A piece of evidence – such as a tree-ring or an ice core - that is used to estimate the temperatures that prevailed prior to the invention of thermometers.
Quote: "A note for those new to temperature history. Proper temperature measurement on a worldwide basis only goes back into the second half of the 19th century. And the longest temperature series (from Central England) only goes back to the mid 17th century. So all attempts to measure the past history of our climate rely on proxies. Temperature proxies include ice core data and tree rings. Proxies aren’t like perfect thermometers and the further you go back the more difficult the analysis becomes." (Science of Doom)
Why they are used
In the following, NCAR scientists Caspar Ammann and Kevin Trenberth (and others) explain why they use them in their computer models.
1. Click here to read a paper about the use of French grape harvests as proxies.
2. Click here to read about a 2011 study that used proxies to determine Northern Hemisphere temperatures for the last 2000 years.