The World Meteorological Organization (WMO) used six datasets, including the one used by ECMWF, to conclude that 2024 was 1.55 degrees Celsius warmer than pre-industrial levels. Each of the six datasets found 2024 to be the warmest year ever, but not all of them recorded the warming to be in excess of 1.5 degrees Celsius.

An arbitrary mark

The 1.5 degree mark is an arbitrarily decided threshold. In terms of climate change impacts, there is nothing new that will begin to happen once this threshold is crossed. Science only says that the climate impacts are expected to become more severe and frequent as warming increases.

The 2024 breach does not mean that the 1.5 degree target is over. This target, mentioned in the 2015 Paris Agreement, refers to long-term temperature trends, usually over two to three decades, not annual or monthly averages.

The breach does not come as a surprise. The WMO as been saying for more than two years now that this threshold was almost certain to be crossed before 2027.

As a result, this new data is unlikely to trigger any fresh response measures from  countries to deal with the problem of climate change — something that has so far been severely inadequate.

Global emissions are still on the rise, and the 2030 emission cut targets are almost certain to be missed. Therefore, there is every likelihood that the breach that has happened in 2024 would become a norm within the next decade.

“One or two years that exceed 1.5 degrees Celsius above the pre-industrial level does not imply that the Paris Agreement has been breached. However, with the current rate of warming at more than 0.2 degrees Celsius per decade, the probability of breaching the 1.5 degree target of the Paris Agreement within the 2030s is highly likely,” the ECMWF said in a statement.

2023, 2024 exceptionally warm

The year 2024 has now become the warmest year ever, taking over from 2023 which was 1.45 degrees Celsius warmer than pre-industrial levels. Together, these two years were exceptionally warm, and witnessed several record-breaking temperature events. Every month since July 2023, with the exception of July 2024, has been more than 1.5 degrees Celsius warmer than the corresponding monthly average of pre-industrial times.

The years 2023 and 2024 stand out even in the rapidly warming trend witnessed in the last decade, ECMWF said. For instance, the previous warmest year, 2016, which was 1.29 degrees Celsius warmer than pre-industrial levels, was influenced by a very strong El Niño — a periodic oceanic phenomenon in the eastern Pacific Ocean that has a big impact on global weather. El Niño has a general warming effect, while its opposite phenomenon, called La Niña, has a cooling effect.

There was an El Niño prevailing during 2023 and 2024 as well, but it was mild compared to the 2015-2016 event. ECMWF said the unusual warming of 2023 and 2024 could be because of several other factors, though there was no one dominant reason. It cited “unprecedented” El Niño-like systems in multiple other ocean regions as one of the possible reasons.

An underwater volcanic eruption near Tonga in the southern Pacific Ocean in January 2022, and lower sulphur dioxide emissions from the shipping industry in 2024 could also have contributed to the warming, ECMWF said. Sulphur dioxide in the atmosphere reflects some solar radiation, thus preventing it from reaching Earth.

The unusual warming could also be because of the Sun, which was in its solar maximum phase in 2024 during its routine 11-year solar cycle. During the cycle, the magnetic poles of the Sun flip from one end to the other. ECMWF said an increase in the solar energy reaching the Earth during the solar maximum phase could have contributed to the warming.

But these are only possibilities. A more definitive analysis of the potential causes of the 2023-24 warming will come later.

Looking at 2025 and beyond

The exceptional trends seen in 2023 and 2024 are unlikely to continue this year. As of now, 2025 is not expected to emerge as the warmest year. However, it is unlikely to be substantially cooler either. In the last decade, annual temperatures have been between 1.1 and 1.4 degrees Celsius higher than pre-industrial levels, and this year is expected to fall in the same bracket.

Incidentally, the UK Met Office, in a forecast issued last month, said 2025 could very well emerge as the third warmest year ever, after 2024 and 2023.

According to a WMO report released last year, there is a possibility of annual average temperatures reaching as high as 1.9 degrees Celsius above pre-industrial levels in one of the years before 2028. The report also said that there is a 50% chance of the five-year average of annual temperatures up to 2028 exceeding the 1.5 degree Celsius threshold.