Heat pumps show how hard decarbonisation will be

They hang from the walls of utility rooms, nestle inside kitchen cupboards and hunker down in cellars. Gas and oil boilers and furnaces have been making homes more comfortable for decades. Their adoption during the 20th century brought people central heating and hot baths on demand, and allowed them to stop shovelling coal. But if the goal of decarbonisation is to be met, these boilers must go.Twelve European countries plan to phase fossil fuels out of the heating of buildings, and air-source heat pumps have emerged as the best alternative. These extract ambient heat from the outside air, even when it is below freezing, and concentrate it to warm inside spaces. Heat pumps are far more efficient than boilers, in terms of the amount of energy used per unit of heat generated. Lately, however, they have become a symbol of the obstacles that await as countries try to decarbonise. Until recently, green policies had seldom required private citizens to roll up their sleeves and make big, disruptive changes to their lives. Now they are starting to, and many people do not like it.