Flowering times: Are they a-changin'? 

This exercise was developed by Thomas DiMauro, a student in biology and education at the University of Connecticut. It analyzes change in the mean annual temperature in Connecticut in the past 100 years and investigates whether the flowering time of plants may have changed in response.

Many of us have heard about climate change and global warming, but how can we tell that our climate really is changing? And how dramatic is that change?  Scientists have begun to use herbaria, which are collections of thousands or millions of preserved plants collected over hundreds of years, to look for changes in plants that might correspond to changes in our climate. Students now can play the role of botanist and see if there is evidence connecting when plants start to flower in the spring with changes in recorded temperature over the past century. (Additional information on the exercise that teachers may find useful is available here.)

PART I: Is there evidence of climate change?

First, you have to see if there is evidence of a changing climate.  There are many signs that climatologists look for.  In this first exercise, you will investigate the average yearly temperature in Connecticut during the past 100 years.  To do this, follow these directions.

       A.  Find the average annual temperatures in Connecticut for the past century.   Go to the website of the National Oceanic & Atmospheric Administration, which contains a wealth of information about the nation's climate, weather  predictions, climatic history, and much more.

      B.  Choose the “US Climate Division” dataset, then go to the next page of selection options.

      C.  Select “Connecticut” as the state. In “Division,” select the final option, “State area averaged.”

      D.  Set the year range to span from 1900 to 2009, and where the option is given to choose either “Monthly” or “Seasonal Average” temperatures, choose Seasonal Average, setting the “first month” as January and the “second month” as December.  Be sure to do this! If you just choose to list the monthly temperatures, it will show you the average temperature of each of the twelve months of that year.  By choosing “Seasonal Average” and having it range from January to December, it will average the data for all those months and give you, essentially, the yearly average temperature.

      E.   Leave the Output Format as “Raw Data values” and click on “Create Timeseries.”

      F.   Now download the Excel file AverageTemperatureGraphs.

      G.  Copy and paste the temperature data from the NOAA website into Column A, third row (Cell A3) of the Excel file. The Excel file is formatted to display the NOAA data in a useful way. After pasting the information from the NOAA website into the spreadsheet, the first 6 columns should fill with data.

      H.  Now that you have data, create a chart to display it.  To do so, highlight columns E and F.  Then click “Insert” at the top of the screen, and choose “Chart.”  A graph should appear in the document with a lot of options to choose from.  Choose to make an “XY (Scatter)”, and click “Next” to see a preview of your graph.

      I.    Click “Next” once more and enter the name of your species into the “Chart Title.” For the “Value (X) Axis,” enter the label for the X-axis (which is also the title of Column L), and for “Value (Y) Axis,” enter the label for the Y-axis (title of Column M). Finally, click “Finish.”

      J.    The graph should now contain a lot of points, labeled axes, and a title. Adding a  trendline would show any overall trend in the data over the past century.  To add a trend line, right-click on one of the points on the graph and choose “Add trendline.”  Click on the tab titled “Options” and choose “Display equation” and “Display R-squared value on chart.” Then click “OK.”

      K.  There should now be a straight line in the scatterplot, plus an equation and an R2 value.  The R2 value tells us how precisely the best-fit line fits the available data.  It ranges from 0 to 1, where 0 represents no trend, and 1 means a very reliable method of prediction.  Write the equation and value of R2 here (to download these instructions as a text file in which you can write answers to these questions, click here):

                  y = ________________________________________    R2 = ____________

      L.   Return to the NOAA website (Step A) and repeat steps D through K, but choose a specific month or “season” that you would like to investigate.  Instead of finding average temperatures for the entire year, you will be finding the average temperature for a month or season of your choice.  For either of these options, you will want to stick with calculating Seasonal Averages as opposed to Monthly.

  •  If you want to see the trend of average temperatures in a specific month (March, for example), simply set both the first and second months as the month you are researching (so, both would be March in this case).
  • If you want to see the trend of seasonal temperatures, just set the first and second months as the months that begin and end the season.  For example, if you wanted to investigate the average seasonal temperature for the summer, set the first month as June and the second month September.  You're welcome to choose any length or time of season.
  • When you decide what season or month you will investigate, write it down.  If you want to do a season, write the first month and the last month in the season.


