Spring Brings High Sea Levels and Warm Nights

The Australian Actuaries Climate Index (AACI) for spring 2024 shows extreme high sea levels and unusually warm minimum temperatures.

The AACI shows that sea levels were unusually high in the spring of 2024. This was especially notable in the Monsoonal North region, which covers most of the northern part of Australia, where the highest ever extreme sea level index value was recorded.   

 

Elevated sea surface temperatures are likely to have contributed to this. When the ocean is warmer, it expands, leading to higher sea levels. Copernicus, the European Union’s Earth observation program, notes that in 2024 the sea surface temperature exceeded the 1991-2020 average for 91% of the globe.[1] They were particularly elevated for the tropic’s regions, including northern Australia.

In addition, the extreme low temperature index showed unusually warm low temperatures, with every part of the country observing extreme minimum temperatures that were warmer than the reference period average.

 

The Rangelands South region, which covers large parts of the southern half of the country, observed the highest extreme low temperature index value to date. This aligns with the Bureau of Meteorology’s observation that the mean minimum temperature was the highest on record in the north of South Australia.[2]

 

As well as climate change directly influencing these warmer temperatures, the elevated sea surface temperatures may have also contributed. High sea surface temperatures lead to greater evaporation and a warmer atmosphere has the capacity to hold more water. This increased atmospheric moisture traps heat and can prevent the temperature from dropping during the night.

Copernicus has shown that the total amount of water in the atmosphere reached a record level in 2024, as shown in the graph below.[3]

Looking forward

The oceans around Australia have continued to be unusually warm in the summer of 2024/25, with the Bureau of Meteorology noting that sea surface temperatures were the warmest on record during December 2024.[4]

In addition, summer is shaping up to be warmer and wetter than average, with thunderstorms observed on parts of the east coast. From February to April, the Bureau of Meteorology has predicted above-average rainfall for much of northern and eastern Australia (with an increased chance of unusually high rainfall). This is especially likely in parts of northern and central Queensland. Warmer than average days and nights are also deemed likely across Australia.[5]

The National Oceanic and Atmospheric Administration (NOAA) in the U.S. declared a La Niña event emerging in December.[6] This could increase the prospects of heavy rainfall, especially on Australia’s East Coast. However, the Bureau of Meteorology has a higher threshold for declaring a La Niña event and considers the El Niño Southern Oscillation (ENSO) system to remain neutral. NOAA has stated that the late emerging La Niña is likely to be weak and will therefore have limited impact.

The Bureau of Meteorology has forecast the ENSO weather system to remain neutral until the winter of 2025, indicating that this particular weather system is unlikely to drive significant deviations from typical weather patterns. 

Background

The Index measures the frequency of extreme weather conditions and sea levels across Australia and how these vary over time. Components cover extreme high and low temperatures, extreme rainfall, consecutive dry days, extreme wind and sea level. The Index was launched in November 2018 by the Actuaries Institute and is updated four times a year by Finity Consulting for the Actuaries Institute.

Unlike many other measures, the AACI focuses on changes in the extremes. This is a more relevant metric for the insurance industry (and others) than averages, as it correlates more closely with damage. This is done by measuring how often we observe the current quarter’s observations exceeding the 99th percentile of the corresponding observations in the reference period of 1981-2010. More details and full results can be found on the microsite.

The purpose of the AACI is to provide a publicly available and objective measure of extreme weather conditions and is one way in which the actuarial profession can contribute to the assessment of climate risk.

Alongside the North American Actuaries Climate Index,[7] it is one of two climate indices produced globally on behalf of actuarial associations and has been referenced extensively in the media and other reports.[8]

References

[1] Copernicus Climate Change Service. (2024). Global climate highlights 2024. Retrieved from https://climate.copernicus.eu/global-climate-highlights-2024

[2] Bureau of Meteorology. (2024, November). Seasonal climate summary: South Australia. Retrieved from http://www.bom.gov.au/climate/current/season/sa/archive/202411.summary.shtml

[3] Copernicus Climate Change Service. (2025, January 10). Global climate highlights 2024. Copernicus. https://climate.copernicus.eu/global-climate-highlights-2024

[4] Bureau of Meteorology. (n.d.). El Niño-Southern Oscillation (ENSO): Overview. Australian Government. Retrieved January 31, 2025, from http://www.bom.gov.au/climate/enso/?ninoIndex=nino3.4&index=nino34&period=weekly#tabs=Overview&overview-section=Summary

[5] Bureau of Meteorology. (n.d.). Climate outlooks. Retrieved from http://www.bom.gov.au/climate/ahead/outlooks/

[6] National Oceanic and Atmospheric Administration (NOAA). (2025, January). ENSO update: La Niña is here. Retrieved from https://www.climate.gov/news-features/blogs/enso/january-2025-update-la-nina-here

[7] Actuaries Climate Index. (n.d.). Home. Retrieved from https://actuariesclimateindex.org/home/

[8] Royal Commission into National Natural Disaster Arrangements. (2020). Australian Actuaries Climate Index: Some comments on extremes. Retrieved from https://naturaldisaster.royalcommission.gov.au/publications/exhibit-1-006003-shp5010010001-australian-actuaries-climate-index-some-comments-extremes

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