Exercise #1: Temperature Trends in Davis, CA

Learning Objectives

Interpret graphical representations of data
Convert between Celsius and Fahrenheit
Compare temperature data from satellites and ground stations
Explain the costs and benefits of satellite data and ground station data
Explain the purpose of using a running average
Compare running averages over different lengths of time
Examine temperature graphs to determine whether there has been climate change in Davis, CA

Summary

This exercise is paired with “Essay 1” in which students follow the instructions for the process of accessing data from NASA satellite and ground stations for a given location, and graphing that data. In this exercise you are asked to examine graphs of Davis’ average temperatures from satellite and ground stations to determine whether there has been a climate change trend. You will first explore the difference between satellite and ground station data, then examine the difference a running average makes. Lastly, you will compare the results from different running averages (5 year, 11 year, and 21 year).

References

Bloom, Arnold J (2010) Global Climate Change, Convergence of Disciplines, Sinauer Associates, Inc, Sunderland, Massachusetts.

Goddard Institute for Space Studies (2009) Global Temperature Trends: 2008 Annual Summation. http://data.giss.nasa.gov/gistemp/2008/ accessed September 22, 2012.

National Research Council (2006) Surface Temperature Reconstructions for the Last 2,000 Years , The National Academies Press, Washington, D.C., http://www.nap.edu/catalog.php?record_id=11676 accessed September 22, 2012.

NASA’s Surface meteorology and Solar Energy data http://eosweb.larc.nasa.gov/sse/ accessed September 22, 2012.

NASA's Ground station temperature data http://data.giss.nasa.gov/gistemp/station_data/ accessed September 22, 2012.

Exercise

Background

You have probably heard from many sources that the global climate is warming. In fact, global temperatures have warmed more than 0.6°C during the last century (National Research Council 2006). In particular, the year 2010, was the hottest on record, followed in descending order by 2005, 1998, 2003, 2002, 2006, 2009, 2007, 2004, 2001, and 2008 (Godard Institute of Space Studies 2011). But what does all of this mean? Where does temperature data come from and how reliable is it? There may have been some warm years recently, but does this mean there is a warming trend? A global warming trend is a prolonged period of time when global average temperatures are warmer than their historical average.

In this exercise, you will examine temperature data for Davis CA from two sources: satellite data and ground station data.

Ground Station Data:

Ground weather stations are facilities with instruments that observe and record data on many atmospheric conditions, including temperature. Reliable weather records from ground stations are available for about the past 200 years. Weather stations may not be available in regions of interest, and individual stations may lack data for long time intervals. Weather stations record variations in localized weather. Information from multiple stations can be combined to examine weather over larger geographic areas.

Satellite Data:

Weather satellites orbit the earth and make indirect measurements of temperature. They are equipped with instruments that detect visible, infrared, or microwave radiation. Measurements of radiances in those wavelengths must then be mathematically converted to obtain the temperature. The temperature record from satellites extends for about 50 years, as the first successful weather satellite was launched by NASA in 1960. Satellites measure weather on a global scale, over vast geographic areas.

Compare Satellite and Surface Temperature Records

For this assignment, you will be using the Excel spreadsheet entitled “Exercise_1_Davis_Data_and_Charts.xls.” If you are unfamiliar with the use of spreadsheets, please view the video entitled “Essay1 Walkthrough and Tips.” Note that there are multiple pages in this spreadsheet, each with a labeled tab. Click on the Davis min temp tab. The data in this table was taken from NASA’s Surface Meteorology and Solar Energy website. This table shows minimum temperatures in Davis CA during every month for each year data was recorded, as recorded by weather satellites. The second tab titled Davis max temp has a table from the same website with the maximum temperatures in Davis CA during every month for each year data was recorded.

Select the tab titled Davis satellite charts. On this page you will see graphs made using the satellite temperature data for Davis CA. For this set of questions examine only the graphs of the average temperatures and not the running averages.
1. For how many years is temperature data available?
2. From looking at the graph, can you estimate what the minimum average temperature is in February in Davis? Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).
3. Does the February minimum average temp graph appear to have any trends (warming or cooling)?
4. From looking at the graph, can you estimate what the maximum average temperature is in July in
Davis? Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).
5. How many degrees does the maximum average July temperature vary by over this time period?
Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).

Celsius to Fahrenheit

1. Multiply degrees Celsius by 9
2. Divide by 5
3. Add 32

Select the tab titled Davis ground charts. On this page you will see graphs made using the ground station temperature data for Davis CA.
1. For how many years is temperature data available?
2. From looking at the graph, can you estimate what the average temperature is in February in Davis? Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).
3. Does the February average temp graph appear to have any trends (warming or cooling)?
4. From looking at the graph, can you estimate what the average temperature is in July in Davis? Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).
5. How many degrees does the average July temperature vary by over this time period? Give your answer in degrees Celsius (C) and degrees Fahrenheit (F).

Compare the satellite and ground charts.
1. Is there more data available for the satellite data or the ground data? How much more data (how many more years)?
2. If you were trying to see if there was a climate change trend happening in Davis, which data source would you rather use and why?

Examining Trends

When you look at the graph of February Average Temperature, you probably notice that there is a lot of variation from year to year, indicated by the wiggle in the graph line. This variation can make it difficult to see trends. To smooth the data, we can do a running average. A running average takes into account the data before and after the point you are interested in. To see how this works, click on the “Davis min temp” tab. Scroll to the right, past the Year and month temperature data. You will see a table labeled “5 Year Running Average.” Click on the February 1985 cell and you can see the equation that was used to calculate this number. The 5 year running average for 1985 is the average of the combined 2 years before (1983 and 1984) and 2 years after (1986 and 1987) in addition to the temperature in 1985, for a total of 5 years. This calculation is repeated for each year. Different numbers of years can be used for the running average. On the “Davis ground charts” tab, you can see the running average temperatures for 5 years, 11 years, and 21 years.

Click on the “Davis satellite charts” tab. Here you can compare the average temperature to the 5 year running average temperature.
1. When you compare the graphs, what difference do you notice between the two types of averages?
2. For the 5 year running average graph, why is the time period covered shorter than the average temperature graph?
3. Estimate the 5 year running average minimum temperature in February in Davis.
4. Does the February minimum average temp graph appear to have any trends (warming or cooling)?
5. Estimate the overall average maximum temperature in July in Davis.
6. How many degrees does the running average July temperature vary by over this time period?
7. What are the advantages of using a 5 year running average for temperature?
8. What are the disadvantages of using a 5 year running average for temperature?

Click on the “Davis ground charts” tab. Here when you scroll to the right you can compare the average temperature with the 5 year, 11 year, and 21 year running average temperature.
1. What differences do you see between the different running averages?
2. What is the advantage of using a larger running average?
3. What is the disadvantage of using a larger running average?
4. If you were looking for how much year-to-year variation there is in temperature, which graph would you find most useful?
5. If you were looking for a climate change trend, which graph would you find most useful?
6. In the 21 year running average temperature, do you see a climate change trend in either the February or July data?

Conclusion

Now that you have completed this exercise, you can examine data from any location you choose to see if there has been a climate change. That is what you will be doing for Essay 1.