ERTH 535:
Planetary Climate Change
(Spring 2018)
Summary of Discussion
about Lab Activity #1:
Seasonal Temperature Changes
Dave Dempsey
Dept. of Earth & Climate Sci.

Discussion based on plots created as part of Lab Activity #1: Seasonal Temperature Change

Questions to Ask about a Plot before You Try to Read and Interpret It

Before you begin to describe or interpret any plot of data, such as the global temperature and temperature difference plots in Lab Activity #1, there are several types of questions that you should try to answer about the plot:

Plots of Monthly Mean Surface TemperatureData (created using My World GIS software)

For the two temperature plots in Lab Activity #1, some responses (and some actual answers) to these questions would be:

Features of plots of January and July average surface temperature for a selected year (e.g., 1982):

Plots of Monthly-Average Surface Temperature
January 1982 July 1982


Plot of the Difference between Montly-Average Surface Temperatures from Different Months

It is not always easy to describe differences between plots of similar quantities, such as monthly-average surface temperatures in January and July, simply by placing them side by side. One, possibly more effective way to look for differences between them might be to make similar plots for the intervening months and animate the series of monthly plots. Another, often very powerful method is simply to subtract the values on one plot from the values in the corresponding cells on the other, and plot the difference. Lab Activity #1 does this for you, and the answers to some of the questions raised about the individual January and July plots of monthly-average surface temperature, are different:


Features of the patterns shown on plot of July minus January difference in monthly-average surface temperature (see a plot below):

Plot of July minus January temperature difference in 1987.
Red colors represent positive values (July warmer than January), blue colors represent negative value (July colder than January). White and near-white colors represent very small temperature difference between July and January.

July minus January Temperature
  Difference Plot