Does the Solar Cycle Affect Earth?

The sunspot cycle seems to be fairly predictable when the average number of sunspots per year since 1900 is graphed.
The records from the 1600's show a different pattern.  For a period of about 70 years there were very few sunspots seen, and years went by between sightings.

This break in the cycle is called the Maunder Minimum.   Historical records from this period show that winters were unusually cold.  Some researchers have even labeled it a mini-ice age!

The extreme conditions associated with the lack of sunspots during the Maunder Minimum made scientists wonder if  storms on the surface of the Sun effect weather conditions on Earth.  They began to look for evidence of connections between rainfall and temperature patterns and the sunspot cycle.  Maunder Minimum and Maunder Maximum


Investigation One: Investigate weather patterns

One of the ways scientists can investigate weather conditions in the past is to study tree rings.  Each ring stands for a year of growth.  The rings vary in width according to growing conditions.  Rings that are wider than the average indicate greater than normal growth, which can be due to increased rainfall or other factors.  Rings that are narrower are a sign that something interfered with the normal growth pattern.

     * Actual or photographic tree cross-section

1. Analyze the width of the tree rings to identify the tree's growth patterns. 

    *What can you tell about the growing conditions 
        for this tree during its lifetime? 

    *What are the possible ways that weather affects the 
        growth of tree rings? 


Learn more about tree ring dating and dendrochronology.

Investigation Two:  Use tree rings to date an event

Here is a diagram of a tree cross-section.  The tree grew in Alaska twenty-nine miles from the Katmai Volcano.  The ring next to the bark layer was the last to grow.  Some of the lines between the rings have been darkened to make it easier for you to count the rings.

The tree was cut down in 1962.  Mt. Katmai erupted during this tree's lifetime.  The forest was blanketed in ash for several years.  The tree survived but many other plants in the understory of the forest did not.  With little competition for water and nutrients for a time, the tree grew better than before the eruption.

    * Tree ring picture PDF (US Geological Service)

1. Access or print the PDF to see the entire diagram.
2. Count the tree rings to find the age of the tree.
3. Compare the widths of the rings to identify the growth patterns.

    *What year did the volcano erupt?  How do you know?

Learn more about volcanoes and tree rings.

Investigation Three:  Connect tree rings and sunspot cycles

A.E. Douglas, who started the tree ring laboratory at the University of Arizona, discovered that tree rings from the years of the Maunder Minimum were remarkably even.  He began to search for proof that the sunspot cycle causes changes in the weather on the Earth.  To date, not enough evidence from tree rings has been collected to prove or disprove a connection.

You can contribute to the research by conducting your own investigation of tree rings and the sunspot cycle.

Here is an actual photograph of two cross-section samples of the same tree.  Scroll to the far right of the screen to see the whole samples and to distinguish the rings from the diagonal saw marks which go across them.  There are 10 rings between each decade marker.  Sample 023 allows you to see the rings between 1900 and 1910 which are not visible on Sample 022.

    * completed Sunspots Over Time Graph (See Investigate the Solar Cycle)

1. Count the rings from the 1980 decade marker to the bark layer to find the year the tree was cut down.
2. Start at 1980 and find the year for the widest ring in each full decade going back through the lifetime of the tree to 1900.
3. Mark the year of the widest ring in each decade on the completed Sunspots Over Time Graph.

    *Are there any relationships between the number of sunspots and the best growing conditions?
    *What are the problems with getting weather data from tree rings?

Look at more tree samples.


Extensions: Look for other connections

Scientists continue to look for other connections between sunspots and conditions on Earth.  Over the years, people have explored ideas as diverse as relating the sunspot cycle to the stock market and to the rabbit population in Australia!   The data of many different phenomena show cycles with peaks and valleys, but do these cycles match the solar cycle?  Here are some data sources to start you looking for connections.

    * Did sunspots cause the sinking of the Titanic?
    * Are land and surface temperatures related to sunspots?
    * To look for weather and climate information:
    * Are there any connections between events in history and the sunspot cycle?

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