Uncertainty

Uncertainty describes limits on how precisely a value or outcome is known. It does not mean that scientists know nothing or that all explanations are equally likely.

Uncertainty increases if monitoring sites are unevenly distributed or if oceans and remote regions are poorly represented. A record from one city or country cannot automatically represent the whole planet. Coverage was much less complete during the nineteenth century, improved when Antarctic measurements began after 1957, and became better again with satellite observations from about 1980.

There are still uncertainties. An individual temperature reading can be affected by an instrument's precision and local conditions, such as altitude or a nearby city. Older climate evidence is less direct than modern measurements.

All measurements have uncertainty. Older thermometer records have less complete geographical coverage than modern records, instruments and observation methods have changed, and individual readings are affected by local conditions. Researchers correct and compare records, but a calculated global average still has a range of uncertainty.