The World Meteorological Organization (WMO) recently issued an update indicating a significant possibility of a La Niña event developing later in 2024, marking a crucial transition in global climate dynamics. As of mid-August, conditions in the Pacific Ocean have been neutral, neither influenced by El Niño nor La Niña, part of the larger El Niño–Southern Oscillation (ENSO) phenomenon. However, this neutrality may soon give way to La Niña, with a 55% likelihood between September and November 2024, increasing to 60% in the subsequent months. This transition may have profound consequences on global weather patterns, ecosystems, and economies, especially considering the extreme impacts of previous La Niña episodes.
Understanding La Niña: A Crucial Climate Phenomenon
To comprehend the possible impact of an emerging La Niña, it is essential to first understand what it is and how it contrasts with El Niño. Both are phases of the ENSO, a naturally occurring cycle of ocean and atmospheric patterns in the tropical Pacific Ocean. La Niña is characterized by cooler-than-average sea surface temperatures in the central and eastern equatorial Pacific, which triggers a shift in global atmospheric circulation.
During La Niña, cooler ocean waters amplify the trade winds, which blow from east to west across the equatorial Pacific. These winds push warm surface waters towards the western Pacific, causing upwelling of colder water from the ocean’s depths in the eastern Pacific. This process affects weather patterns globally, leading to phenomena such as stronger monsoon seasons, increased rainfall in some regions, and more severe droughts in others.
In contrast, El Niño represents the opposite phase, where warmer sea surface temperatures in the central and eastern Pacific disrupt normal weather patterns, often bringing heavy rainfall and flooding to typically dry areas while causing droughts in normally wetter regions.
The current ENSO-neutral conditions observed throughout mid-2024 have allowed for a balance in global weather patterns, but the looming potential of La Niña threatens to tip this equilibrium in dramatic ways.
Indicators of La Niña Formation in 2024
The recent WMO report provides several indicators that La Niña conditions may soon develop. Since August 2024, the equatorial Pacific Ocean has exhibited cooling trends, particularly in the eastern Pacific, where sea surface temperatures have ranged from 0.3°C below to 0.6°C above normal. Although these temperature anomalies remain within the neutral range, subsurface cold anomalies have been observed, particularly in the eastern and central Pacific, suggesting that the region is preparing for a transition.
Additionally, atmospheric patterns are consistent with the early stages of La Niña development. The trade winds, which are critical to maintaining La Niña conditions, have been close to their normal strength across the Pacific, and convection patterns (the rising of warm air and subsequent precipitation) are showing signs of transitioning to a La Niña-like state.
The WMO also highlights that the Equatorial Southern Oscillation Index (ESOI), which measures differences in sea-level pressure between the central Pacific and Indonesia, has remained within the neutral range but is trending toward values that could support La Niña conditions. All of these indicators suggest that while the Pacific is currently neutral, it is poised for a significant shift.
Global Impacts of La Niña
The development of a La Niña event has far-reaching implications, affecting weather patterns across continents. Historically, La Niña events have led to severe weather extremes, from floods to droughts, which in turn disrupt agriculture, water supply, ecosystems, and even economies.
1. Asia-Pacific Region
One of the most immediate impacts of La Niña is felt in the Asia-Pacific region, where the phenomenon typically strengthens the monsoon season. Countries such as India, Bangladesh, and Indonesia may experience heavier rainfall and an increased risk of flooding. While this can replenish water supplies and aid in crop production, excessive rainfall can lead to destructive floods, landslides, and infrastructure damage. The Indian subcontinent, in particular, relies on a balanced monsoon season for agricultural productivity, and any deviation due to La Niña can have significant consequences for food security.
In Southeast Asia, countries like the Philippines and Vietnam may face more intense typhoon seasons, as La Niña tends to create favorable conditions for the development of stronger tropical cyclones in the western Pacific. This increases the likelihood of devastating storms, which bring destruction to coastal regions and often result in the displacement of thousands of people.
2. Australia
Australia is one of the regions most directly affected by La Niña, as it typically leads to above-average rainfall, particularly in the eastern parts of the country. During past La Niña events, Australia has experienced severe flooding, most notably during the 2010–2011 La Niña, which caused widespread floods in Queensland. Conversely, La Niña brings relief from droughts, as its wetter conditions can help refill reservoirs and support agriculture, especially in regions that have been experiencing prolonged dry spells.
The risk of flooding, however, presents a serious challenge. If La Niña intensifies in late 2024, parts of Australia may face extreme weather, particularly as the country emerges from its dry winter season.
3. North and South America
La Niña often brings contrasting impacts to the Americas. In the United States, it typically results in cooler and wetter conditions in the Pacific Northwest, while the southern states experience drier and warmer weather. This has significant implications for agriculture, particularly in states like Texas and California, where drier conditions can exacerbate already persistent droughts, leading to reduced crop yields and increased wildfire risks.
Conversely, in South America, countries such as Brazil, Argentina, and Peru may experience above-average rainfall, particularly in the northern and western parts of the continent. While increased rainfall can benefit agriculture, there is also a heightened risk of flooding, particularly along major river systems such as the Amazon.
4. Africa
In East Africa, La Niña is typically associated with drier-than-average conditions, which can exacerbate droughts in already arid regions. This is particularly concerning for countries like Somalia, Ethiopia, and Kenya, which have faced repeated cycles of drought in recent years. A 2024 La Niña event could worsen food insecurity and lead to increased reliance on international aid.
On the other hand, southern Africa often benefits from La Niña, as it brings increased rainfall, which can support agricultural production and replenish water resources in countries like Zambia, Zimbabwe, and South Africa.
Preparing for the Transition
Given the potential impacts of a La Niña event, governments, industries, and communities around the world must begin preparing for the possibility of severe weather disruptions. Early warning systems, disaster preparedness plans, and adaptive strategies for agriculture and water management will be critical in mitigating the negative effects of La Niña.
The WMO and national meteorological services will continue to monitor the situation closely, providing updates as the likelihood of La Niña increases. Communities in high-risk areas should remain vigilant and prepare for possible disruptions to agriculture, infrastructure, and daily life.
Conclusion
The potential emergence of a La Niña event in late 2024 is a reminder of the significant impact that the ENSO cycle can have on global weather patterns. While the exact intensity and duration of this La Niña are yet to be determined, the historical effects of similar events suggest that the world could face a range of weather extremes in the coming months. From increased rainfall and flooding in some regions to droughts and wildfires in others, the effects of La Niña will be felt across continents. As the world braces for these changes, early action and preparedness will be key to minimizing the damage and safeguarding vulnerable communities.
