Why La Nina did not bring down Temperature?

Learn about the La Niña effect, its causes, impact on global weather patterns, influence on monsoons, and its effects on agriculture, climate, and economies worldwide.

Table of Contents

Context: The Copernicus Climate Change Service (C3S) reported that January 2025 was the hottest January on record.

What is La Niña Affect?

La Nina is one of the three phases of the El Nino-Southern Oscillation (ENSO), a climate phenomenon that influences global weather patterns.

ENSO involves periodic changes in the sea surface temperatures and atmospheric conditions in the Pacific Ocean.
During La Niña, the sea surface temperatures in the central and eastern equatorial Pacific Ocean become unusually cold.
This is caused by stronger-than-normal trade winds, which blow from east to west across the Pacific.
These winds push warm surface water toward the western Pacific (near Asia and Australia), allowing colder water from the ocean depths to upwell (rise) to the surface in the eastern Pacific near South America.
La Niña events typically last 9–12 months, though they can persist for up to 2 years in some cases.

Phases of ENSO

Neutral Phase
- The eastern Pacific Ocean (near South America) is cooler than the western Pacific (near Indonesia).
- Trade winds push warm surface water towards Indonesia, allowing cooler waters from below to rise.
El Niño (Warm Phase)
- Trade winds weaken, reducing the movement of warm waters toward Indonesia.
- As a result, the eastern Pacific becomes warmer than usual.
- This generally leads to higher global temperatures.
La Niña (Cool Phase)
- Trade winds become stronger, pushing larger amounts of warm water westward.
- This causes colder-than-normal waters in the eastern Pacific.
- Typically results in lower global temperatures.

La Niña’s General Effects on Temperature

El Niño increases global temperatures, while La Niña cools them.
However, regional effects vary, and some areas may experience both warming and cooling.

Why Did La Niña Not Cool Temperatures in January 2025?

Weak La Niña Development

Not all La Niña phases have the same intensity.
The ongoing La Niña cycle is weak, which reduces its overall cooling effect.

Increased Greenhouse Gas (GHG) Emissions

Despite La Niña, the rate of increase in atmospheric carbon remained high in 2024 and January 2025.
Normally, a strong La Niña brings more rain, leading to increased plant growth.
- More plant growth means higher carbon absorption, reducing heat-trapping gases.
- However, this effect was not strong enough this time.

Decline in Aerosol Concentration

Aerosols (suspended particles in the atmosphere) have a cooling effect by:
- Scattering solar radiation back into space.
- Influencing cloud formation, which affects how much sunlight is absorbed or reflected.
Due to clean air policies in some regions, aerosol concentrations have decreased.
- This weakened the cooling effect, allowing temperatures to remain high.

Fact

This decade began with three consecutive La Niña events (2020-2022), a rare occurrence known as Triple Dip La Niña (the first since 1998-2001), followed by an El Niño in 2023.

Impacts of La Niña on Global Climate

The effects of La Niña vary globally but typically include:

Weather Patterns

Asia and Australia: Higher-than-average rainfall, risk of flooding, and stronger monsoon seasons.
South America (Pacific Coast): Drier weather, drought conditions.
North America:
- Cooler and wetter winters in the northern U.S. and Canada.
- Warmer and drier conditions in the southern U.S.
Africa: Wetter conditions in eastern Africa but drought in southern Africa.

Hurricanes and Cyclones

La Niña typically increases the frequency and intensity of hurricanes in the Atlantic Ocean due to reduced vertical wind shear.

Global Climate Impact

It can lead to temporary global cooling, as the colder Pacific waters influence global temperatures.

Climate Change and La Nina

Climate scientists highlight that global warming is altering natural phenomena like ENSO.
La Niña events, once relatively predictable, are now occurring with greater frequency and intensity.
Despite La Niña’s cooling influence, its effects are increasingly overshadowed by long-term global warming trends.
The interaction between La Niña and global warming remains under study, but early research suggests increasing erratic behaviour.
This could lead to unexpected droughts, floods, and heatwaves in regions previously unaffected by such extremes.

India and La Niña (2025): Localized Impacts

Colder and Wetter Winters

Northern and northwestern states like Punjab, Haryana, and Rajasthan may experience prolonged cold spells and dense fog.
Disruptions to daily life and transportation are likely.
Cooler temperatures can benefit crops like wheat, but extreme cold may negatively impact human health and productivity.

Enhanced Monsoon Activity

Above-average monsoon rains are expected, extending into late September or October.
Benefits include improved water reservoirs and hydroelectric projects.
However, the risk of flooding increases in vulnerable regions such as Assam, Bihar, and parts of Maharashtra.

Impact on Agriculture

Heavier rains can boost rabi (winter) crop production by improving soil moisture.
Excess rainfall may cause waterlogging in key rice and wheat-growing areas, potentially damaging crops and delaying harvests.

Water Resource Management

La Niña could help replenish groundwater levels and reservoirs.
However, unplanned water discharge during heavy rains may trigger flooding in urban areas.
Coastal cities like Mumbai and Chennai need robust disaster management systems to prevent waterlogging and disruptions.

Public Health Challenges

Extended rains and cooler temperatures may increase waterborne diseases like cholera and dengue, especially in densely populated urban areas.
Healthcare preparedness and public awareness campaigns will be essential to manage these health risks.

Impact of La Niña on Air Quality

Delayed Onset Exacerbates Pollution: due to the late arrival of La Niña, there is a prolonged period of stagnant surface winds, particularly in autumn and early winter.
- This leads to a buildup of pollutants, such as PM2.5 and PM10, near the surface, worsening air quality.
Extended Severe Winters: There may be stronger winds, fewer clouds, a reduction in pollutant accumulation and slightly improved air quality in late winter.
- However, a longer and more severe winter could lower the inversion layer, limiting vertical air mixing and keeping pollutants trapped.
Delayed Monsoon Withdrawal: La Niña’s influence on monsoons can also cause a delayed monsoon retreat, leading to extended high humidity and calm winds.
- This combination reduces atmospheric mixing, trapping pollutants near the surface and increasing levels of particulate matter (PM2.5 and PM10) in the air.
- These factors, coupled with local emissions and pollution from neighbouring regions (such as stubble burning from Punjab and Haryana) worsen air quality during the pre-winter period.
Impacts on Different Regions: While La Niña improves air quality in northern India by dispersing pollutants, it can worsen conditions in other regions, particularly peninsular India, by increasing PM2.5 levels by up to 20%.
- Early or late arrival of La Niña can have differing impacts depending on geographic location.