The International Union for Conservation of Nature's Red List of Threatened Species (IUCN Red List) released assessments on 150,300 species, of which 42,100 are threatened (listed as Critically Endangered, Endangered, or Vulnerable). This covers 41% of amphibians, 37% of sharks and rays, 36% of hermatypic corals, 34% of coniferous trees, 27% of mammals, and 13% of birds. Based on species' quantity, distribution, density, and research, the IUCN classifies species threat into nine protection levels: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern, Data Deficient, and Not Evaluated. Of these levels, Critically Endangered, Endangered, and Vulnerable are listed on the Red List for extinction risk.

The OECD evaluates the threat level of birds, mammals, and vascular plants in its member states according to IUCN-specified criteria. The top five countries with the highest threatened levels are shown in the figure above. The Czech Republic is the country where birds are most threatened (48.52% of total known bird species), followed by Iceland (44%), Estonia (40.6%), Denmark (34.86%), and Switzerland (34.63%). Costa Rica has the least number of threatened birds, with 3.37% among all member states. The top five countries with the most threatened mammals are Slovenia (38.2%), Switzerland (36.56%), Germany (36.45%), Australia (28.38%), and Mexico (26.6%), while Ireland (1.75%) has the least number of threatened mammals. The top five countries with the most threatened vascular plants are the Czech Republic (40.25%), Austria (33.39%), Germany (32.75%), Luxembourg (26.76%), and Switzerland (25.64%). Turkey (1.62%) has the least number of threatened vascular plants.

Despite being rich in ecological resources and breeding various species and endemic species thanks to its unique geographical location, Taiwan is not included in the list. However, the Formosan clouded leopard went extinct, with the leopard cat, the Ryukyu flying fox, the Formosan black bear, the green sea turtle, the eastern grass owl, and the Taiwan salamander entered the list as Endangered, reflecting the impact of global warming over time. Rising temperatures are bound to disrupt Taiwan's ecosystem. Striking a balance between economic development and natural ecology is the biggest challenge for the government.