Based on the new methodology and the data through fall 2018, the ACI's five-year moving average increased between winter and fall 2018 from 0.91 to 1.03, the highest level over the period studied, January 1961 through November 2018. The increasing value reflects continued deviation of climate extremes and sea level from historical levels for the two countries.
As part of the application of the new methodology, the working group also restated past ACI results (see accompanying chart). The restatement produces slightly lower index values over the past 25 years but does not affect previously reported long-term trends, says Collins.
The Actuaries Climate Index is based on analysis of seasonal data from neutral, scientific sources for the six different index components collected since 1961. The index measures changes in extremes of high and low temperatures, high winds, heavy precipitation, and drought, as well as changes in sea level, expressed in units of standard deviations from the mean for the 30-year reference period of 1961 to 1990 for the United States and Canada combined and by region.
The index, sponsored by the American Academy of Actuaries, the Canadian Institute of Actuaries, the Casualty Actuarial Society, and the Society of Actuaries, is designed to provide actuaries, public policymakers, and the general public with objective data about changes in the frequency of extreme climate events over recent decades.
Updated values are posted quarterly on ActuariesClimateIndex.org as data for each meteorological season becomes available. The organizations are also developing a second index, the Actuaries Climate Risk Index, to measure correlations between changes in the frequency of extreme events and economic losses, mortality, and injuries.