Blackouts Without Borders: Lessons from the Iberian Power Failure

A major blackout in the Iberian Peninsula highlights a growing global issue: our power grids are more vulnerable than ever. The recent power failure offers important lessons about the resilience of modern energy systems and how better planning could reduce the risk of future large-scale outages.

Power Is Back On – But the Warning Signs Remain

On Monday, 28 April 2025, millions of people across the Iberian Peninsula (Spain, Portugal and southern France) were plunged into unexpected darkness as a major blackout swept through the region. The disruption brought everyday life to a standstill – traffic lights went dead, ATMs stopped working, public transport services were halted, and mobile networks dropped out.

As night fell, countless people were left eating dinner by candlelight, while others were trapped in lifts and stranded on immobilised trains. This was potentially dangerous, leaving people without communication or access to money to get home or reach a place of safety.

How Most Blackouts Occur

Large-scale power blackouts can be triggered by various factors, often acting together.

Earthquakes, for example, can lead to widespread outages. Weather-related events are a leading cause of power failures globally, accounting for 83% of blackouts in the USA between 2000 and 2021.

High winds can bring down power lines or cause them to vibrate, potentially resulting in short circuits if the lines touch. Lightning strikes can damage critical components such as transformers and generators. Bushfires can destroy vital infrastructure, while conversely, sparks from electrical substations can start wildfires, as seen in the Los Angeles wildfires in early 2025.

In some cases, insufficient grid redundancy or power demand exceeding supply – such as during heatwaves when air conditioning units draw excessive power – can lead to system failures. Equipment malfunctions can destabilise the grid when parts fall out of synchronisation. Human error and cyberattacks on control systems can further disrupt electricity networks.

Geomagnetic Storms – Blackouts Caused by the Sun

There are well-documented blackouts where the cause is extraterrestrial.

The Sun not only releases a solar wind (a continuous flow of protons and electrons) but occasionally produces solar flares. These are often followed by a coronal mass ejection (CME), where a cloud of up to one billion tons of charged particles is expelled into the interplanetary medium (see Image 2).

Image 2 A coronal mass ejection in April 2023

On 6 March 1989, an intense solar flare occurred, followed by a CME on 9 March and a geomagnetic storm four days later. In just 92 seconds, the storm knocked out the Hydro-Québec power grid, causing a widespread blackout that left over six million people in North America without electricity for nine hours (see Image 3).

Image 3 Simulation of an extreme geomagnetic storm showing probable collapse zones across the US power grid

So, What Causes Geomagnetic Storms?

As a CME is a moving cloud of charged particles, it carries a magnetic field that interacts with Earth’s magnetic field, causing it to oscillate. These fluctuations induce voltages, which in turn generate geomagnetically induced currents (GICs) on Earth’s surface. These currents follow paths of least resistance, such as overhead power lines and the ground.

In Quebec, much of the region sits on rock with high electrical resistance, which led the current to travel through the 735 kV power lines. This vulnerability is one reason why North America is particularly susceptible to solar storms. In extreme cases, GICs can overheat and damage heavy-duty transformers, which can take over a year to replace. Without spare transformers, this could significantly disrupt the long-term supply of electricity.

A Mysterious Cause of the Iberian Blackout?

Spanish Prime Minister Pedro Sánchez has stated that the exact reason behind the Iberian blackout in April 2025 is still under investigation.

Early reports from Portugal’s national grid operator, REN, stated that “due to extreme temperature variations in the interior of Spain, there were anomalous oscillations in the very high-voltage lines (400 kV), a phenomenon known as ‘induced atmospheric vibration’.” These oscillations reportedly caused synchronisation failures between electrical systems, leading to successive disturbances across the interconnected European network.

But what does “induced atmospheric vibration” actually mean? And is it really possible for atmospheric conditions to bring down a modern power grid?

What Are ‘Induced Atmospheric Vibrations’?

While “induced atmospheric vibration” is not a recognised meteorological term, differences in pressure can cause atmospheric oscillations known as gravity waves or acoustic-gravity waves.

