As western Europe swelters under an unprecedented heatwave, temperature records are being shattered from Lisbon to London. The British grid operator, National Grid ESO, has issued a rare capacity market notice, signalling an imminent surge in electricity demand as air conditioning use spikes. This is not a crisis of supply but a stark illustration of the physical reality of a warming planet.
In Paris, the mercury hit 42.6°C on Tuesday, eclipsing the previous record of 40.4°C set in July 2019. London reached 40.2°C, the first time the UK has recorded temperatures above 40°C. These are not anomalies but part of a clear trend: the European heatwave season is now arriving earlier and with greater intensity. The Copernicus Climate Change Service confirms that June 2024 was the hottest June on record globally, with western Europe experiencing temperatures 2.5°C above the 1991-2020 average.
National Grid ESO’s notice, issued at 13:00 BST, requests that power generators postpone maintenance and bring additional capacity online. The grid’s capacity margin a measure of spare supply is expected to fall below 1.9 GW, or 5% of total demand, during the peak hours of 16:00-19:00. For context, a margin below 2% triggers a capacity market notice, allowing the system operator to call on reserve units. This is a prudent measure, not a blackout warning, but it underscores how the energy system is being tested by climate extremes.
The physics of this situation is straightforward. A warmer atmosphere holds more moisture, but it also increases the frequency and intensity of heat domes: stationary high-pressure systems that trap heat. The jet stream, weakened by a warming Arctic, becomes more meandering, allowing these heat domes to persist. This is the same mechanism that brought the 2021 Pacific Northwest heatwave, which killed hundreds. The difference now is that infrastructure in temperate climates, designed for mild summers, is inadequate for these extremes.
In the UK, less than 5% of homes have air conditioning. During the 2003 European heatwave, which caused 70,000 excess deaths, the UK saw a 30% increase in electricity demand as people turned to fans and portable units. Today, with higher baseline temperatures and a population more reliant on electronics, the strain is greater. Meanwhile, renewable generation is constrained: wind speeds are low under high pressure, and solar output, while high during the day, is intermittent. Gas-fired power plants, many of which are ageing or mothballed, must fill the gap.
This event is a microcosm of the broader energy transition challenge. The UK has made significant strides in decarbonising its grid: in 2023, renewables provided 47% of electricity. But the transition must account for the fact that a changing climate will increase demand volatility. The solution is twofold: accelerate deployment of grid-scale storage to capture excess renewable energy, and adapt building codes to reduce cooling demand. Passive cooling techniques, such as reflective roofing and natural ventilation, can cut energy use by up to 30%.
Public health officials are also on alert. High night-time temperatures, often exceeding 25°C, prevent the body from recovering, leading to heat stress and increased mortality. In London, the Ultra Low Emission Zone (ULEZ) is temporarily suspended to encourage use of public transport, but many of the city’s Tube cars lack air conditioning, creating dangerously hot conditions for commuters.
We are now in a territory where the physical world is outpacing our preparedness. The coming decades will see more record-breaking events, each one a reminder that climate change is not a future hypothetical but a present fact. The calm urgency of this moment demands that we view heatwaves not as weather events but as system failures that expose our vulnerabilities in energy, health, and infrastructure. The grid operator’s alert is a canary in the coal mine: we must listen.
