We rarely think about how essential and reliable electricity grids are until they fail.

Now, millions of people across Spain, Portugal and parts of France are likely thinking of little else.

While local power cuts are fairly common, what’s happened across the Iberian peninsula is something far more extreme.

Much of Spain and Portugal’s electricity transmission system collapsed in seconds including in major cities Lisbon, Madrid, Barcelona and Seville.

Blackouts latest: ‘Rare atmospheric phenomenon’ behind outages

It’s likely the outage will surpass Europe’s largest blackout to date when 56 million people in Italy and Switzerland lost power for up to 12 hours in 2023.

The cause of the outage is unclear. Portugal’s grid operator has blamed a “rare atmospheric phenomenon” that caused “anomalous oscillations” in high voltage power lines in Spain.

Spain’s grid operator has yet to respond to that or provide an update on the cause. But it’s unlikely whatever caused the outage was a single, localised event.

A major power line going down can cause a large outage – as it did in 2021, when an interconnector between France and Spain failed leaving a million people without power for a few hours.

But it’s unlikely to cause a system-wide failure of the kind we’re seeing now.

However, when things do start to fail on a power grid, they can cascade uncontrollably.

Keeping a grid running is a constant and highly complex balancing act.

Spain’s mains AC electricity supply grid, like ours in the UK, runs at 50Hz. That frequency is based on the speed at which generating hardware such as gas and nuclear turbines spin.

If there are sudden fluctuations in power supply or demand – a power station failing or a high voltage power line going down, for example – the frequency of AC power in the transmission lines changes and circuit breakers trip to protect either the transmission network, or power plant hardware from burning out.

To prevent such failures, grid engineers constantly measure and forecast supply and demand to keep the grid balanced.

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To protect the system in emergencies, they occasionally have to “shed load” by cutting power to parts of the grid – the reason we’ve all experienced the occasional short-lived power cut.

But if balance is lost, a grid can fail in a domino effect with sections of the grid tripping, then power plants shutting down to protect themselves from the drop in demand, one after another.

The challenge now, and it’s a nightmare for Spain and Portugal’s power engineers, is to gradually restore the grid section by section while maintaining the balance of supply and demand.

Act too fast, and the grid can trip again. Take too long and some power plants or substations might struggle to restart – especially if they rely on battery power to do so.

While some regions of Spain have already had power restored, and Portugal says its power will be back to normal within hours, it could take much longer for the system to be fully restored.

A Palestinian diplomat has told the United Nations’ top court that Israel is “starving, killing and displacing” civilians and targeting aid workers in Gaza.

Israel denies deliberately targeting civilians and aid staff and did not attend the hearing at the International Court of Justice (ICJ) on Monday.

At The Hague, Palestinian ambassador to the Netherlands, Ammar Hijazi, accused Israel of breaching international law in the occupied territories.

He said: “Israel is starving, killing and displacing Palestinians while also targeting and blocking humanitarian organisations trying to save their lives.”

The hearings are focused on a request last year from the UN General Assembly, which asked the court to weigh in on Israel’s legal responsibilities after the country blocked the United Nations Relief and Works Agency (UNRWA) for Palestine refugees from operating on its territory.

In a resolution sponsored by Norway, the General Assembly requested an advisory opinion, a non-binding but legally important decision from the court, on Israel’s obligations in the occupied territories to “ensure and facilitate the unhindered provision of urgently needed supplies essential to the survival of the Palestinian civilian population”.

While Israel was not in court, foreign minister Gideon Saar told a news conference in Jerusalem: “I accuse UNRWA, I accuse the UN, I accuse the secretary-general and I accuse all those that weaponised international law and its institutions in order to deprive the most attacked country in the world, Israel, of its most basic right to defend itself.”

Forty states and four international organisations are scheduled to participate in the ICJ hearings, with it likely taking months for the court to rule.

The hearings come amid the near collapse of the humanitarian aid system in Gaza.

Israel has blocked the entry of food, fuel, medicine and other humanitarian supplies since 2 March.

The World Food Programme said last week its food stocks in the Gaza Strip had run out.

Israel also renewed its bombardment on 18 March, breaking a ceasefire, and seized large parts of the territory, claiming it aims to push Hamas to release more hostages.

Overnight into Monday, at least 27 Palestinians were killed in Israeli strikes, according to local health officials.

An air strike hit a home in Beit Lahia, killing 10 people, including a Palestinian prisoner, Abdel-Fattah Abu Mahadi, who had been released as part of the ceasefire.

His wife, two of their children and a grandchild were also killed, according to Indonesia Hospital which received the bodies.

Another strike hit a home in Gaza City, killing seven people, according to the Gaza Health Ministry’s emergency service.

