2024: the first year above 1.5°C

2024 was confirmed as the warmest year in the ~175-year instrumental record, at 1.55°C ± 0.13°C above the 1850–1900 pre-industrial baseline. It was the first calendar year to pass the symbolic 1.5°C mark that governments agreed in Paris to try to hold within.

One year is not the Paris threshold

A single warm year does not breach the Paris Agreement, which is defined over roughly two-decade averages. But it shows how close the long-term threshold has become. The three-year mean for 2023–2025 sits near 1.48°C, and the ten warmest years on record are all within the last decade.

2025 stepped back slightly

Preliminary figures put 2025 at about 1.44°C, marginally cooler than 2024 as a weak La Nina replaced El Nino, yet still the second or third warmest year ever measured. The underlying warming trend, driven by greenhouse gases, continues upward regardless of year-to-year swings.

The signal is unmistakable: the last eleven years are the eleven warmest on record.

What is driving it

The proximate cause of the long-term rise is the build-up of carbon dioxide and other greenhouse gases. Natural cycles such as El Nino add or subtract a few tenths of a degree on top of that trend. As long as concentrations keep rising, the baseline temperature will keep climbing with them.