1.5° — A Century and a Half, in Stripes

There is a number that scientists agreed, in Paris in 2015, we should try very hard not to cross. It is small enough to sound harmless — one and a half degrees Celsius — and it describes the whole planet, not the temperature of any place you have ever stood.

To measure it, you cannot use a thermometer. You use a baseline: the average global temperature between 1951 and 1980, a period cool enough to remember and recent enough to matter. Every year is then reported not as a temperature, but as an anomaly — how far above or below that baseline the whole Earth ran.

Below baseline, we color a year blue. Above it, red. The deeper the color, the further from the world we used to have. What follows is every year of the instrumental record, told four ways. It is the same data throughout. Only the way we look at it changes.

01 / 04 WARMING STRIPES

+0.00 °C 1880 — the first year of the record.

Movement I

Every year, a stripe.

One hundred forty-five vertical bands, oldest at the left. Each is a single year, colored by its anomaly. No axis, no numbers — just the color of the air, year over year.

Notice there is no sharp line where "cool" becomes "warm." The blue simply runs out.

Movement II

Now, the shape of it.

Give the stripes a vertical axis and they resolve into a line. The wobble of individual years is weather; the climb underneath it is climate.

For seventy years the line hovered near the baseline. Then, around 1975, it left and never came back.

Movement III

Ten years at a time.

Average each decade and the noise falls away. Every decade since the 1970s has been warmer than the one before it — a staircase with no landing.

The 2010s were the warmest decade in the instrumental record. The 2020s, so far, are hotter still.

Movement IV

Your slice of it.

The record is abstract until part of it is yours. Enter the year you were born, and every stripe since is bracketed — the warming that happened on your watch.

Born in

+1.28^°C

2024 was the warmest year in the 145-year record — and the first to run within a hair of the 1.5° line that Paris drew. Ten of the ten warmest years have all occurred since 2010.

−0.49°C

Coolest year on record: 1904. The bottom of the blue.

+1.28°C

Warmest year: 2024. A 1.77 °C swing from top to bottom of the record.

~0.2°C

Added per decade since 1975, and the rate is not slowing.

−0.5 °C · cooler than baseline1951–1980 average+1.3 °C · warmer

Notes & sources

Temperature data: GISTEMP Team, 2025 — GISS Surface Temperature Analysis (GISTEMP), version 4. NASA Goddard Institute for Space Studies. Global annual mean land–ocean temperature index, base period 1951–1980. Values shown to two decimals. Retrieved from data.giss.nasa.gov/gistemp.
Method reference: Lenssen, N., et al. (2019), Improvements in the GISTEMP uncertainty model, J. Geophys. Res. Atmos., 124.
The 1.5° threshold: the Paris Agreement (UNFCCC, 2015) commits parties to holding warming "well below 2 °C" and pursuing efforts to limit it to 1.5 °C above pre-industrial levels. Note: GISTEMP's 1951–1980 baseline sits roughly 0.2 °C above the pre-industrial reference the Agreement uses, so the two numbers are close but not identical.
Warming-stripes concept after Ed Hawkins (University of Reading, 2018). This is an original implementation.