The 1.5 °C limit set by the Paris Climate Agreement was breached in 2024. What now?

Over recent months, the World Meteorological Organization of the United Nations has been warning that 2024 would in all likelihood be the hottest year ever recorded, overtaking the record previously set in 2023. Recently Copernicus, the Earth observation component of the European Union’s scientific collaboration programme, has confirmed this prediction.

The news has been picked up by almost all international media, giving rise to a great deal of concern. This is due especially to the fact that 2024 is the first year in which the 1.5 °C limit set by the Paris Climate Agreement — the most important international treaty on combating global warming — was exceeded over such a long period. It has been accepted for some time that this threshold would be crossed, partly because the past decade has been the hottest on record, but the 1.5 °C goal remains important nonetheless, not least as a formality.

In addition to this comes the update shared by Copernicus, that the month of January 2025 has been the warmest on record globally. Its average surface air temperature of 13.23 degrees centigrade is 1.75 degrees higher than the estimated average for 1850-1900, the period used as reference for pre-industrial levels, and 0.79 degrees higher than the 1991-2020 January average.

The temporary crossing of the 1.5 °C threshold does not, however, mean that the Paris Agreement no longer serves any purpose. The limit applies to the current decade, and represents the goal of ensuring that the average increase in temperature has not passed that threshold by 2030. It is still true that, given current trends, this target is highly likely to be missed and 1.5 °C exceeded, entailing an increased likelihood of extreme weather events. Heatwaves, hurricanes, floods and drought will become even more frequent and intense, with all the associated knock-on effects, such as the predictable rise in movements of people in connection with climate migration.

The 1.5 °C threshold was set as the most optimistic target under the Paris Climate Agreement. In this sense, it is a "political" limit more than a scientific one, and carries immense symbolic weight. The importance of remaining within 1.5 °C became even clearer in 2018, when a UN report compared that limit with the 2 °C target, illustrating the difference that just half a degree more would make: a further increase in the risk of disastrous weather events happening more and more frequently. The World Meteorological Organization (WMO) has, however, emphasised that the Paris Agreement’s best-case target can only be considered failed if the average global temperature is 1.5 °C higher than the pre-industrial era over at least twenty years.

The increase in the average global temperature in 2024 can also be traced back to the effects of the El Niño climate phenomenon. This cluster of weather events, which arises at intervals in the Pacific Ocean, has a significant impact on climate across much of the planet, causing a rise in temperatures and a drop in precipitation, among other effects. El Niño weighed particularly heavily on 2023, but some of its residual effects influenced part of 2024. In addition to this are the continuing effects of emissions linked to the consumption of fossil fuels.

Copernicus has calculated that the average global temperature increase came to 1.6 °C in 2024, with other international agencies involved in analysing climate trends reporting similar values. According to the European Union’s programme, 2024 was 0.12 °C hotter than 2023 and 0.72 °C hotter than the average for the period 1991-2020. All months from January to June 2024 were hotter than their counterparts in previous years — at least, since such records began to be kept. Specifically, the latter decades of the nineteenth century are used as the benchmark for average global temperature. At this time, industrialisation levels were very low, with the result that there was little mass emission into the atmosphere of large quantities of carbon dioxide — the main greenhouse gas — caused by human activities. The leading cause of the rise in average global temperatures is, in fact, the accumulation of greenhouse gases, due in particular to the use of fossil fuels.