Lab Instructions: Globally-Averaged Temperature

Part 1. Short-term fluctuations of the global climate

  1. Transfer the Globally Averaged Temperature file to Excel, save it as a file named 'avtemp', 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).

  2. 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). What is the typical magnitude (i.e., ignoring the sign) of year-to-year global temperature changes? Of your 10 years, how many times did the temperature increase/decrease in the following year? Does it seem possible to predict whether next year is going to be warmer than this year globally?

  3. 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. Replot the data for the 1990-2001 only; is the correlation strong or weak? Again, add a trendline and R2 to the plot. Compare the slope of the two trendlines; entire series vs. the past decade. From your own observations what kind of winter (for spring semester) or summer (for fall semester) have we had this year in NYC? Can we predict with confidence what kind of summer (for spring semester) or winter (for fall semester) NYC is going to have?

Part 2. Decadal-to-century variability and trends

  1. Make a chart of annual temperature vs. time for the years 1867-1940 only. How would you describe the general appearance of this curve? Imagine you are a scientist in 1940 predicting the future by extrapolating this trend. What would you predict the current global temperature in 2001 to be? How does this prediction compare to the Earth's actual global temperature in 2001?

  2. Now make a chart of the same data but for the time period 1940-1965 instead. How would you describe its appearance? Calculate the slope and intercept of the curve for the period 1940-1965. In 1965. Based on this trend, what would you predict the temperature to be in 2001? In 1965, would you have been more worried about global warming or a return to another Ice Age?

  3. Now make a chart for the period 1966-2001. Add a trendline and answer the same questions asked above.

  4. Now make a plot using the full data series and calculate its slope and intercept. How is the trend different for the full series than for the three parts of the series you looked at previously? How much warming has occurred over the entire time series? How much warmer will Earth be in 100 years if the trends for

    1. the 1966-2001 period , and
    2. the full data series,

    are extrapolated into the future? Which prediction are you most confident of?

  5. What are the 5 warmest years in the record? The 5 coldest? Have we come anywhere close to having one of the coldest years in the record during your lifetime? How long a record is needed to see clear evidence of global warming?


Lab Report Instructions

  1. Write lab report (as per the Lab Report Format) summarizing the major findings of your investigation.

  2. Answer the following questions:

    1. Describe the major features of the global temperature time series in words so that a person not seeing the graph can qualitatively construct it on a sheet of paper based on your description. As you saw in previous weeks, carbon dioxide and other greenhouse gases have been increasing in concentration over the 20th Century. Discuss what if anything this has to do with the temperature time series you examined this week. Is CO2 a perfect global temperature predictor?

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

    3. 1883 Krakatau 1902 Santa Maria 1968 Fernandina Island
      1890 Unidentified 1912 Katmai 1982 El Chichon
      1902 Soufriere/Pelee 1963 Agung 1991 Pinatubo

      For 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?

    4. Following is a list of El Nino years in recent times: 1951, 1953, 1957, 1963, 1965, 1969, 1973, 1977, 1983, 1987, 1991, 1997-1998. (For El Nino events starting near Christmas time, the following year is listed, since that is when the peak temperature anomaly usually occurs.) Choose 5 El Nino 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. Does ENSO detectably affect the global temperature even though it is basically a tropical phenomenon? By how much and in which direction (warming or cooling)?

    5. Regional Change:

      View the temperature anomaly animation. Then view this past year's temperature distribution and the distribution for 10 years before.

      1. Locate the 5 regions where it warmed the most in the past year. How does warming in these areas compare with the global average? Why do you think that these areas warmed more than other regions? Where has it cooled? Was NYC warmer-than-average or colder-than-average this past year? What global significance can be attached to the weather events of a single year in NYC?

      2. How does the regional distribution of temperature change for 10 years ago differ from that of the past year? What do you think causes these differences?

      3. How does the regional pattern of warming that has occurred thus far compare with that predicted for the end of the next century (period 2071-2100 relative to the period 1961-1990)? See Figure 20 from the Technical Summary of the IPCC Working Group I Report, "Climate Change 2001: The Scientific Basis". (IPCC - Intergovernmental Panel on Climate Change.)

    6. Observations of temperature are not made uniformly around the globe. These maps from the IPCC Climate Change 2001: The Scientific Basis, Technical Summary, show the distribution of observations and temperature trends recorded (http://www.ipcc.ch/). How does this distribution of observations influence your confidence in assessing historical global warming, and regional trends?

      Figure 3: IPCC Climate Change 2001: The Scientific Basis, Technical SummaryAnnual temperature trends for the periods 1901 to 1999, 1910 to 1945, 1946 to 1975 and 1976 to 1999 respectively. Trends are represented by the area of the circle with red representing increases, blue representing decreases, and green little or no change. Trends were calculated from annually averaged gridded anomalies with the requirement that the calculation of annual anomalies include a minimum of 10 months of data. For the period 1901 to 1999, trends were calculated only for those grid boxes containing annual anomalies in at least 66 of the 100 years. The minimum number of years required for the shorter time periods (1910 to 1945, 1946 to 1975, and 1976 to 1999) was 24, 20, and 16 years respectively. [Based on Figure 2.9]

    7. How does your prediction for warming by 2100 (see your answer to question 7 above) compare with the modeled prediction of 1.4-5.8°C warming between 1990 and 2100 (IPCC, 2001)? What anthropogenic and natural factors could influence the amount of warming over the coming century?


Last update: 5/29/02.