It’s estimated around 150 million people worldwide are homeless – around 2% of the global population.

But the actual number could be much higher, because there are many states of homelessness – and many causes, too.

Too often, people without a permanent home fall off the edge of the recorded world. They don’t appear on official registers, in census declarations or in social security records. This compounds the homelessness problem in two distinct but connected ways: it makes it impossible to say how many people are homeless and it creates further difficulties in trying to come up with solutions.

But a number of innovative approaches to homelessness are creating both short-term and long-term solutions.

The UK capital is one of the world’s most-visited cities – and the red double-decker bus is an iconic, must-see sight. But strict emissions regulations have pushed many of the older buses off the road and into retirement.

Now, a social enterprise called Buses4Homeless is converting some of those decommissioned vehicles into accommodation, classrooms, diners and health centres.

One bus can provide shelter for 16 people, who are also given vocational and life-skills training. Their health and wellbeing are also looked after while they’re under the care of the charity.

Finding work and being able to earn enough money to afford somewhere to live are obviously important for people trying to break out of the cycle of homelessness. Elsewhere in London, coffee is helping do just that.

An organization called Change Please is training homeless people to become baristas and work in its fleet of mobile coffee stores. Founder Cemal Ezel says, “If we can just get a small proportion of coffee drinkers to simply change where they buy their coffee, we could really change the world.”

In Delhi, the charity Aashray Adhikar Abhiyan trained 20 homeless people to repair mobile phones. Almost half of those who completed the course went on to either find work or start their own businesses. The organization plans to run the course again next year.

UK charity Crisis lists the following as some of the common causes of homelessness:

This means there is no one-size-fits-all solution, and the solution one person’s problems might only offer temporary respite for another.

Addressing the symptomatic problems of homelessness can be beneficial, but it won’t automatically fix the root cause of an individual’s circumstances.

For someone struggling with poor mental health or substance abuse, for example, it can be practically impossible to meet the commitments of training and employment.

These people can find themselves outside of possible routes to help, too, with some shelters and hostels not accepting people who have not dealt with their addictions.

The US-based non-profit Community Solutions believes it may have an answer, though.

Across the United States, more than half a million people are homeless. Most of them are sleeping in shelters and transient accommodation.

As Community Solutions says, “No single actor is fully accountable for ending homelessness in a community. Each local agency or programme holds its own small piece of the solution, but no one has their eye on how the pieces fit together.”

Therein lies the explanation for the intractability of homelessness. Operating in isolation from one another, even the most effective and well-intentioned of support services can fail to see the bigger picture.

By connecting all the different agencies and organizations that interact with homeless people, Community Solutions’ president Rosanne Haggerty believes homelessness can be eliminated altogether.

“Imagine a world where homelessness is rare, brief when it happens, and really gets fixed for those people to whom it happens – the first time,” she says.

In Abilene, Texas, they can do more than just imagine. They can see the results. Following the Built for Zero programme championed by Community Solutions, the Abilene authorities set the goal of zero homelessness.

Their first target was the homeless veterans’ community, which has now been completely eradicated by moving everyone into a home of their own.

A similar philosophy has been adopted in the Finnish capital, Helsinki. Rather than offer housing only to people who have taken steps to fix some of their everyday problems, such as substance abuse, the authorities now follow a homes-first approach.

Finland is the only EU country where homelessness is in decline. And it started by scrapping hostels and shelters that had been providing short-term respite for homeless people.

“It was clear to everyone the old system wasn’t working; we needed radical change,” says Juha Kaakinen, who runs an organization called Y-Foundation, which helps deliver supported and affordable housing.

“We decided to make the housing unconditional,” he says. “To say, look, you don’t need to solve your problems before you get a home. Instead, a home should be the secure foundation that makes it easier to solve your problems.”