Oscillations in the atmosphere are common. They can occur when one layer of the atmosphere moves at a different speed or direction from the one beneath it, or when air passes over an obstacle such as a mountain, causing downwind oscillations. As air rises it cools, moisture condenses to form clouds, and when it sinks again these clouds evaporate. The oscillating air can therefore form clouds arranged in neat lines.

However, it is unlikely that “induced atmospheric vibration” means that the atmosphere physically shakes the power lines like wind might. Instead, it is more likely that changes in air conditions (temperature, humidity and pressure) altered the electrical behaviour around high-voltage lines – particularly through a phenomenon known as corona discharge.

When temperature increases or humidity decreases, the air around high-voltage power lines can become ionised. This occurs when the electric field strength surrounding a conductor becomes strong enough to ionise the surrounding air. When the voltage gradient at the surface of the conductor exceeds the air’s dielectric strength, ionisation leads to a phenomenon known as corona discharge.

During corona discharge, the air around conductors becomes partially conductive, allowing electricity to leak out in the form of a faint bluish glow (sometimes known as St. Elmo’s fire) and a hissing sound (see Images 4 and 5). You can think of it as very weak lightning. This does not happen with everyday electricity, only around high-voltage (400 kV) power lines.

Image 4 Long-exposure photograph of corona discharge on an insulator string of a 500 kV overhead line

Image 5 Corona discharges on the 380 kV overhead power line over the Albula Pass (Switzerland)

These discharges can occur in bursts or at specific frequencies, which could cause changes in voltage across the wires and interfere with current flow.

The Bigger Problem: Grid Vulnerability

When we use electricity, it is not simply a case of “turn it on and it works”. National grids are complex systems that must keep voltage and frequency within tight limits.

One challenge is reactance – where electrical energy is slowed or temporarily stored by components such as coils and capacitors. This can waste energy or destabilise the system.

Professor David Brayshaw, Professor of Climate Science and Energy Meteorology at the University of Reading, explains:

“Power systems are networks. They must balance supply and demand almost instantaneously, and generators need to stay precisely in sync (AC 50 Hz). If something on the network – a generator, a power line, or even a large electricity user – suddenly disappears, it creates a supply-demand imbalance, and the system frequency starts to shift. If that shift becomes too large, other components can trip offline, creating a snowball effect that worsens the imbalance and can trigger a major blackout – sometimes within seconds. If this event was indeed driven by atmospheric conditions, it underlines the urgent need for much deeper investigation into climate risks for power.”

Professor Jianzhong Wu, Professor of Multi-Vector Energy Systems at Cardiff University, adds:

“Networks are not designed to be completely blackout-free because achieving such a level of reliability would require investment far beyond what is economically feasible… each blackout has had its own cause.”

This is sometimes referred to as the Swiss cheese model of system failure – where each slice represents a layer of defence (for example engineering safeguards, system monitoring, regulatory oversight or redundancy in supply). Each layer contains weaknesses, represented by the holes. Normally these weaknesses do not align. However, when multiple failures occur simultaneously and the ‘holes’ line up, a pathway opens through the entire system, resulting in large-scale collapse (see Image 6).

Image 6 Swiss cheese model of system failure

While a single problem may not lead to system failure, if several occur simultaneously and align, collapse can occur.

The Solution? Think Local

Satellites offer advanced warning of geomagnetic storms. Analysing images from SOHO (Solar and Heliospheric Observatory) and NASA’s twin STEREO spacecraft generates a 3D model of a CME and predicts its arrival at Earth.

In addition, the ACE spacecraft, located about 1.5 million kilometres upstream of Earth, measures the speed, density and magnetic field strength of CMEs, offering around 30 minutes’ notice for ground teams to disconnect transformers and other vulnerable components.

There is no doubt that scientists and engineers are investigating what happened with the Iberian blackout and will recommend measures to make electricity grids more resilient.

However, another way forward is to shift away from overly centralised systems towards community microgrids – small, decentralised energy networks that can operate independently when needed.

When the main grid fails, microgrids can keep power flowing to homes, businesses and essential services – providing not just electricity, but peace of mind.