How the year 2024 is bringing average monthly temperature records into the 21st century

The Royal Netherlands Meteorological Institute (KNMI) publish a dataset of average monthly temperatures recorded at various weather station in the Netherlands since 1901. I took the data for the weather station at De Bilt and grouped it into three buckets - 20th century (years 1901-2000), 21st century (years 2001-2023) and 2024. If you average the monthly averages in each bucket and plot them you’ll see that 21st century is trending warmer than the 20th one1.

No surprises here I hope! Now let’s overlay the 2024 monthly averages:

While Jan’24 was your typical January (i.e. typical for 21st century), both Feb’24 and Mar’24 have broken new records. Feb’24 came 5.67ºC above the 20th century average and 3.98ºC above the 21st century average. March 2024 came 3.85ºC and 2.57ºC above the 20th and 21st century averages respectively.

Now let’s change the graph to show the maximum monthly average temperature recorded in 20th and 21st centuries - i.e. the record warmest months in each bucket:

Note how the green line (triangles) is above the blue one (circles) except in a few places.Note how the green line (triangles) is above the blue one (circles) except in a few places.

While most warmest months on record have been in the 21st century, Feb, Mar, Aug and Nov are exceptions. The records for these months were set in the 1990s and so belong to the 20th century. But now let’s throw 2024 monthly averages into the mix:

So 2024 has brought the records for Feb and Mar into the 21st century. Will we see the Aug and Nov records broken this year too?

Post prompted by an unusually warm April day in the Netherlands yesterday - the max temperature at De Bilt2 hit 24.1ºC.

  1. Each month is warmer by a different degree. For example, an average Sep is warmer by 1.06ºC, Nov by 1.82ºC. The average of change over the entire 12 month period is 1.53ºC.↩︎

  2. Why De Bilt is used as a reference weather station when talking about the weather in the Netherlands.↩︎

April 7, 2024