Researchers say three year study in Cardiff has found there is a potentially untapped source of heat beneath cities across the UK.
They used 61 boreholes to test the temperature of the groundwater. They found, at around ten metres down, there is enough heat to be exploited by a heat pump.
We know the use of ground source heat pumps changes the ground temperature by several degrees Celsius. What we didn't know was by how much.
If everyone in the world consumed natural resources and generated carbon dioxide at the rate we do in Cardiff, we would need three planets to support us and that is not sustainable.