Last updated by The POOG on October 26, 2020.

Most reliable and consistent direct measurement of aspects of the climate start in the nineteenth century such as the widespread use of thermometers to measure temperature. To get a longer range view of the climate, a number of proxy techniques have been developed. Examples include the analysis of ice cores, marine sediments, and tree rings.

These techniques cannot produce direct measurements but by the use of clever scientific procedures can infer climate properties such as CO2 concentration, temperature, rainfall, drought and other properties of ancient climate.

Sometimes models are developed to help supplement the laboratory analysis. It is important to understand that real science is an open and transparent process. New discoveries, new techniques, new theories are all published for peer review. Often, an important experiment will be replicated by others to confirm and validate the results. Debate may occur in the literature with the objective of reaching common agreement.

The proxy data used for climate measurement has undergone this kind of scrutiny and the time for questioning authenticity is largely past. If one wishes to reject the historical data for some reason, the climate data for the modern period – the last century or less in most cases – is meaningless for long-term trend analysis because climate operates over larger time scales.

We will include historical data in articles on specific climate components such as sea ice. Any historical data that doesn’t fit elsewhere in the climate topic will be presented in this article.