A very strong El Niño is forecast, and one study asks what it did to winter air last time

Published: 25 October 2026 | Author: Team JanVayu | Reading time: 5 min

NOAA's Climate Prediction Center issued its monthly ENSO discussion on 8 October 2026. El Niño is under an Advisory, it is strengthening, and a strong-to-very-strong event is likely through January to March 2027, with the chance staying above 83 per cent. The Center puts the chance of a historic event, one stronger than any since 1950 (a three-month index of +2.5°C or more), at 54 per cent for September to November, 83 per cent for October to December and 70 per cent for November to January. The Columbia IRI forecast of 19 October reports a weekly Niño 3.4 reading of +3.3°C, centred on 14 October. The Hindu's coverage this week focuses on the heat and the monsoon.

For an air-quality archive the question is what a large El Niño does to winter PM2.5 in India. One new paper bears on it, and its authors are careful about what it can and cannot say.

What the study found

Yadav, Beig and Kripalani, in Atmospheric Pollution Research (volume 17, article 103231, online 9 October 2026), looked at winter PM2.5, November to January, across two consecutive years in which emissions did not change appreciably.

In 2022-23, a La Niña winter, northern Indian cities were cleaner than their 2019 to 2022 average, by up to about 30 per cent in the paper's results. Peninsular cities were dirtier. The abstract describes year-to-year swings of up to 70 per cent with no significant change in emissions.
In 2023-24, an El Niño winter, the pattern reversed. The abstract describes the response as running from strong dispersion in one year to near-stagnation in the other.

The Times of India's report on the paper gives city figures that we have not been able to check against the full text, which sits behind a paywall. It says Jaipur recorded about 50 per cent more PM2.5 than its 2019 to 2022 average in the El Niño winter and Delhi a little over 10 per cent more, and that the authors tie the change to weaker winds over northern India and, for Jaipur, a larger role for surface pressure.

What the study does not say

The authors do not claim that El Niño worsens air in Delhi or north India in general. The Times of India reports their caution that the correlations show no direct causation and cannot be carried to other years. The abstract also says it is "premature" to attribute the two unusual years to climate change, and asks whether climate and air-pollution behaviour are becoming more erratic.

One more fact limits the comparison. The abstract calls the 2023-24 event "unusually short-lived". NOAA's present forecast is for a much stronger event that persists into early 2027. A study of one weak, brief El Niño winter and one La Niña winter says what two seasons did. Whether a very strong event produces the same stagnation is an open question.

What we will and will not say

JanVayu will not forecast Delhi's winter from an ENSO index. Winter PM2.5 depends on stubble burning, local emissions, boundary-layer depth, wind and the date the monsoon withdraws, and no study we have read quantifies how a +3°C El Niño changes the mix. NOAA is explicit that an event of this size makes El Niño-consistent impacts more likely but not guaranteed.

What the evidence supports is a reading rule for the coming months. If a city's PM2.5 this winter runs well above or below its recent average, check the weather before crediting or blaming a policy. Our September post, "Was it policy, or was it the wind?", explains how JanVayu separates weather from policy in its de-weathered series. The study adds a reason to take that rule seriously, because it measured swings of up to 70 per cent that no emission change explains.

NOAA's next ENSO discussion is due on 12 November 2026.

A very strong El Niño is forecast, and one study asks what it did to winter air last time

What the study found

What the study does not say

What we will and will not say

Sources