This finding is based on a statistical analysis of temperature data collected since the seventeenth or eighteenth century at 17 sites in Europe. The analysis shows that the chance of a given year being warmer than average started to rise at all sites at that time. The scientists compared the results of their analysis with possible causes of a change to the climate. The causes considered were changes of ocean circulation, loss of sea ice from the Arctic Ocean, and a reduction in particle emissions in Europe.

Based on this comparison, they were able to show that loss of sea ice, possibly linked to particle emission reductions, was a possible cause of the change that was detected. They note that sea ice loss makes the Earth darker, which allows more heat to be absorbed from the Sun, making the Earth warmer. This causes more sea ice to melt and might ultimately result in a complete loss of sea ice in the Arctic Ocean during the summer months.

Link to the article: Skewness of Temperature Data Implies an Abrupt Change in the Climate System Between 1985 and 1991 - Skelton - 2020 - Geophysical Research Letters – Wiley Online Library

Time series of mean annual temperature data. Temperature data (gray lines) with 11‐year moving averages (black lines) are shown for stations and time intervals listed in Table 1. Note that the length of the y axis (mean annual temperature) is the same (6°C) for all plots but values differ between plots. Also, note that the x axis is from 1650 to 2020 for the Hadley Centre, 1700 to 2020 for Uppsala, and 1750 to 2020 for all other stations.