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Nino 3.4 sea temperature hits record as El Nino strengthens: Copernicus

By CAShorts DeskPublished Source: The Hindu, 12 October 2026, citing the EU's Copernicus Climate Change Service

Nino 3.4 sea temperature hits record as El Nino strengthens: Copernicus
Illustration (AI-generated)

The EU's Copernicus Climate Change Service said on 12 October 2026 that sea-surface temperature in Nino 3.4, a key El Nino monitoring region of the Pacific, reached an all-time high of 29.70°C in September, above the 1982/1983, 1997/1998 and 2015/2016 peaks. Copernicus added that it cannot yet call this El Nino the strongest on record.

Syllabus: Prelims · Geography; Prelims · Environment & Ecology; GS1 · World Physical Geography

Why it matters

A farmer who depends on seasonal rain is among the first to feel an El Nino: by shifting winds and rainfall around the globe, it raises the risk of drought in some regions and floods in others. It also adds natural heat on top of human-caused warming, so a strong El Nino tends to push the planet's average temperature to new highs; experts expect this one to help make 2027 a record year. How El Nino is measured matters as well. When the whole ocean is warmer than it used to be, a raw temperature record can make an event look stronger than it is, so Copernicus now adjusts for that background warming before calling any El Nino the strongest.

Prelims pointers

  • El Nino–Southern Oscillation (ENSO): El Nino is the warm phase, La Nina the cool phase; the Southern Oscillation is the Tahiti–Darwin see-saw in surface air pressure.
  • Nino 3.4 region: 5°N–5°S, 170°W–120°W in the central and eastern equatorial Pacific; the standard zone for declaring El Nino and La Nina.
  • Oceanic Nino Index (ONI): three-month running mean of the Nino 3.4 sea-surface temperature anomaly. Since February 2026 NOAA officially uses a Relative ONI, which subtracts the tropics' average anomaly.
  • ONI thresholds (the same for the Relative ONI): El Nino at +0.5°C or above, La Nina at −0.5°C or below, held for at least five consecutive overlapping three-month seasons.
  • During El Nino the easterly trade winds weaken, the thermocline deepens in the eastern Pacific and cold upwelling off Peru weakens.
  • Copernicus Climate Change Service (C3S): part of the EU's Copernicus Earth observation programme, implemented by the European Centre for Medium-Range Weather Forecasts for the European Commission.
  • Paris Agreement (2015, under the UNFCCC): hold warming well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C.
  • Paris 1.5°C limit: judged on long-term average warming, so a run of months above 1.5°C, as now, is a warning, not the breach itself.

Practise a UPSC-style question

With reference to the Oceanic Nino Index (ONI), consider the following statements:

1. It is the three-month running mean of the sea-surface temperature anomaly in the Nino 3.4 region.

2. It is computed and published by the Japan Meteorological Agency to declare El Nino and La Nina.

3. An El Nino episode is counted when it stays at or above +0.5°C for five consecutive overlapping three-month seasons.

Which of the statements given above is/are correct?

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1 and 3 only
  4. (d) 1, 2 and 3
Show the answer

Answer: (c) 1 and 3 only

1 is correct: the ONI averages the Nino 3.4 sea-surface temperature anomaly over three-month running periods. 2 is incorrect: the ONI is maintained by the US National Oceanic and Atmospheric Administration (NOAA); Japan's weather agency uses its own measure. 3 is correct: NOAA counts an El Nino episode when the ONI is at +0.5°C or above for at least five consecutive overlapping seasons (La Nina, −0.5°C or below). Since February 2026 NOAA officially declares El Nino on a Relative ONI, which subtracts the tropical-mean anomaly and keeps the same thresholds.

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