A lot of the raw data available on the internet are held in files with different formats. Most of the data on our site have been converted from their original format to Comma Separated Value
(CSV) files which can be imported to spread-sheet programs, such as Excel, and databases, such a Access or Filemaker.
Some data are recorded at irregular intervals. One example of this is ice core data. This makes it difficult to compare data of different types or from different ice cores. The method used on this site is to produce a continuous record at the regular time step interpolating between observed values. By choosing a fine time step little detail is lost from the original record but comparison becomes much easier.
For some variables, due to instrument malfunction or other reasons, data sequences are not continuous. When there are gaps in the data it is difficult to identify trends. In such cases, providing the gap is of limited duration and provided the infilling does not it itself lead to false conclusions, we have infilled missing data. Various methods have been used and these are explained fully where appropriate.
Some files give the year value as before present (BP) with positive values for the year number; this means that time runs from right-to left when plotted normally. Other files give the calendar year; this means that time runs from left-to-right. For consistency all files are re-ordered with negative year values for times before present. This means that time on the graphs presented here always goes from left-to-right.