Extrapolation

Extending a trend beyond the data is extrapolation and is less reliable: the relationship may change outside the measured range.

Extending a trend beyond the measured range is extrapolation, which is less secure because the pattern might change. This matters when interpreting earth-system data: a graph may show that atmospheric carbon dioxide and another quantity change together, but that relationship alone does not prove what caused either change. State what the data shows, then distinguish it from an explanation that needs further evidence.

Extrapolation means estimating beyond the measured range.