A century and a half on one line.
NASA GISS publishes the global land-and-ocean temperature anomaly for every year since 1880. Re-based here against the 1880-1909 mean, the line draws itself across the chart. The dashed line marks the Paris 1.5°C threshold. Five key moments mark the climb.
A century and a half on one line.
The first chart is the canonical one — the annual global temperature anomaly since 1880, drawn against the pre-industrial mean. The four notes below explain the small decisions that shaped it.
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The baseline
Most climate charts use a 1951-1980 reference. That hides almost a century of prior warming. Here the baseline is the 1880-1909 mean: every value reads as the rise above the pre-industrial world.
The dots
Five years that pulled the curve into public memory: Keeling begins measuring CO₂ on Mauna Loa, the first World Climate Conference in Geneva, the first IPCC report, the Paris Agreement, the year the line first crossed 1.5°C.
The dashed line
Paris 2015 committed signatories to hold warming well below 2°C and pursue 1.5°C. The 1.5 threshold is not a cliff edge but a political and scientific anchor. 2024 was the first calendar year on or above it.
The smoothing
The line uses Catmull-Rom smoothing between annual points. Annual values are real, the curve between them is interpolation, not data. The dots stay anchored on the measurements.
What annual means hide.
Twelve rows, one for each calendar month. Cool blue is below the 1951-1980 reference, warm orange is above. The single line above becomes a field — and the field shows that warming is not even: northern winter months and the Arctic are heating faster than tropical summers.
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Each cell is one calendar month. Hover anywhere to read the value. The colour ramp is symmetric around zero so the field tilts visibly from cool to warm as you scan left to right.
CO₂ climbs with us.
Atmospheric carbon dioxide, measured continuously on Mauna Loa since 1958. The line slope is steeper than the temperature line because CO₂ has no decadal noise — the temperature curve wobbles around the trend, the CO₂ curve barely does. Two dashed lines mark thresholds: 350 ppm, the level Bill McKibben's 350.org named in 2007 as the safe upper bound, and 400 ppm, crossed for good in 2013.
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The annual mean smooths out the seasonal saw-tooth — northern hemisphere plants pulling CO₂ down each summer and releasing it each winter. The trend underneath is monotonic. Latest reading is from NOAA's annual report.
One line, one grid, one parallel curve. The same century told three different ways.
Data: NASA GISS GISTEMP v4 (annual + monthly), NOAA Mauna Loa (annual CO₂) · Baseline annual chart: 1880-1909 mean · Curves: hand-rolled SVG with Catmull-Rom smoothing · Reveal: stroke-dasharray and per-column wave · All hover, no clicks