The Actuaries Climate Index (ACI), which measures changes in extreme weather conditions and sea levels, was recently updated. It shows an increase in fall 2025 compared with the previous summer.
The ACI’s five-year moving average stood at 1.42, compared with the baseline average of zero during the reference period from 1961 to 1990.
In the previous update, released in March 2026 for the summer 2025 period, the ACI stood at 1.41.
“Changes in temperature indices (T10 and T90) were the primary drivers of the increase in the composite index,” states the organization responsible for calculating the ACI.
Comparison with fall 2020
The ACI’s five-year moving average was revised following the addition of the seasonal data for fall 2025. That seasonal value reached 1.79 for Canada and the United States.
The moving average is calculated over five years and updated quarterly. The fall 2025 data replaces the fall 2020 data in the moving average. In 2020, that seasonal value stood at 1.30, and the five-year index was 1.23.
Combination
Quarterly seasonal data are collected to determine the value of the Actuaries Climate Index. It combines the variables that have the greatest impact on the population and the economy: high and low temperatures, heavy rainfall, drought, high winds and sea level.
For the sea level sub-index, the five-year moving average for Canada and the United States stood at 2.81 in fall 2025, compared with 2.78 in the previous quarter. The fall 2025 seasonal value, which reached 3.55, replaces the fall 2020 value of 3.01 in the calculation of that moving average.
