Since the number of species that the International Union for Conservation of Nature (IUCN) is increasing every year, one cannot accurately determine meaningful trends in the state of biodiversity for a country or the world over time.
To solve this issue, the IUCN established the Red List Index, which shows the trend in genuine changes in whether species have overall become more or less threatened. The index value ranges from 0 to 1, where 0 indicates all species are extinct, and 1 indicates that there is no concern of any species going extinct.
Over time, the general trend of the Red List Index Values across the world is decreasing. This is especially prominent in countries located near the equator. As of 2021, the country with the lowest Red List Index value (most threatened biodiversity) is Guam, with a value of 0.384, and the country with the highest Red List Index value (least threatened biodiversity) is Sweden, with a value of 0.992.
This overall downward trend indicates an overall decrease in biodiversity across the world through recent history.
Data Source: OECD. https://stats.oecd.org/Index.aspx?DataSetCode=RED_LIST