Using UK Met data from here, I noticed that Tmax for Decembers are cooling at -.45C / decade for 30 years. Thats a lot!
And then I wondered why? A theme I have returned to over and over is that hours of bright sunshine has increased because of cleaner air. Could more sunshine in December lead to cooler Decembers since clear skies can lead to colder temperatures in winter?
Guess what. Sunshine is up an average of 5.5 hours per year in December for the last 30 years. And compared to 1988 sunshine is up 80% in December. Instead of 28 hours of sunshine in December, the average is closer to 48.
Click on the graphs to enlarge.
This graph is Tmax % of normal versus Sunshine% of normal. The curved lines are the Loess curves from [R]. Data retrieved from here.
Why would sunshine be higher? Cleaner air in the UK (until China and India started to burn a lot more coal) thanks to the Clean Air Acts of 1956 and 1968.
The loess curves bottom out around 1968/1972.
UK Tmin (the average minimum temperature) has been cooling at -.336C/decade for last 15 years (as of Nov 2012).
Data retrieved from here. The graph has each monthly anomaly from the 1971-2000 average for the last 15 years.
An update to this post.
The last 60 months averaged .72C lower than the previous 60 months.
One month ago it was only .66C cooler.
An addition to this post on 5 year averages using NOAA data. This time I am using UK Met Bright Sunshine data.
1) The current 5 year period has less bright sunshine than the previous 5 year period.
2) The previous 5 year period had no large negative anomalies, and no unusual positive anomalies, yet it was the most sunshine since 1929.
3) The period from 1988 to 2008 was the longest without a -50 hour anomaly.
4) The large negative anomalies are returning to normal.
An addition to this post on 5 year averages/ But today I am using data from the UK. I had to first calculate the 1971-2000 anomalies. I started using that baseline because Canadian data that I downloaded already had the 1971-2000 normals calculated.
The last 5 years are on average .66C cooler than the previous 5 years, and .16C colder than the 5 year period before that, and also .1C colder than the period starting in the late 1980s.
As I noted in the blog post on Washington, the thing that struck me about this graph is that previous 5 years were not hotter than many, many other periods. By not hotter I mean the positive anomalies were not larger. What made the previous 5 years “warmer” was the absence of really large negative anomalies. The recent 5 year period saw the first anomaly colder than -4C since the 1980s and two colder than -2C when there had not been any in the previous 10 year period. The occasional really cold anomaly is part of climate. I wonder why they went away? And why did they come back?
You can download climate data from the UK Met here.
If you graph the difference between the median sunshine hours against the difference between the median maximum temperature (Tmax) you see sunshine on the rise and tmax on the rise.
Don’t forget to ask the AGW side whether climate variables other than CO2 have changed recently.