Londoners face temperatures soaring to 40C in their homes in the first heatwave of the year that could bring the hottest May day ever.
The capital is due to swelter in increasingly hot temperatures over the Bank Holiday weekend, forecast to reach 33C on Monday.
This would be higher than the UK’s current May temperature record of 32.8C.
It has led to the UK Health Security Agency to upgrade its heat health alert to amber meaning a “rise in deaths” due to the hot weather.
Many areas will also be hotter than Barbados and top European holiday spots including Mykonos, Marbella and Benidorm.
Temperatures tend to rise particularly sharply in London due to the "urban heat island' effect which means it can be 10C hotter than rural areas outside the capital.
Some homes, particularly with glass frontages and only one external wall so there is no through draught, can be particularly vulnerable to overheating.
The UKHSA amber alert for London is running from 2pm on Friday to 5pm on Wednesday. It replaced a yellow amber warning that was already in place.
It stressed that significant impacts are likely across health and social services, including:
- a rise in deaths, particularly among those ages 65 and over or with health conditions. There may also be impacts on younger age groups.
- likely increased demand on all health and social care services
- internal temperatures in care settings (hospitals and care homes) may exceed recommended threshold for clinical risk assessment
- the heat affecting the ability of the workforce to deliver services
- indoor environments overheating increasing the risk to vulnerable people living independently in community and care settings
- issues managing medicines
- staffing issues due to external factors (for example, affecting transport)
- increased demand for power exceeding capacity
Christian Deilmann, managing director at tado° smart heating systems, told the Standard: "Indoor temperatures typically rise progressively over consecutive days of hot weather, as heat gradually builds up inside homes, particularly in densely built urban areas such as London.
“For the first day of warm weather (Friday), previous tado° data suggests some homes could already reach indoor temperatures of around 28C at peak times.
“However, by Bank Holiday Monday, where temperatures are expected to reach highs of 32C in parts of the UK, some homes could see indoor temperatures climbing as high as 38C.”
The predictions were based on an analysis of anonymised temperature data from tado° devices, compared with outdoor temperatures over summer months.
It found that an average outdoor temperature in London, for the day and night, during the summer months of 17.8C could translate into 23.6C on average indoors.
Temperatures could hit 27C in London on Friday in what is expected to be the hottest day of the year so far, following an unusually cool May.
Clouds and thundery showers could hinder Saturday’s heat but if they do not appear then temperatures could exceed Friday’s.
A heatwave in the capital would then be possible by Sunday, according to the Met Office.
Temperatures in workplaces, schools, hospitals, the Tube, trains, buses, as well as homes, could become uncomfortably warm.
The heatwave threshold for London at this time of year is 28C for three consecutive days in the same location.
The Government’s climate change advisers are warning that air conditioning will become increasingly common in England, particularly the South East, as temperatures rise in coming years.
Britain’s Climate Change Committee is also urging the Government to set maximum temperature rules for workplaces and to consider changing the school year so pupils are not forced to sit important national exams in summer heat.
The CCC estimates that investing to protect the UK from climate change will cost around £11 billion a year of public and private money up to 2050.
But the advisers said climate change impacts were already costing up to £60 billion a year in flood damages, crop losses, excess deaths, decreases in productivity, and disruption to transport and health services, with that figure set to rise to as much as £260 billion a year by 2050.
More money needs to be spent on flood defences for London, while building in flood plains should be avoided unless risks can be reduced.
Dr Richard Millar, from the committee, said there was “unequivocal evidence that climate change is making extreme weather here in the UK, such as heatwaves, heavy rainfall, and the conditions for drought, more likely”.
The world has already warmed by 1.4C as a result of human activities such as burning fossil fuels, and on current trajectories will be 2C above pre-industrial levels by 2050, with a “real risk” of hitting 4C heating by 2100 under worst-case scenarios, he added.
Without action to help people adapt, the increasing risk of heatwaves in the 40Cs by mid-century could lead to as many as 10,000 excess deaths a year, according to the committee.
By 2050, heavy rainfall could become more intense, sea levels could rise 20-45cm and peak river flows could nearly double, raising the risk of flooding, it stressed.
