Portugal has recorded its hottest May day in history, with temperatures soaring to 47.1°C in the central district of Santarém on Tuesday. The extreme heat, driven by a persistent atmospheric blocking pattern over the Iberian Peninsula, has intensified a heatwave that now poses a direct threat to British energy supplies.
The record, verified by the Portuguese Institute of the Sea and Atmosphere (IPMA), surpasses the previous May high of 46.3°C set in 2020. “This is not an anomaly. It is a consistent signal of a warming climate,” said Dr. Helena Vance, Science & Climate Correspondent. “The physics are clear: greenhouse gases trap heat, and the system responds with more frequent and severe extremes.”
The heatwave has exacerbated drought conditions across southern Europe, reducing river flows and straining hydroelectric capacity. Crucially, the heat has also triggered a surge in electricity demand for cooling, while simultaneously reducing the output of thermal power plants due to cooling water shortages.
For Britain, the immediate concern is the vulnerability of its interconnected energy grid. National Grid, the UK’s electricity system operator, has issued a notice warning of reduced interconnector capacity from France and Spain. The IFA interconnector, which supplies up to 2 GW of electricity from France, has been operating at reduced levels due to high water temperatures in the English Channel, limiting cooling efficiency for French nuclear reactors.
“The UK imports about 8% of its electricity, much of it from continental Europe,” Vance explained. “When a heatwave hits the continent, our energy security is directly affected. We are increasingly tied to a system that is stressed by climate extremes.”
Data from the European Network of Transmission System Operators (ENTSO-E) shows that power flows from the Continent to Britain have fallen by 15% over the past week, coinciding with peak demand during an unseasonably warm spell in the UK. Temperatures in parts of southern England have reached 28°C, 6°C above the average for this time of year.
The crisis highlights the interconnected nature of modern energy systems and the cascading risks posed by climate change. Vance noted: “Energy transitions are not just about replacing coal with renewables. They are about building resilience against a climate that is already shifting. Our infrastructure was designed for a world that no longer exists.”
The Met Office has issued a Level 3 heat-health alert for much of England, warning of “significant impacts” on health and infrastructure. Meanwhile, National Grid has activated contingency measures including requesting emergency generation from coal plants and offering payments to large users to reduce demand.
This is the third time this year that the UK has faced grid stress due to extreme weather. In January, a cold snap sent electricity prices to record highs; in April, an early heatwave caused solar generation to peak but also triggered outages in distribution networks.
“Every degree of warming makes these events more likely,” Vance said. “Portugal’s record is a symptom of a global fever. We need to decarbonise urgently, but we also need to adapt. The two are not in opposition; they are part of the same response.”
The heatwave is forecast to persist into early June, with temperatures across Iberia remaining above 40°C. For Britain, the immediate task is to keep the lights on. For the world, the message is stark: the future is already here, and it is hot.
