How El Niño Influences Ocean Temperatures and Marine Heatwaves Around the World

Scientists Measure Ocean Temperature Around the World

(Starts: 00:01:46)

Understanding changes in ocean temperature depends on the ability to measure conditions across vast and remote areas of the world's oceans.

Historically, ocean temperature measurements were collected by ships travelling established routes. These observations provided valuable information but left significant gaps across large regions of the ocean. Scientists could only build a partial picture of how temperatures were changing because data collection depended on where ships happened to travel.

A major breakthrough came in 1981 with the introduction of satellite observations. Satellites enabled scientists to monitor surface ocean temperatures across the entire globe on a continuous basis. For the first time, researchers could observe large-scale patterns and changes occurring across entire ocean basins rather than relying on isolated measurements.

Ocean observations moved from scattered ship measurements to truly global coverage through satellites and autonomous monitoring systems.

Monitoring below the ocean surface requires additional technologies. One of the most important tools is the global network of Argo floats. These autonomous instruments move up and down through the water column, collecting information on temperature, salinity and other ocean properties. Standard Argo floats measure conditions down to around 2,000 metres, while newer Deep Argo systems can reach depths of 6,000 metres.

Research vessels also continue to play a vital role. Scientists repeatedly survey specific routes across the ocean to create long-term records of changing conditions. These measurements help monitor major ocean circulation systems and validate observations gathered from satellites and autonomous platforms.

Together, these technologies provide a comprehensive picture of the global ocean, allowing scientists to track warming trends and detect emerging climate anomalies.

How Much Have Ocean Temperatures Increased Since Pre-Industrial Times?

(Starts: 00:04:05)

The world's oceans absorb vast amounts of heat from the atmosphere and play a central role in regulating Earth's climate.

According to long-term observations discussed in the transcript, average global ocean temperatures have increased by approximately 1°C over the past hundred years. While a rise of one degree may sound modest, it represents a significant amount of additional heat stored throughout the global ocean.

Global ocean temperatures have risen by around 1°C over the last century, with some regions warming faster than others.

Importantly, ocean warming is not uniform.

The North Atlantic has experienced particularly rapid warming relative to the global average. By contrast, the Southern Ocean surrounding Antarctica has warmed more slowly. These regional differences occur because ocean currents, atmospheric conditions and patterns of heat transport vary across different parts of the world.

Even relatively small changes in average ocean temperature can have far-reaching consequences. Warmer oceans influence marine ecosystems, weather patterns and the exchange of heat between the ocean and atmosphere. They also create conditions that can make marine heatwaves more likely and more intense when additional climate drivers come into play.

These long-term warming trends provide the backdrop against which shorter-term climate phenomena such as El Niño operate.

Why Were Marine Heatwaves So Extreme in 2023?

(Starts: 00:05:14)

The year 2023 saw exceptional temperature extremes across both land and ocean environments.

On land, heatwaves affected multiple continents, including North America, North Africa, Europe and parts of Asia. Similar extremes were observed across large areas of the ocean.

One of the most notable marine heatwaves developed in the North Atlantic Ocean around the British Isles during late spring and early summer. In some locations, ocean temperatures rose as much as 5°C above average seasonal conditions. Similar marine heatwaves occurred in parts of the Mediterranean Sea and in the western Pacific, including the Sea of Japan and the Kuroshio Extension region.

Some areas of the North Atlantic experienced ocean temperatures up to 5°C above average.

These events were linked to unusual atmospheric circulation patterns. A major factor was the behaviour of the jet stream, a fast-moving current of air high in the atmosphere. During 2023, parts of the jet stream became locked into relatively stationary wave patterns. Instead of moving weather systems along, these blocked patterns allowed extreme conditions to persist over the same regions for extended periods.

This helped create simultaneous temperature extremes across large areas of the Northern Hemisphere, affecting both the atmosphere and the ocean.

What Is El Niño and Why Does It Increase Global Temperatures?

(Starts: 00:09:09)

El Niño is one of the most important natural climate phenomena on Earth. It occurs irregularly, typically every two to seven years, and involves interactions between the tropical Pacific Ocean and the atmosphere above it.