      M.  Create a graph for your data set in the same Excel file, making sure to paste the information  into column A starting with cell A118.  Write the equation for the best-fit line and its R2 value:
                  y = ________________________________________    R2 = ____________

            Include all the necessary information, as in the previous graph, and make sure you specify which month or season you are researching.  Print out the two graphs.

Analyze your data

Compare the graph showing the average annual temperature trends to the graph showing the seasonal trend.  Think about what you see and what they mean to us in real life.

      1.   What does the average yearly graph show?  Is the average temperature in Connecticut changing?  If so, is it getting warmer or cooler?  How can you tell?

      2.   What about the graph showing your choice of season or month?  Is Connecticut experiencing any change in the temperature during that period? How can you tell?

      3.   In the equations for your best-fit lines on the graphs, there is a coefficient for X.  What is it for each of the two equations and what does it mean?

     4. Compare the trends you see in your graphs.  Are they similar or different?  Does one have a stronger trend than the other?

PART II: Are plants flowering at different times?

First, you need to determine if flowering time for your species has changed over time, which could be evidence that climate change is affecting it. Follow these steps to navigate the UConn Virtual Herbarium and obtain your data:

A.    First, write down the scientific name of the species you will research (the species will be assigned to you or you may be asked by your teacher to select the species from a list):


B.     Investigate the times when your flowering plants were collected.  Using a computer, go to this website: http://bgbaseserver.eeb.uconn.edu/Teacher_website/SpeciesFiles/

C.     Look for your species name and click on the file, choosing to “Open” the file with Microsoft Excel.

D.    Once the file is open, highlight the last two columns (L and M), which are labeled “YEAR” and “JULIAN DAY.”  The Julian Day is what day of the year it is if you started to count from Jan. 1 and continued through the year. The Julian Day for Dec. 31 thus would be 365 (except for leap years).

E.     With columns L and M highlighted, create a graph for this data the same way you did in Part I. Label the X- and Y-axes, use your species' scientific name as the graph's title. Include the trend line, equation and R2 value.  Write the last two items here:
                        y = ________________________________________          R2 = ____________   

F.      You can now print out the graph and the data you downloaded from the Virtual Herbarium.  Make sure your name is on both.

 Analyze your data

Now that you've looked at the data for your specimen, the most important thing is that you know what it means.  Answer the following questions to help you better understand exactly what you're looking at.

       1.   What is the value of the coefficient for x in your equation?  What does it mean?

      2.   Is your plant species flowering around the same day now as it was 100 years ago?  If not, is your species now flowering earlier or later?

      3.   Describe the relationship between temperature and flowering time in your species (Something like: “In the past 100 years, as average temperatures have ______, flowering time in this species has _____.”)

       Is this the relationship we would expect?

Conclusions and Scientific Predictions

1.      Now compare your graphs with those your classmates produced for different seasons and for different species.

2.      Is the temperature changing in a consistent way throughout the year or are there some periods during which temperature has changed more than others?

3.      What about flowering times?  Did every species respond in the same way to changes in temperature, or were there species whose response was inconsistent? Why might this happen? How might this be important for the plant?

    4.    Is there a reason to be concerned if flowers are starting to bloom at different times than they did 100 years ago?  Why should we care?  Think about animals that rely on plants and their flowers.

    5. Rising temperatures are only one component of “global climate change.” Other changes include alteration of rainfall patterns – more rain in some places, less in some and changes in when the rain comes in still others – rising levels of carbon dioxide in the atmosphere, and atmospheric deposition of nitrogen, which is an element that plants need. How might we look for evidence of changes in these conditions in Connecticut?

    6. How might changes in these other conditions affect plants? How would we look for evidence that changes in other conditions are affecting plants?

is important to remember that many conditions – not just temperature – affect flowering time in plants. We have not proved that warming has caused change in flowering time. We would need to do additional analyses to test whether flowering time actually is affected by other conditions. Still, we have evidence that flowering time may be related to warming conditions, and the more evidence we accumulate, the more confident we can feel that global climate change is affecting the plants around us.

Food for Thought...


                        --Barack Obama

The good news is, we have everything we need now to respond to the challenge of global warming. We have all the technologies we need, more are being developed. ... But we should not wait, we cannot wait, we must not wait.

                        --Al Gore