Tree ring dating and climate change
A tree ring consists of two layers: At locations where tree growth is limited by water availability, trees will produce wider rings during wet and cool years than during hot and dry years and the rings are wider.
Drought or a severe winter can cause narrower rings too.
Tree growth depends upon local environmental conditions.
In some areas the limiting factor for growth is water availability, in other areas (especially at high latitudes) it is the length of the growing season.
The study of the growth of tree rings is known as dendrochronology.
The study of the relationship between climate and tree growth in an effort to reconstruct past climates is known as dendroclimatology.
The first, "Build a Tree", allows you to specify the conditions (temperature and precipitation) in the vicinity of a tree on a yearly basis, and to see how those conditions influence tree ring growth.
The second, "Splice Tree Ring Records Together to form a Longer Chronology", invites you to align the records from three samples of wood to generate a longer record of climate history.
Computer analysis and other methods have allowed scientists to better understand certain large-scale climatic changes that have occurred in past centuries.
Matching these patterns can show the year a tree was cut, thus revealing the age of a dwelling.
Tree ring data is only collected outside of the tropics.
Tree ring records can be combined to create climate records that span a timeframe longer than the life of a single tree.
For example, the data from a living, 200-year old tree could be combined with a data from wood from a tree that was felled 150 years ago (after living a couple of centuries) to produce a composite dataset spanning several hundred years.This map shows sites from which tree ring samples have been gathered.