Climate scientists use proxy data, which is data that cannot be obtained by direct measurement but which can be inferred from other evidence. These data are obtained from a variety of natural environmental records which can indicate local conditions. For example, we know that by studying tree rings we can obtain a variety of environmental information from the area where the tree lived. Tree ring data tells us about climate conditions from long ago. This is possible because some tree species are very sensitive to moisture conditions. Scientists can see patterns of dry and wet years from the past by measuring the size of annual tree rings. Researchers can also construct temperature conditions from some types of tree ring analysis.
Scientists use a variety of mathematical techniques to make tree ring data more useful and reliable, such as comparing tree ring data with known records of precipitation for a region.
Bristlecone pine trees in the Sierra Nevada Mountains.
