Jean-Paul closed the front door. It was good to be home after a cold day on the PyreneanThe Pyrenees are a range of mountains dividing Spain from France. farm. He would turn up the heating, put his wet clothes on the radiator and stretch out his feet in front of the fire. But then he remembered: this was an ultra-modern house. There was no heating, no radiator, no fire.

Sitting by the fire is so relaxing that it has been found to lower blood pressure. Psychologists attribute this to the Stone AgeA prehistoric age in which stones were used as tools. It ended around 4,000BC, when metal began to be used instead., when our ancestors gathered round fires.

Warmth is essential to human survival, but is now endangering it. Using fossil fuels to heat houses is a major cause of global warming.

In the UK, around 15% of greenhouse gases stem from domestic use; in France, the figure is 20%. In Australia, with its warmer climate, households consume 10% of the country's energy.

Various schemes for reducing these figures have been suggested. One is the replacement of gas boilers by heat pumps, which extract warmth from the air, ground or water. In the USA, it has been estimated that replacing gas by heat pumps would reduce CO2 emissions by more than 75%.

But heat pumps cost more than gas boilers: between £6,000 and £18,000. Making them work efficiently demands a high degree of insulation. Although the British government has announced subsidies of £5,000 for switching, households still face a hefty bill.

For some, the answer lies not in making old houses more energy-efficient, but in building new ones that require little or no energy to heat. One particularly exciting idea is the Passive HouseThe original German name is very similar: Passivhaus.. Developed by a German and a Swedish academicWolfgang Feist and Bo Adamson first came up with the idea in 1988., it makes as much use as possible of sunshine, shade and outside air to maintain a comfortable temperature.

Passive Houses have what experts call "superinsulation". While ordinary houses possess weak spotsThese are referred to as "thermal bridging". which allow heat to escape, such as draughty windows, the new design aims to create an airtight "envelope".

This means that very little heat can escape, so the house can be warmed by the body heat of the people inside, and the heat produced by electrical appliances.

Passive Houses also have a heat-recovery ventilator (HRV) to take out stale air and bring in fresh. This extracts heat from the air going out and uses it to warm the air coming in.  

As for keeping cool in summer, a system of blinds and shutters is used to control the sunlight.

Yes. Doing so would have a huge effect on lowering carbon emissions. Passive Houses are clearly the way forward, so every new building should follow their principles. In the meantime, we can put on warmer clothes when the temperature drops: it is a small sacrifice worth making.

No. Most people simply do not have the money to buy state-of-the-art houses. They will have to go on living in old houses. Putting on another jumper will not save old people from dying of hypothermia. In any case, fires and heating provide psychological comfort.