Pre-industrial baseline
A reference period used to compare present temperatures with conditions before large-scale industrial warming.
Example
Assessments often use 1850 to 1900 because observations provide a workable historical reference.
The catch
The baseline must be named when comparing temperature anomalies.
Related terms
Albedo, Atmospheric lifetime, Carbon budget, Carbon dioxide, Climate change, Climate feedback
In more depth
Pre-industrial baseline, explained.
The pre-industrial baseline is a practical approximation, since some human-caused warming had already begun before the reference period that IPCC assessments use. The Paris Agreement itself refers to pre-industrial levels without defining a period, and scientific practice fills the gap.
Weather services often report anomalies against a recent multi-decade average, which produces smaller numbers for the same temperature. Moving between baselines needs a stated offset, and mixing them can make a year look cooler or hotter than it was against the Paris goals. Global warming levels refer to long-term averages, so a single hot month above a threshold says little about the level the world has reached.