And late on Sunday, a strike hit a home in the southern city of Khan Younis, killing at least 10 people, including five siblings as young as four-years-old, according to the health ministry.

Two other children were killed along with their parents, according to Nasser Hospital which received the bodies.

There was no immediate comment from the Israeli military.

Israel claims it makes every effort to avoid harming civilians and blames Hamas for their deaths because the militants operate in densely populated areas.

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Israel’s ban on UNRWA came into effect in January.

The organisation has faced increased criticism from Prime Minister Benjamin Netanyahu and his far-right allies, who claim the group is deeply infiltrated by Hamas, which UNRWA refutes.

Amir Weissbrod, a foreign ministry official, presented Israel’s case against UNRWA on Monday.

He accused it of failing to act before the war against evidence that Hamas had used its facilities, including by digging tunnels underneath them.

The official said UNRWA employed 1,400 Palestinians with militant ties.

Israel claims some of those employees also took part in Hamas’ attacks on 7 October 2023, with at least three of those employees still allegedly working for the UN.

The presentation included videos, documents and pictures of the alleged employees.

The 7 October 2023 attack in southern Israel killed around 1,200 people and prompted the ongoing Israeli offensive in Gaza – which the territory’s health ministry says has killed more than 52,000 people.

UNRWA said it fired nine staffers after an internal UN investigation concluded that they could have been involved, although the evidence was not authenticated and corroborated.

The ban does not apply directly to Gaza, but UNRWA is prohibited from operating inside Israel which affects the agency’s ability to function.

Israeli officials claim they are looking for alternative ways to deliver aid to Gaza that would cut out the UN.

The conclave to elect Pope Francis’s successor will begin on 7 May, the Vatican has announced.

Some 135 cardinal electors – those under the age of 80 – will take part and vote for the new pontiff.

The rituals of the event, held in the Sistine Chapel, are elaborate and date back centuries. So how does the process work?

When Pope Francis died, the Catholic Church entered a period known as “sede vacante”, meaning “empty seat”.

His ring and seal – used to dispatch papal documents – were broken to prevent anyone else from using them.

Cardinal Kevin Farrell – the Camerlengo, or chamberlain, who announced Francis’s death – became the interim chief of the Catholic Church.

The conclave

Cardinals travel to Rome from all over the world and stay until a new pope is chosen.

Of the 252 current ones, there are 135 cardinal electors: 53 from Europe; 23 from Asia; 20 from North America; 18 from Africa; 17 from South America; and four from Oceania.

Italy has the most cardinals who can vote, with 17, while the US has 10 and Brazil has seven. The UK has three.

Once the conclave begins, the cardinals will not emerge from the Vatican until a new pope has been chosen. The word “conclave” comes from Latin, meaning “with key” – a reference to the isolation in which the cardinals are kept.

While holding voting sessions in the Sistine Chapel, they sleep in the Casa Santa Marta – a guesthouse inside the Vatican’s grounds.

The longest conclave lasted almost three years, between 1268 and 1271. Several have lasted only one day. The one which elected Pope John Paul in 1978 lasted less than three days. Cardinals chose Pope Francis in around two days.

While the conclave is ongoing, cardinals are unable to communicate with the outside world. No telephones, internet use or newspapers are allowed.

Except for the first day, when only one ballot is held, the cardinals hold two daily votes until one candidate has a majority of two-thirds plus one. They are sworn to secrecy about the voting.

White smoke?

So how do we know if a decision has been reached? Yes, this is the black smoke, white smoke part.

If the cardinals have not reached a majority, the cards and the tally sheets are placed in a stove and burned with an additive to produce black smoke, showing the outside world that a pope has not yet been chosen.

Watching for the tell-tale smoke arising from the top of the Sistine Chapel is a tradition, with Catholics crowding into St Peter’s Square for the spectacle.

If no result has been reached after three days, the sessions are suspended for a day to allow for prayer and discussion. More ballots are held until a two-thirds majority is reached.

When enough cardinals have agreed on a candidate, he is asked if he accepts the papacy and by which name he wishes to be known.

The ballots are burned as before, but with an additive to produce white smoke.

New pope proclaimed

The new pope then dons his new papal vestments – tailors keep large, medium and small sizes ready – and sits on a throne in the Sistine Chapel to receive the other cardinals who file up to pay homage and swear obedience to the church’s new leader.

The senior cardinal deacon then steps out on to the central balcony of St Peter’s Basilica overlooking the square and announces in Latin: “Annuntio vobis gaudium magnum. Habemus Papam” (I announce to you a great joy. We have a pope) and reveals the cardinal’s name and the name he has chosen.

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The new pope then appears on the balcony to deliver his first public pontifical greeting and bless the crowds in St Peter’s Square.

A few days later, he celebrates a mass that marks the beginning of his papal ministry.