Measuring Climate

Climatologists use 30-year averages as the standard reference period. They compare current conditions to this baseline to spot trends. The main tools are temperature records, ice cores, tree rings, ocean sediment, and satellite data.

The most important measurement today is global mean surface temperature, which has now risen to roughly 1.3 degrees Celsius of human-caused warming above pre-industrial levels — and recent years have run even hotter, with 2024 becoming the first single calendar year measured at about 1.5 degrees Celsius above that baseline. Every tenth of a degree matters because the effects are nonlinear: the step from 1.5 to 2 degrees does far more damage than the first half-degree did, pushing many regions past thresholds they had stayed within.