- It was a period of dramatic cooling that occurred during the warming trend

- It lasted 700 years and led to enormous but short-lived changes in the climate of

  Northern Europe

- The changes were first noted in the pollen records, which indicate a change-over from

  forests to herbaceous plants and back to forest again

- In the early 1980’s, evidence for the Younger Dryas was obtained from CO₂ ice-core

  bubble measurements

- It challenges a previous debate that the climate could only change very gradually

- Demonstrates that change can be very abrupt

- Pollen obtained from lake and bog sediments provide direct information relevant to the

  reconstruction of the past flora and vegetation

- The floristic approach is reviewed, in which the modern distributions of particular

  species are compared with contemporary climatic patterns

- As a pollen assemblage at a particular time and space is a function of the regional

  flora and vegetation, and as the regional flora and vegetation are largely controlled by

  regional climate, there is thus some relationship between pollen and climate

- Pollen records from annually laminated lake sediments have a sample resolution

  similar to tree rings, tree-ring records from bristlecone pines have a time span

  approaching the length of the pollen record and high sedimentation-rate marine cores

  can, in some instances, provide a sample resolution similar to that of the pollen record.

  Such overlap is important, as it provides a means of comparing climatic estimates

  Based on one aspect of an ecosystem with estimates derived from another aspect of an

  Ecosystem

- Tree rings provide a record of local climate during the life of the tree. Many trees

  are hundreds of years old, and a few live thousands of years. Thus the rings

  provide information that is not available from scientific records

- In a tree the cambium, the cells that will become wood or bark, grow in a light layer

  during the late spring/early summer changing to a dark layer in the later summer/early

  fall

- The growth occurs at the outside of the trunk, just under the bark, so that a light and

  dark ring pair represents one year

- These annual rings can be counted to tell the age of the tree, and because there is more

  growth under good conditions, the growth patterns can be studied to determine the

  conditions a tree lived through such as forest fires, drought, insect attack, floods, or

  slopes

- The growth of a tree’s annual rings is related to the weather in the area. If it has been a

  dry summer a tree does not grow very much during that and the following year or two.

  If it was a wet summer then there is more growth. To study past weather, a scientist

  Studies trees that are very sensitive to weather changes such as the white spruce.