It is common to hear people talk about the efficiency of this-or-that system. Being "efficient" sounds like an unequivocal good, but the question that must be asked is "efficient at what?"
To illustrate this, let's consider "A tale of two heaters" in an average Australian living room.
Heater A is a split system heat-pump. It draws 2 kW of electricity, and outputs 8 kW of heat (it does this by pumping heat from outside the house to the inside of the house). For every 1 kWh of electricity it uses, it puts 4 kWh of hot air into the living room, and has a coefficient-of-performance (COP) of 4.
Heater B is a far-infrared panel (FIR). It is a resistive heater that emits infrared light, and needs to be directed to the occupant to be effective. As a resistive heater, it outputs 1 kWh of directional heat for each 1 kWh of electricity it consumes -- its COP is 1. Let's say it draws 1 kW.
Many people would say that Heater A is "more efficient", and there is some justification for this: for a given electricity consumption, heater A puts more heat into the room than does heater B.
However, because Heater B is targeting its heat directly at the occupant, it doesn't need to put so much heat into the room for the occupant to feel warm. Hence, one can argue that the amount of energy required to provide the service (making the occupant feel warm) is less and hence the FIR is more efficient because it uses less energy to make the person feel warm.
Hopefully, this example shows that when talking about efficiency, it is very important to be clear about exactly what we are doing efficiently.
Deep problems with efficiency
But the problem goes deeper than this.
In the 19th century, Britain was worried about running out of coal. At the time, coal was the fuel that drove the factories and war machine that made Britain the world's preeminent power. Some people thought that, as the machines became more efficient, coal consumption would be reduced.
William Jevons argued the opposite -- that an ability to use the resource more efficiently would actually drive increased demand in the resource. He noted that coal consumption rapidly increased after James Watt's more-efficient steam engine, because Watt's new engine made the exploitation of coal much more profitable.
This has become known as Jevon's Paradox, and the Wikipedia article contains much more detail.
We face the same phenomenon today -- improved technology that allows people to climate-control their houses more cheaply has meant that people perform more climate control. Whereas in the early-to-mid 20th century, an internal house temperature of 13 degrees was considered acceptable, it no longer is. Some people even heat their houses to 24 degrees.
Even if you don't do this, consider what you do with the money you save by spending less on fuel -- if you use that money to take more air travel, or to buy more manufactured goods, then you are a living demonstration of Jevon's Paradox.
In a society where 70% of grid electricity comes from coal, as does probably above 90% of the embodied energy in many manufactured goods (such as PV panels), it is simply not good enough to be "efficient". Efficiency, by itself, will not reduce carbon emissions -- not even in theory.
The only solution is to focus instead on reducing consumption.
