Which year was the hottest on record globally and by how much did it exceed the average?
Executive summary
Global climate monitoring agencies now point to 2024 as the warmest year on instrumental record, and it exceeded long-standing baselines by more than a degree Celsius—though the exact number depends on the dataset and the reference period used (20th‑century vs. pre‑industrial) [1] [2] [3].
1. 2024: the year that topped the charts
Multiple international authorities—NOAA, the World Meteorological Organization (WMO) and the Copernicus Climate Change Service—have concluded that 2024 was the warmest calendar year on record based on consolidated analyses of global surface temperature datasets [1] [2] [3]; earlier proclamations that 2023 was the hottest (from NOAA and NASA at the time) were overtaken by later analyses and longer records that included 2024, which showed an even higher global mean [4] [5] [6].
2. How much hotter: the numbers and the baselines
Reported anomalies differ because agencies use different baselines and ensemble datasets: NOAA reported 2024 at about 1.29°C above the 20th‑century (1901–2000) average and roughly 1.46°C above the pre‑industrial (1850–1900) baseline in their 2024 assessment [1], while the WMO’s consolidated multi‑dataset analysis placed 2024 at about 1.55°C above the 1850–1900 average (with an uncertainty of ±0.13°C) [2]; Copernicus’ ERA5‑based conclusion similarly identifies 2024 as the warmest year and was the first calendar year to exceed 1.5°C above pre‑industrial levels in their record [3] [7].
3. Why the same fact yields different decimals: datasets, baselines and uncertainty
Surface temperature reconstructions rely on multiple inputs and methodological choices—land and sea coverage, gap‑filling, bias corrections and the exact pre‑industrial or 20th‑century baseline—so NOAA, Copernicus, WMO and NASA can each report slightly different anomalies for the same year while agreeing on the overall conclusion that recent years are the warmest on record [1] [7] [2] [6]; agencies also publish margins of uncertainty (for example WMO ±0.13°C) to communicate the statistical spread across datasets [2].
4. How this compares to earlier “warmest year” claims
The narrative shifted: agencies initially identified 2023 as the warmest year in several datasets—NOAA and NASA released 2023‑focused analyses showing 2023 beating previous records by clear margins [4] [5] [6]—but comprehensive, cross‑dataset assessments that included full 2024 observations and reanalyses found 2024 to be hotter, demonstrating how single‑year rankings can change as more complete datasets are consolidated [1] [2] [3].
5. Bigger picture: trend, drivers and implications
Beyond the single‑year headline, all agencies underline a clear trend: the past decade contains the warmest years in the instrumental record and multiyear averages now approach and in some cases exceed the 1.5°C threshold above pre‑industrial levels, driven by accumulating greenhouse gases with short‑term modulation from El Niño/La Niña cycles and other natural variability; that means record years are symptoms of a long‑term warming trend rather than isolated anomalies [2] [3] [4].
6. What remains uncertain or contested
While the qualitative conclusion—2024 as the warmest year—has broad agreement, the precise magnitude (e.g., 1.29°C vs. 1.46°C vs. 1.55°C above various baselines) varies by dataset and the pre‑industrial/20th‑century reference chosen, and agencies note margins of uncertainty and methodological differences explicitly in their reports [1] [2] [7]; where a single decimal matters, the choice of baseline and dataset must be stated alongside the headline.