures are affected by UHI. Even then the incidence is about one night per decade.

The numbers are so sparse as to be meaningless statistically.

As if to emphasise this point, the highest recorded daily minimums on CET were 18.8C, set in 1948 and again in 1997.

In short, these are simply extremely rare and random weather events.

https://www.metoffice.gov.uk/hadobs/hadcet/cet_record_breakers.html

3) Wetter days?

The report appears to show that total rainfall from the wettest days, (>99th percentile), has increased since the 1960s.

However, the period from the 1960s to 90s is well known by scientists to have been a “flood poor period”, so drawing conclusions from such a short period is dangerous.

The Met Office’s own report admits that this is the case, when discussing dry spells.

It is not clear why the Met Office chose to begin their rainfall analyses in 1960, and not an earlier period which would have yielded more meaningful results.

Overall, the report confirms  that UK weather is, if anything, becoming less extreme:

• Summer days are not getting hotter
• Extremely cold days are much less common
• Droughts are less intense