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La Nina and North India’s pollution
Context:
Recent research by the National Institute of Advanced Science (NIAS) highlights the complex relationship between climate change, La Niña, and air quality in India.
La Niña’s Impact on Delhi’s Pollution Levels:
- Late Retreat of Monsoon and Delayed La Niña:
- La Niña typically strengthens monsoons and brings dynamic atmospheric circulation that helps disperse pollutants.
- However, in 2024, the late retreat of the monsoon and delayed onset of La Niña raise concerns about higher pollution levels in Delhi and northern India during the winter.
- Meteorological Factors Worsening Pollution:
- The combination of high humidity, calm winds, and anti-cyclonic circulation in the post-monsoon period slows the dispersion of pollutants, leading to higher levels of PM2.5 and PM10.
- The neutral atmospheric conditions caused by the delayed La Niña reduce surface wind speeds, trapping pollutants near the ground.
- Extended Stubble Burning Season:
- La Niña extends the monsoon, delaying crop harvesting in Punjab and Haryana, which pushes stubble burning into November.
- Combined with colder weather, pollutants from stubble burning remain trapped closer to the ground, exacerbating Delhi’s pollution.
- Temperature Inversions:
- Cooler temperatures during La Niña cause temperature inversions, where cold air and pollutants near the surface are trapped by a warmer air layer above.
- This prevents the dispersion of pollutants, leading to a build-up of PM2.5 and PM10.
- Prolonged Smog Episodes:
- If La Niña sets in during December or January 2024, stronger winds may slightly improve air quality later in the winter.
- However, a longer and more severe winter could limit vertical atmospheric mixing due to a lower inversion layer, resulting in prolonged smog episodes.
Impacts of La Niña:
Weather Impacts
- Increased Rainfall: Southeast Asia, Australia, India (flooding).
- Drought: Southern U.S., parts of South America and Africa.
- Hurricanes: More intense Atlantic hurricanes, reduced Pacific cyclones.
- Colder Winters: Northern U.S. and northern Asia.
- Warmer Temperatures: Southern U.S. and southern Africa.
Non-Weather Impacts
- Agriculture: Crop failures and food price increases.
- Fisheries: Improved fish stocks in some regions (e.g., Peru).
- Energy: Droughts reduce hydropower; hurricane disruptions in oil production.
- Wildfires: Increased risk in drier regions.
- Health: Rise in waterborne and vector-borne diseases.
- Migration: Displacement due to extreme weather events.
- Economic Instability: Resource competition and potential unrest.
- Infrastructure Damage: Flooding and repair costs; disrupted shipping routes.
Conclusion:
The Need for a Shift in Policy:
Policymakers should not focus solely on PM10 emissions, which are primarily caused by dust, but instead prioritise PM2.5, a more harmful pollutant primarily from fossil fuel combustion. There is a need to transition from an emission-centric approach to one that incorporates larger meteorological and climatological factors. Such an approach would help in developing more effective airshed-based strategies for improving air quality.