Under normal conditions, a large pool of very warm water accumulates in the western Pacific Ocean. Temperatures within this warm pool can reach around 30°C. During an El Niño event, this body of warm water spreads eastward across the Pacific towards the coast of South America.

El Niño is the most pronounced mode of climate variability after the seasonal cycle itself.

This redistribution changes how heat is stored and exchanged within the climate system.

Rather than remaining concentrated in one region, the warm water becomes spread over a broader area of ocean surface. This increases the transfer of heat from the ocean to the atmosphere, contributing to higher global average temperatures.

The transcript highlights that several previous record-breaking warm years, including 1998 and 2016, coincided with strong El Niño events. This demonstrates how the phenomenon can amplify existing warming trends and push global temperatures beyond previous records.

Although El Niño is a natural feature of the climate system, its effects are increasingly occurring against a background of long-term global warming.

How Does El Niño Affect Weather, Fisheries and Coral Reefs?

(Starts: 00:11:18)

The impacts of El Niño extend far beyond the tropical Pacific Ocean.

One of its most significant effects is the alteration of global rainfall patterns. Regions along the west coast of South America, particularly Peru, often experience intense rainfall and flooding associated with strong convective storms. Meanwhile, areas including Indonesia and parts of East Asia tend to become drier than average.

El Niño alters rainfall patterns worldwide while disrupting marine ecosystems in the eastern Pacific.

These atmospheric changes influence agriculture, water resources and ecosystems across multiple continents.

Marine ecosystems are also heavily affected.

Under normal conditions, cold nutrient-rich water rises to the surface in parts of the eastern Pacific through a process known as upwelling. This nutrient supply supports highly productive marine food webs and important fisheries. During El Niño, the arrival of warm surface water suppresses this upwelling process.

As nutrient availability declines, fisheries can be severely disrupted. Species distributions may change and ecosystem productivity can decrease.

Coral reefs are also vulnerable. Elevated ocean temperatures associated with El Niño have been linked to major coral bleaching events across tropical reef systems. When temperatures remain unusually high for prolonged periods, corals can lose the symbiotic organisms that provide them with energy and colour, increasing the risk of widespread reef degradation.

What Is La Niña and Why Did Temperatures Rise So Quickly After It Ended?

(Starts: 00:16:06)

La Niña is often described as the opposite phase of El Niño.

Instead of warmer-than-average conditions developing in the eastern tropical Pacific, La Niña is characterised by a cold temperature anomaly in that region. The resulting climatic impacts differ significantly from those associated with El Niño. According to the discussion, La Niña can contribute to flooding in Australia while intensifying drought conditions in other parts of the world.

Global temperatures remained near record levels even during the recent La Niña phase.

The world recently experienced an unusually long La Niña episode lasting around three years, from 2020 to 2022. Despite this cooling influence, global temperatures remained close to the record levels observed during the strong El Niño year of 2016.

This provides important context for understanding the temperature records observed in 2023.

Once climate conditions transitioned from La Niña into El Niño, global temperatures rose decisively to new highs. According to the transcript, this outcome was not unexpected. Long-term warming trends combined with El Niño's warming effect created favourable conditions for record-breaking temperatures.

The observation that temperatures remained elevated even during a cooling phase illustrates the strength of the underlying warming trend affecting the climate system.

Can Scientists Predict El Niño Before It Happens?

(Starts: 00:22:19)

Scientists cannot currently predict El Niño years in advance with high confidence, but they can identify developing events several months before their full effects emerge.

A key part of this forecasting capability comes from the TAO/TRITON moored buoy network across the tropical Pacific Ocean. These instruments continuously monitor ocean conditions and transmit information via satellite.

One important advantage of this monitoring system is that the development of El Niño begins beneath the ocean surface. The shift of warm water can be detected at depth before clear temperature changes appear at the surface. By tracking these subsurface signals, scientists gain valuable lead time before major climate impacts become widespread.

Subsurface ocean observations provide an important early-warning system for developing El Niño events.

This early-warning capability has practical benefits. Governments, communities and industries can use forecasts to support planning for water resources, agriculture and fisheries management. Regions vulnerable to droughts, floods or ecosystem disruptions can prepare for changing conditions months in advance.

As ocean observation systems continue to improve, scientists are gaining a clearer understanding of how large-scale climate phenomena influence both the ocean and society.