Do The Continents Affect Surface Air Temperature?

The internet has enabled researchers and organisations of various kinds to make their data available for free to download and hence anyone with a computer and some rudimentary R knowledge can observe and analyse all sorts of trends in everything from economics to society to natural phenomena. Obviously this can provide endless hours of fun and distraction!

One such data set, available at Willmott, Matsuura, and Collaborators’ Global Climate Resource Page is a dataset that was compiled by Legates and Willmott and described in their paper [1].

This dataset is a set of estimated mean monthly surface air temperature values for various (points on a 0.5 by 0.5 degree grid) geographical locations and was made from 17986 land weather stations (most densely concentrated in the United States and Europe) and 6955 ocean recorded points. These observations came from various sources and span a period of sixty years, and were used to estimate and interpolate the temperature at various points. To give you an idea of how much data was collected, here is a map from their paper [1] showing the location of the stations (I figure showing this map is fair use):


The details of the estimations are documented in the paper, and estimated errors are also available on the website above. Although there are some pictures in the paper, they are in black and white and I thought it would be fun to make some in colour.

First, by choosing dark blue for the coolest temperature (-71.7C) and red for the warmest (40.2C), each geographical location can be plotted with the estimated mean monthly temperature for that point as a colour on the spectrum from the darkest blue to red. Here is what it looks like for January (latitude and longitude are in degrees):


Hey look! You can see the outlines of the continents. Note that I did not add in any way anything to the plot! Now, since we have twelve months, let’s make an animation:


Obviously there is much more I could have done with this dataset (plotting temperature versus latitude or longitude also looks pretty awesome!), but I hope this short post has encouraged the reader to explore all this awesome free data on the internet to learn about the world from primary sources, instead of consulting secondary sources.

[1] Legates, David R., and Cort J. Willmott. “Mean seasonal and spatial variability in global surface air temperature.” Theoretical and Applied Climatology 41.1-2 (1990): 11-21.

The plots in this post were made with R and the animation was made with ImageMagick, since the GIMP seems to have problems with my PNG files, and ImageMagick is much easier to use for animated GIF files.

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