TEMPERATURE ANOMALIES IN 2024
NEWS: The year 2025 is witnessing a confused El Niño Southern Oscillation (ENSO) state, with warm SST anomalies emerging in the far eastern tropical Pacific and cold SST anomalies in the central-western tropical Pacific.
WHAT’S IN THE NEWS?
Non-Emergence of La Niña
• At the beginning of 2024, cold Sea Surface Temperature (SST) anomalies were forecasted in the far eastern tropical Pacific Ocean, suggesting the onset of a La Niña event.
• However, as the year progressed, these cold SST anomalies shifted westward towards the international dateline.
• Simultaneously, warm SST anomalies appeared in the far eastern Pacific by early summer 2024, leading to the failure of the expected La Niña event.
Cause of La Niña’s Failure
• The failure of the strong La Niña forecasted for 2024 is likely attributed to the ENSO Transition Mode (ETM), which induced wind anomalies in the tropical Pacific Ocean.
• ENSO (El Niño-Southern Oscillation) is a climate phenomenon that includes two opposite phases:
• El Niño (warm phase) – Characterized by warm SST anomalies in the central and eastern Pacific.
• La Niña (cold phase) – Characterized by cold SST anomalies in the eastern and central Pacific.
• In 2024, an unusual pattern of cold SST anomalies west of warm SST anomalies in the far eastern Pacific persisted, disrupting the expected La Niña event.
Dateline El Niño or Central Pacific El Niño
• In recent decades, a reverse pattern has become more common, where warm SST anomalies form around the dateline while cold SST anomalies develop near the Galápagos Islands in the eastern Pacific.
• This variation is referred to as a Dateline El Niño or Central Pacific El Niño.
• El Niño "flavours" refer to the variations in El Niño patterns where:
• Warm SST anomalies may appear in the eastern Pacific or
• Warm SST anomalies may form in the central Pacific, resembling the typical La Niña pattern.
Anomalies in Wind Patterns
• In 2024, strong easterly wind anomalies were observed in the central-western tropical Pacific.
• At the same time, westerly wind anomalies were recorded in the far eastern tropical Pacific.
• These unusual wind patterns played a crucial role in disrupting the predicted La Niña event and influencing global weather conditions.
Sea Surface Temperature (SST) Anomalies
Definition of SST Anomalies
• SST anomalies refer to temporary deviations from the long-term average SST in a particular region.
• These anomalies help identify whether the ocean surface is warmer or cooler than usual at a given time.
• Types of SST anomalies:
• Positive SST anomalies → Warmer-than-average temperatures.
• Negative SST anomalies → Cooler-than-average temperatures.
Role of ENSO in SST Anomalies
• The El Niño-Southern Oscillation (ENSO) is a key driver of SST anomalies.
• ENSO operates in irregular cycles of 3–6 years, causing fluctuations in Pacific Ocean temperatures.
• SST anomalies associated with ENSO influence global weather patterns, affecting rainfall, storms, and temperature extremes worldwide.
Measuring Anomalous Temperature Patterns
• SST anomalies are calculated by comparing current sea surface temperatures to long-term climatological averages.
• The commonly used reference period for SST anomaly calculations is 1991-2020.
Long-Term Changes in SST
• Between the late 19th century (1880-1900) and recent years (2019-2023):
• The global average SST over the extrapolar ocean (60°S–60°N) has increased by 0.9°C.
• Between 1980 and 2023:
• The increase in SST was around 0.6°C.
Fastest-Warming Ocean Regions
• Certain regions have experienced rapid warming over time:
• Arctic Ocean – Barents Sea and Kara Sea.
• Baltic Sea and Black Sea – Significant warming trends observed.
• North Pacific – Extra-tropical regions warming at an accelerated pace.
Exception: Cooling in the North Atlantic
• The North Atlantic Ocean, particularly the region south of Greenland and Iceland, remains one of the few areas globally to have cooled over long timescales.
Importance of Studying SST Anomalies
Climate Variability and Predictability
• SST anomalies drive tropical climate variability, including ENSO events (El Niño and La Niña).
• These anomalies influence seasonal climate patterns and extreme weather events.
Role in Weather Forecasting
• SST anomalies are critical for long-range weather forecasting, particularly in:
• Subseasonal forecasts (up to 30 days).
• Seasonal forecasts (several months ahead).
Impact on Atmospheric Circulation
• SST anomalies alter atmospheric circulation, changing global wind patterns and influencing weather systems across continents.
Influence on Rainfall Patterns
• Positive SST anomalies (warmer waters) → Increased evaporation → Heavy rainfall and potential flooding in some regions.
• Negative SST anomalies (cooler waters) → Suppressed evaporation → Drought conditions in affected areas.
Contribution to Extreme Weather Events
• SST anomalies fuel hurricanes, cyclones, and typhoons, as warm ocean temperatures provide energy for these storms.
Ocean-Atmosphere Interactions
• The ocean and atmosphere continuously exchange heat, gases, and momentum.
• Understanding SST anomalies helps scientists study climate interactions, including ocean currents and global heat distribution.
Monitoring Marine Heatwaves and Oceanic Features
• SST anomalies are used to track marine heatwaves, ocean fronts, and upwelling zones, which are vital for marine ecosystems and fisheries.
Sea Surface Temperature (SST) – Measurement and Importance
Definition of SST
• Sea Surface Temperature (SST) refers to the temperature of the ocean’s uppermost layer, usually the top few meters.
• This layer is in direct contact with the atmosphere, making SST a crucial factor in climate studies.
Difference Between OMT and SST
• Ocean Mean Temperature (OMT) – Measures ocean temperature down to the 26°C isotherm, covering depths of 50-100 meters.
• SST – Measures temperature only at the surface.
SST Variations Across Latitudes
• Warmest SSTs are found near the equator.
• Coldest SSTs occur in the polar regions (Arctic and Antarctic).
Methods of Measuring SST
• Satellite Sensors:
• Advanced High-Resolution Radiometer (AVHRR) on NOAA’s Polar-Orbiting Environmental Satellites (POES).
• Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites.
• Buoys and Ships: Floating instruments record SST in real time.
• Ocean Reference Stations: Fixed installations provide continuous SST data.
Importance of SST Monitoring
• SST data is essential for climate monitoring and forecasting.
• SST patterns influence:
• Global atmospheric circulation.
• Rainfall patterns.
• Frequency and intensity of tropical cyclones.
• Long-term climate change assessments.
Causes of SST Rise
Global Warming
• Increased greenhouse gas emissions trap heat, raising global temperatures, including ocean temperatures.
Ocean Heat Absorption
• The oceans absorb over 90% of the excess heat caused by human-induced climate change, leading to a gradual rise in SST.
Ocean Acidification
• Oceans act as carbon sinks, absorbing CO₂, leading to acidification and contributing to warming of surface waters.
Albedo Effect and Ice Melt
• Melting polar ice reduces Earth's reflectivity (albedo), causing oceans to absorb more heat, further increasing SST.
Source: https://www.theweek.in/news/india/2025/03/20/india-fifth-in-asia-to-experience-temperature-anomalies-maharashtra-mizoram-worst-hit.html