Red List of IUCN is known as

Correct — option (4), Barometer of Life.

The IUCN describes its Red List of Threatened Species as "a barometer of life". On IUCN's page for the list, that heading introduces the Red List as a critical indicator of the health of the world's biodiversity.

A barometer measures air pressure, and a change in its reading signals a change in the weather. The Red List works the same way for nature: shifts in species' extinction-risk categories show whether biodiversity is improving or declining.

IUCN's Director General used the phrase again in October 2024, as the Red List marked 60 years since its launch in 1964.

The idea to remember: the IUCN Red List is the "barometer of life", tracking the extinction risk of animal, fungus and plant species.

Why the others are wrong

• (1)
  Mirror of Life — IUCN's own phrase for the Red List is "a barometer of life", not "Mirror of Life".

  The barometer image stresses measurement of change. The Red List is reassessed and updated, so it records change in species' extinction risk over time.

• (2)
  Life Thermometer — A thermometer measures temperature, and IUCN's chosen instrument for the Red List is the barometer, not the thermometer.

  IUCN does run a trend measure built on the list: the Red List Index, which shows trends in overall extinction risk for species and which governments use to track progress on reducing biodiversity loss.

• (3)
  Hydrometer of Earth — A hydrometer measures the relative density of liquids, such as milk or battery acid. IUCN's description of the Red List uses a barometer, not a hydrometer.

  The barometer metaphor refers to reading the state of biodiversity, not any property of water or of the Earth's liquids.

According to IUCN, the Red List of Threatened Species is the world's most comprehensive information source on the global extinction risk status of animal, fungus and plant species.

Each assessed species is placed in one of nine categories: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern, Data Deficient and Not Evaluated.

Vulnerable, Endangered and Critically Endangered species are considered threatened with extinction. Because species are reassessed over time, a move between categories shows whether their prospects are improving or worsening.

Key facts

• IUCN describes the Red List of Threatened Species as a barometer of life and a critical indicator of the health of the world's biodiversity.
• The IUCN Red List was launched in 1964; IUCN marked its 60th anniversary in October 2024.
• The Red List has nine categories, running from Extinct to Not Evaluated.
• Vulnerable, Endangered and Critically Endangered species are considered threatened with extinction.
• After its 28 October 2024 update, the Red List included 166,061 species, of which 46,337 were threatened.

Common traps

• The Red List's nickname uses a barometer, which measures pressure. Thermometer and hydrometer sound similar as instruments but are not the image IUCN uses.
• "Threatened" is a group, not a single category: it covers Vulnerable, Endangered and Critically Endangered. Near Threatened sits outside it despite its name.
• Data Deficient means a species was assessed but information was inadequate to judge its risk. Not Evaluated is the category for species not yet assessed.

UnlockIAS will link similar questions from RAS Pre 2013 here once that paper is published on this site.

• practice — not a real PYQ

  Which of the following IUCN Red List categories is not counted among species threatened with extinction?

  • (a)Vulnerable
  • (b)Endangered
  • (c)Near Threatened
  • (d)Critically Endangered
  Answer(3) — IUCN counts only Vulnerable, Endangered and Critically Endangered as threatened, so Near Threatened falls outside the group. Options (1), (2) and (4) are the three threatened categories.
• practice — not a real PYQ

  In the IUCN Red List, a species that has been assessed but lacks adequate information to judge its extinction risk is placed in which category?

  • (a)Not Evaluated
  • (b)Data Deficient
  • (c)Least Concern
  • (d)Near Threatened
  Answer(2) — Data Deficient is used when information is inadequate for an assessment of extinction risk. Option (1) is for species not yet assessed; options (3) and (4) are given only when there is enough information to judge the risk.