CG6. Collecting climate data from plants. Vicky Wong. Page 1 of 4
Collecting climate data from plants
One of the ways of finding out about past climates is to look at the remains of plants. Often
these are preserved or fossilised and they can be thousands or even millions of years old.
.
By studying different types of plants, data about annual temperature ranges and water
availability when the plant was alive can be collected. Dating the rocks where these plants are
found is done in a number of ways, but includes looking at fossilised animals and pollen found in
the same area and the position in the rock layers where the plants are found.
Many different methods are used to gather climate data. Three of them are explored below.
Fossil flora
In this method, fossilised plants are compared to the nearest living plants which are known
today. By considering the conditions under which the plants alive now live, extrapolations are
made to the fossilised ones. This can be used to estimate the temperature.
1. What do you think is the main problem with this method?
Leaves as thermometers
The shape of the leaves, the nature of the leaf margin (the outside of the leaf) and the features
of the leaf cuticle can all be used to provide estimates of mean annual temperature, temperature
range and water availability. This method has been developed over a number of years and
there is a clear relationship between the temperature when the leaves were growing and the
percentage of smooth leaves found in a group of leaves. The group of leaves is called an
‘assemblage.’
The graph to show the relationship between the mean annual temperature and the percentage
of leaves which have smooth margins is shown below:
CG6. Collecting climate data from plants. Vicky Wong. Page 2 of 4
From Climate Change , Dorothy Warren, Royal Society of Chemistry 2001 - originally modified with permission from
the Open University – P. Skelton, B. Spicer and A. Rees, Evolving Life and the Earth, Milton Keynes: The Open
University, 1997.
CG6. Collecting climate data from plants. Vicky Wong. Page 3 of 4
2. Using the graph, work out the mean annual temperature if the following leaves were
found together in an assemblage.
3. What do you think are the main problems with this method?
Tree Growth Rings
In areas of the world where there are large variations between summer and winter climate,
many trees form clear, annual growth rings around their circumference. The thickness of these
rings depends on many things including temperature, water availability, light levels, which
insects were around and how long the growing season was. The rings can also be affected by
variation in the concentration of gases in the atmosphere. By studying these tree rings,
scientists have access to a year-by-year record of the climate stretching back hundreds, and
sometimes thousands, of years. Fossilised trees can also be used, providing data which goes
back even further.
CG6. Collecting climate data from plants. Vicky Wong. Page 4 of 4
Photograph A
Photograph B
From Climate Change , Dorothy Warren, Royal Society of Chemistry 2001 - originally reproduced with permission of
Jane Francis, University of Leeds.
The round holes in photograph B were formed by boring worms when the tree was driftwood.
The holes were then filled with sea floor sediment. This wood is now petrified (turned to stone).
The wood in photograph A is also from a fossil.
4. Which tree lived in a warm, wet climate?
5. Which tree lived through periods of drought?