Lab: Globally-Averaged Temperature

I. Introduction

Since the 19th Century, surface weather stations have recorded temperatures at various locations around the world. Only the land portions of the globe are sampled in this way, and the density of stations is greatest in the industrialized nations. Since about 1867, the number and distribution of stations has been large enough to provide an adequate (though not perfect; the sampling error is about 0.07 °C) sample of global surface temperature variations from year to year. This record provides the best documentation of recent global climate change and is at the center of the debate over humankind's potential to modify Earth's climate. Satellites, with their global coverage, have been recording a truer estimate of global temperature (in the lower troposphere, not at the Earth's surface) in recent years. However, satellite data exist only since 1980 and are not included in this lab.

In this lab you will analyze the global temperature record from 1867 to the present. You will evaluate long-term trends and shorter-term fluctuations, and you will look for evidence of the impact of climate forcings and mechanisms of natural variability on the global surface temperature. The ultimate goal is to give you a sense of the difficulties encountered in trying to extrapolate recent temperature trends into the future, and the need for models to make reasoned predictions of temperature change.

II. Lab Instructions

A. Fluctuations of the global climate

Transfer the Globally Averaged Temperature file to Excel, save it as an Excel file, and examine the contents. The data are saved in columns, with the year in column 1, monthly temperatures (in degrees C) in columns 2-13, annual mean temperature in column 14, and seasonal mean temperatures in columns 15-18 (e.g., DJF = December-January-February, which is the climatological definition of Northern Hemisphere winter).

Task 1: Choose 10 non-successive years at random, and compare the annual temperature in each year to that in the following year (e.g., if 1871 and 1925 are 2 of your 10 years, compare 1871 to 1872, 1925 to 1926, and so on).

Task 2: Make a scatter plot of DJF temperature vs. JJA temperature (do not plot either one vs. time). Add a linear trendline to the data and display the R2 value under the legend. Do especially warm winters tend to be followed by especially warm or cold summers? (Of course, DJF is only winter in the Northern Hemisphere; the issue we are exploring is whether global climate can be predicted 6 months in advance.) This plot is a perspective spanning much more than a human lifetime; our personal perception of climate change in our daily lives tends to be based on our experiences over only the last few years. Now plot the data for the 1990-2001 only; is the correlation strong or weak? Again, add a trendline and R2 to the plot.

B. Decadal-to-century variability and trends.

Task 3: Make a chart of annual temperature vs. time for the years 1867-2006 and calculate its slope and intercept.

Now make a chart of annual temperature vs. time for only the years 1975-2006. How does the slope compare to the 1867-2006 curve?

C. Interannual Variability.

Following is a list of major volcanic eruptions since 1867 and the year that each occurred:

    1883 Krakatau

    1890 Unidentified

    1902 Soufriere/Pelee

    1902 Santa Maria

    1912 Katmai

    1963 Agung

    1968 Fernandina Island

    1982 El Chichon

    1991 Pinatubo

Task 4: For any three of the above eruptions, note the average annual global temperature for the year in which the eruption occurred, the year before the eruption, the year after the eruption, two years after the eruption, and three years after the eruption. What is the typical magnitude and sign (warming or cooling) of the effect of volcanoes on global climate? How long does it take for the climate to return to normal after a major eruption?

Following is a list of El Niño years in recent times: 1951, 1953, 1957, 1963, 1965, 1969, 1973, 1977, 1983, 1987, 1991, 1997-1998, 2002-2003, 2006-2007. (For El Niño events starting near Christmas time, the following year is listed, since that is when the peak temperature anomaly usually occurs.)

Task 5: Choose three El Niño events (not ones that occurred during the year of a major volcanic eruption). Note the average annual global temperature for the ENSO year, for the year before the ENSO, and for the year after the ENSO.

D. Regional Change:

Task 6: Go to the GISS website. Given the dataset options available to you, decide which data set you should observe to determine the two warmest years on record. Be sure to include which data set you observed and what you observed in your results.

Task 7: Next, click on the "Global Maps" dataset to observe the regional surface temperature distribution for each of the two years you found above. Before you make each map, be sure that you have selected all of the appropriate parameters. Your map type should be "anomalies," your mean period should be "annual," and your time interval should span the chosen year. NB: if oceans are set to "none," you will not be able to see data for the ocean.

III. Lab Report Instructions

Write lab report (as per the Lab Report Format) summarizing the major findings of your investigation. Consider the following questions as you write your report.

IV. Optional Reading List

Excel Help - If you are unfamiliar with Excel, work through these Excel help pages.

Contributor:

Robert B. Schmunk, NASA / Goddard Institute for Space Studies, New York, NY

Last update: Spring 2007.

Updated August 24, 2007
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