The State of the Global Climate 2024

Simon Maxwell

This is mainly to recommend the latest annual report from the World Meteorological Organisation on the State of the Global Climate, published on 19 March. It is authoritative, readable – and short. A brief summary follows, with comments at the end.

WMO tracks seven indicators to monitor the climate. These are:

Atmospheric carbon dioxide
Global mean near-surface temperature
Ocean heat content
Global mean sea level
Ocean pH
Glacier mass balance
Sea-ice extent

The WMO also looks at temperature and precipitation, and at high-impact events. It publishes a supplement on the latter, here.

It will not be a surprise that all the indicators are heading in the wrong direction. Celeste Saulo, the Director-General of the WMO summarises the report as follows:

‘The annually averaged global mean near-surface temperature in 2024 was 1.55 °C ± 0.13 °C above the 1850–1900 average. This is the warmest year in the 175-year observational record, beating the previous record set only the year before. While a single year above 1.5 °C of warming does not indicate that the long-term temperature goals of the Paris Agreement are out of reach, it is a wake-up call that we are increasing the risks to our lives, economies and the planet. Over the course of 2024, our oceans continued to warm, sea levels continued to rise, and acidification increased. The frozen parts of Earth’s surface, known as the cryosphere, are melting at an alarming rate: glaciers continue to retreat, and Antarctic sea ice reached the second-lowest extent ever recorded. Meanwhile, extreme weather continues to have devastating consequences around the world.’

The seven key graphics are pasted in below for ease of reference. The Report provides explanation and context.

My comments are as follows:

1. The Report makes the point that the record temperatures in 2023 and 2024 were partly driven by higher than average sea-surface temperatures in the eastern tropical Pacific, a phenomenon known as El Nino, which peaked between November 2023 and January 2024. However, there is cause for concern that the temperature anomalies may have been higher than expected and to have continued for longer. The WMO Report has a box on this (Pgs 23-4), and there is a wider literature (see e.g. here).

2. It looks from the headline figure as though the Paris Agreement goal of limiting warming to 1.5 degrees has been breached. However, the WMO report reminds us that the target is defined as a rise in mean temperatures over several decades. It will take some time, including in years without El Nino, before a rise of 1.5 degrees can be established and confirmed. This is a problem, though. By the time a moving average of some kind has breached 1.5 degrees, the current temperature rise is likely to be above that – on best estimates about 0.2 degrees higher. So, when the ‘official’ threshold of 1.5 is reached, the actual temperature rise may be about 1.7 degrees. That’s not helpful. Again, there is a literature – see this summary from Carbon Brief.

3. The rise in CO2 concentration looks alarming, and it is. But if you look at the WMO graph in the set I have pasted in at the end, it is not really rising exponentially. In fact the graph is pretty well a straight line, which suggests that the rate of growth might be slowing. I tried re-casting the data as a semi-log graph, and also calculated the annual growth rate separately. The results (Figure 1) are not entirely reassuring: the long term trend looks like an acceleration (though with a lot of variation).

4. The report makes the point that methane emissions are also rising. This is important because of the short term warming effect of methane – more than 80 times that of CO2 on a 20-year time-scale. Some of the increase could be anthropogenic, caused by the impact of human-induced warming on methane emissions from wetlands. UN Environment has an annual report on methane.

5. And that is important because modelling of least cost pathways to net zero presented in the IPCC report of 2021 assumed that both CO2 and methane emissions began falling in 2020. In fact, neither did. In the Emissions Gap Report, we called these ‘excess emissions’. I prefer the term ‘zombie emissions’ – emissions which should not be alive, but unfortunately roam the atmosphere unchecked. To my mind, zombie emissions cast serious doubt on the value of using current modelled pathways without adjustment.

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Figures from the State of the Global Climate 2024

1. Atmospheric carbon dioxide