“Real time” is the actual time during which an event occurs. “Near real time” includes delays introduced by electronic communication and data processing. Here, we use the term “near real time” loosely: Data in “near real time” data sets are recent, ranging from measurements that are a few minutes to a week old.

Consistent with several other climate sources, we have defined records that extend over periods ranging from a few weeks to fifty years as “short-term” data. The definition of “short term” differs from discipline to discipline: In weather forecasting, short-term forecasts involve predicting the weather over the next few days. But in climatology, where average time scales run into centuries or more, “short-term” data can include periods of years or decades.


Records that extend over a period of fifty years or more are “long-term” data. This category includes data from the Vostok ice core (dating back over 400,000 years) and information on oak leafing in England (spanning over 200 years). In looking through this Web site, you may notice that there aren’t very many long-term data sets. The lack of reliable long-term data is one of the challenges faced by researchers investigating climate.