In the Democratic Republic of Congo, the world's poorest country, life expectancy is 49.

In Scotland in 1850, at the smoggy, unregulated height of the industrial revolution, life expectancy was 42. For rough sleepers living on the streets of Scotland at present, life expectancy is just 39.

Thirty-nine. That chilling figure cuts through political rhetoric about a welfare system that supposedly targets help at those who need it most. It exposes the extent to which even now, in one of the world's wealthiest countries, poverty, unexpected life events and bad luck are enough to condemn the individual to destitution and an early grave. Has so little changed in 200 years? It is quite simply shameful.

Although personal circumstances typically play a part in leading people to sleep rough, no-one wants to spend the night huddled in filthy blankets on a damp cardboard box. No-one wants to cower in a leaky derelict caravan full of cobwebs and draughts. No-one wants to have to live off charitable support.

The reason people do, in a country like Scotland that supposedly offers the safety net of a welfare state, is that human lives are often full of challenge and pain and chaos. For a teenager who has been repeatedly abused, climbing out of the window into a cold, rain-whipped night with nowhere to go can seem safer than the alternative.

A man who has been thrown out of his home after splitting up with his partner may not have the money for a hotel. Men and women living chaotic lifestyles because of mental health problems, alcoholism or drug abuse may fail to find the support to which they are entitled. For these reasons, there will always be individuals who find themselves in need of a bed for the night, or several nights, at short notice, but when people's lives are also buffeted by economic and political turbulence, it makes matters worse.

If there is a chronic shortage of affordable social housing, more people will become vulnerable to destitution. Friends and family may tolerate a sofa-surfer for a few days, but if the visitor's promised council flat does not materialise because of housing shortages, they may be ejected on to the street. Add to that a lack of emergency overnight accommodation and a picture emerges of vulnerable individuals in crisis being badly let down.

Earlier this month, the charity Glasgow Homelessness Network revealed that in the six months from April to September this year, 235 of the 391 people who approached Glasgow City Council after finding themselves homeless were turned away. Of those, 140 ended up sleeping rough.

This is in spite of the council having a duty to provide emergency accommodation to those who need it. Cuts and the council tax freeze have played their part in stretching the available resources to breaking point, but Shelter has spoken of a culture of complacency and not just at council level. Single-sex hostels have been closed in Glasgow over the last decade and there has been insufficient provision in their place.

The Scottish Government must now provide funding to boost the provision of accommodation, to end this scandal in which lives are being cut short.