Climate science
Global Average Temperature
The area-weighted average of surface air and sea-surface temperatures across the planet — the metric against which the Paris Agreement's 1.5 °C and 2 °C limits are defined.
Definition
Global average temperature is the mean of surface temperatures observed across the whole Earth, combining land-surface air temperature with sea-surface temperature, usually expressed as an anomaly relative to a reference period such as pre-industrial 1850–1900. WMO assessments indicate human-induced warming has reached approximately 1.4 °C above pre-industrial levels, with individual years already exceeding 1.5 °C of annual warming.
References
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Overview
What it means
The Paris Agreement's temperature goals are defined against this metric in multi-decadal terms, not single years: a year above 1. 5 °C does not breach the limit, but sustained warming does. Different datasets (HadCRUT, NOAA, NASA, ERA5) differ slightly in coverage and method, which is why the WMO blends them for official assessments.
How it is used
The metric anchors the global stocktake, IPCC carbon budgets, and annual WMO State of the Global Climate reports; media report each new record year against it.
Why it matters
It is the single number that converts the abstract concept of climate change into a trackable quantity — and the yardstick by which all mitigation effort is judged.
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