Efficiency or sustainability? Devil's in the details

There are lots of ways to measure how efficient a thing or process is: miles per gallon, GDP per barrel of oil, lumens per watt, etc.

There are also, as Mark Twain (or was it Benjamin Disraeli?) said, “three kinds of lies: lies, damned lies and statistics.”

What does that have to do with efficiency? Quite a bit, depending on the way you measure how efficient our energy use is. That’s because the measures we choose to focus on can sometimes be as misleading as “lies, damned lies and statistics.” Efficiency, for all its positive benefits, does not necessarily mean sustainable … and we need to be careful we don’t conflate one with the other.

One problem with efficiency measures is that they’re “per” metrics — per person, per barrel, per dollar. That means if the absolute number of people, barrels or dollars goes up, so too can consumption, even if the efficiency “per” is improving.

For example, look at US oil efficiency per dollar of gross domestic product. As the chart here shows clearly, that measure has been improving steeply and steadily for more than 30 years. That’s certainly a good thing. But it doesn’t mean the absolute number of barrels of oil the US consumes has declined commensurately. (Although total US consumption has declined slightly over the past several years, with the recession and slow recovery being largely to blame.)

The problem is even more evident in the world’s developing economies. Fast-growing China, for instance, is becoming far more efficient … but it’s still using more energy than ever.

In fact, global energy intensity — measured in tons of oil equivalent per thousands of dollars in GDP — has been on a clear downward trend for around 40 years, as the latest Energy Outlook from BP shows. But total global energy demand? Still projected to rise for the next two decades.

Over the past several decades, cars, electronic devices, home construction, you name it, have all become far more efficient, too. But their drain on global energy supplies continues going up because we keep adding so many more of them.

And then there’s the problem of tying efficiency to GDP in the first place. As many critics of the GDP measure have pointed out, gross domestic product doesn’t mean good gross domestic product. Businesses that are profitable but highly polluting can help boost GDP, as can natural disasters, obesity-promoting junk-food industries and an expanding market for prisons.

For as long as we’ve consumed energy — petroleum in particular — that consumption has been “a key proxy of economic activity.” That means killing the oil-consumption goose while still enjoying the golden egg of a healthy economy will require a whole lot more than simply improving our auto mileage or energy-intensity scores. As David MacKay notes in his book, “Sustainable Energy – without the hot air,” low-carbon is good … but low-carbon does not necessarily mean “sustainable.” We need to make sure we stay focused on the right one.