Global Temperature Anomaly: How Much the Earth Has Warmed

The single clearest measure of climate change is the global temperature anomaly — how far each year's average temperature departs from a long-term baseline. The record stretches back more than 175 years, and it tells an unambiguous story: after a century of small wobbles around the average, temperatures have climbed sharply since the 1970s, and the warmest years on record are all recent. This guide explains what the anomaly measures, how much Earth has warmed, and why the 1.5°C threshold matters.

What is a temperature anomaly?

A temperature anomaly is the difference between a given year's average temperature and a long-term baseline — here, the 20th-century average. Scientists track anomalies rather than absolute temperatures because they combine cleanly across thousands of land and ocean measurement points around the world. A positive anomaly means warmer than the baseline; the dashed line on the chart marks zero, and the steady climb above it is global warming made visible.

How much has Earth warmed?

Global temperatures are now more than 1°C above the 20th-century average — and about 1.3°C above the pre-industrial levels of the 1850s, when the record begins. That may sound small, but a single degree of global average warming represents an enormous amount of accumulated heat, enough to shift weather patterns, raise sea levels, intensify storms and droughts, and melt ice sheets. The warming is also uneven: land and the Arctic have warmed far more than the global average.

The recent acceleration

The chart's shape is the famous "hockey stick": relatively flat for the first century, then bending sharply upward from the 1970s onward. The pace of warming has accelerated as greenhouse-gas concentrations climbed, and the hottest years in the entire record are clustered in the most recent years — each new record often surpassing the last. This acceleration closely tracks the rise in atmospheric carbon dioxide from burning fossil fuels.

Why 1.5°C matters

You'll often hear about limiting warming to 1.5°C above pre-industrial levels — the central goal of the Paris Climate Agreement. It's not a magic cliff-edge, but scientists identify it as a threshold beyond which the risks of severe, irreversible impacts — collapsing ice sheets, dying coral reefs, deadly heat waves — rise steeply. With warming already near 1.3°C and still climbing, that target is perilously close, which is why the slope of this line is one of the most consequential trends on Earth.