1.55C beyond 1.5C climate threshold registered in 2024: WMO

2024 saw the global temperature reach 1.55C for the first time, prompting it to become the warmest year on record, according to the World Meteorological Organization (WMO)

The UN’s specialized organization tasked to promote international cooperation in atmospheric science and meteorology has confirmed that the global average surface temperature in 2024 was 1.55C  above the 1850-1900 average, following its consolidated analysis of the six datasets from notable organisations with a margin of uncertainty established at ± 0.13C. The organization has also confirmed that 2024 is the warmest year on record, and the past ten years have all been in the Top Ten in an extraordinary streak of record-breaking temperatures.

“This means that we have likely just experienced the first calendar year with a global mean temperature of more than 1.5°C above the 1850-1900 average,” noted the WMO.

The organization has used the datasets based on climatological data from observing sites and ships and buoys in global marine networks, developed and maintained by the United States National Oceanic and Atmospheric Administration (NOAA), NASA’s Goddard Institute for Space Studies (NASA GISS), the UK’s Met Office in collaboration with the Climatic Research Unit at the University of East Anglia (HadCRUT), and the Berkeley Earth group. 

It has also used reanalysis datasets from the European Center for Medium Range Weather Forecasts (ECMWF) and its Copernicus Climate Change Service, and the Japan Meteorological Agency (JMA). Reanalysis combines millions of meteorological and marine observations, including from satellites, using a weather model to produce a complete three-dimensional and global dataset, the organisation noted.

However, there is a margin of uncertainty in all temperature assessments. All six datasets place 2024 as the warmest year on record and all highlight the recent rate of warming. But not all show the temperature anomaly above 1.5 °C due to differing methodologies. The timing of the release of the six temperature datasets was coordinated across the institutions in order to underline the exceptional conditions experienced during 2024, it further noted. NOAA, for instance, has registerd the temperature at 1.46C.

A separate study published in Advances in Atmospheric Sciences found that ocean warming in 2024 played a key role in the record high temperatures. The ocean is the warmest it has ever been as recorded by humans, not only at the surface but also for the upper 2000 meters, the WMO cited the study led by Prof. Lijing Cheng with the Institute of Atmospheric Physics at the Chinese Academy of Sciences, which involved a team of 54 scientists from seven countries and 31 institutes.  

About 90% of the excess heat from global warming is stored in the ocean, making ocean heat content a critical indicator of climate change. From 2023 to 2024, the global upper 2000 m ocean heat content increase is 16 zettajoules (1,021 Joules), about 140 times the world’s total electricity generation in 2023, according to the study.

“It is important to emphasize that a single year of more than 1.5C for a year does not mean that we have failed to meet Paris Agreement long-term temperature goals, which are measured over decades rather than an individual year. However, it is essential to recognize that every fraction of a degree of warming matters. Whether it is at a level below or above 1.5C of warming, every additional increment of global warming increases the impacts on our lives, economies and our planet,” said WMO Secretary-General Celeste Saulo.

The WMO noted that one or more individual years exceeding 1.5C does not mean that the world has missed the goal of “holding the increase in the global average temperature to well below 2C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5C above pre-industrial levels.” stated in the Paris Agreement.

It rather refers to an extended period, typically decades or longer, although the Agreement itself does not provide a specific definition, the organisation said. Short-term temperature spikes in long-term warming can be caused by naturally occurring phenomena like El Niño, which persisted from mid-2023 to May 2024, the organisation futher noted.

As global warming continues, there is an urgent need for careful tracking, monitoring and communication with regard to where the warming is relative to the long-term temperature goal of the Paris Agreement, to help policymakers in their deliberations. An international team of experts established by the organisation has given an initial indication that long-term global warming as assessed in 2024 is currently about 1.3C compared to the 1850-1900 baseline, it said.