Portugal is experiencing an unprecedented May heatwave, with temperatures soaring above 40°C in several regions, breaking national records for the month. The extreme event has prompted the UK’s Met Office to issue an urgent climate warning, highlighting the accelerating trend of early-season heat extremes that scientists have long predicted as a direct consequence of anthropogenic global warming.
Data from the Portuguese Institute of the Sea and the Atmosphere show that on Tuesday afternoon, the town of Alvega in the central Santarém district recorded 41.3°C, shattering the previous May record of 40.5°C set in 2015. The heatwave has triggered red alerts across large swathes of the country, with authorities advising residents to stay indoors during peak hours and to remain hydrated. Local emergency services have reported a surge in heat-related incidents, particularly among the elderly and those with pre-existing conditions.
From a climatological perspective, the heatwave is the result of a persistent ridge of high pressure drawing hot, dry air from North Africa across the Iberian Peninsula. But the magnitude of the anomaly is what demands our attention. The event is occurring during a La Niña year, which typically cools global temperatures, yet the heat in Portugal is roughly 5°C above the long-term average for May. This is consistent with a warming trend that has seen record-breaking heatwaves become more frequent and more intense across Europe over the past decade.
The Met Office’s warning underscores the transnational nature of climate crises. Their new “Extreme Heat Risk” bulletin, issued in collaboration with European agencies, notes that the heatwave could migrate northward, increasing fire risk in France and the UK later this week. The model projections show that a blocking pattern is locking the heat in place, and with soils already dry from a dry spring, the risk of wildfires is acute. In Portugal, more than 500 firefighters have been pre-positioned in high-risk zones, a stark reminder of the 2017 wildfires that killed over a hundred people.
This is not a story of a single weather event; it is a data point in a trajectory. The physics of the atmosphere dictates that a warmer world holds more moisture, but paradoxically, it can also produce more intense drying in regions at the boundaries of high-pressure systems. The jet stream, weakened by a warming Arctic and shrinking temperature differentials between poles and mid-latitudes, is more prone to these “blocking” patterns. That means such heatwaves last longer and cover larger areas.
We are looking at a biosphere under stress. The heatwave is already impacting agriculture, with olive groves and vineyards in the Alentejo region suffering heat stress at a critical flowering stage. The Portuguese government has activated a drought contingency plan for the Algarve, where reservoir levels are already at 40% of capacity. This is the physical reality of a planet that has warmed by 1.2°C since pre-industrial times. Each tenth of a degree adds risk.
The question now is whether this event will catalyse a more aggressive energy transition. Portugal has made commendable strides in renewable energy, sourcing over 60% of its electricity from wind, solar, and hydro. But heatwaves expose the vulnerability of the system: reduced river flow for hydro and lower efficiency for solar panels at high temperatures. The solution is not just more renewables; it is a fundamental redesign of our grids and a dramatic reduction in fossil fuel consumption.
As I write this, the temperature in Lisbon is 39°C. The streets are empty. The air shimmers. This is not a future scenario. This is now. The data are clear. The time for calm urgency is past; we are in the phase of urgent action.
