Friday, August 10, 2007

Energy intensity and the challenge that lies ahead

A passage about "energy intensity" in the, er, cheery Thomas Homer-Dixon book The Upside of Down got me thinking more about the historical trend in GHG emissions intensity.

For new readers, a couple months back I showed that the globally-averaged emissions intensity has been decreasing for decades even though the total emissions were increasing. In other words, the economy has been expanding faster than GHG emissions. Therefore, a future emissions target based on the rate of emissions per economic production, as was proposed in Canada, would allow total emissions to increase.

It is instructive to break the long-term trend in global emissions intensity into two component parts: the energy intensity, the energy use per unit of GDP, and the "GHG efficiency" of energy use, the GHG emissions per unit energy production. It is done below using energy data from the
History Database of the Global Environment (similar analysis has been done for the recent past by the IPCC's WG III and by Informetrica for Canada alone).

The graph shows that the emissions per unit energy - the blue line - has been relative stable since the Industrial Revolution. The energy intensity- the green line - mirrors the original emissions intensity curve. It peaked in the 1920s and has been decreasing since.

In other words, the emissions intensity has been falling for the past eighty years because we’ve been producing more stuff with less energy not because we’ve become more efficient, emissions-wise, at producing energy. Over the past three decades, world energy production has actually became less GHG efficient due largely to increased energy use in Asia. Emissions intensity decreased during this time only because, as a planet, we were able to produce more income with less energy.

The graph is useful for articulating the challenge that lies ahead. Since it will take time to rebuild the existing energy production infrastructure ("slow turnover of capital stock"), becoming more energy efficient, producing more stuff with less energy is critical to reducing greenhouse gas emissions in the short-term. That's the green line. But to achieve the long-term emissions reductions (ie. like these proposals) required to avoid dangerous interference with the climate, we'll need to move the blue line. In other words, we'll need to radically change the way be produce, not just use, energy. And, again, with the slow "turnover of capital stock", we need to start planning as soon as possible.


Caspar Henderson said...

My browser won't open the graph, but if I understand your distinction correctly -- energy intensity (the energy use per unit of GDP), and the "GHG efficiency" of energy use (the GHG emissions per unit energy production) -- then it looks to me as if what we are basically talking about the for the latter is the amount of energy used to produce a unit of fuel. Coal (usually) takes more energy to produce than oil or gas so this would account for decline after 1920 or so as oil rapidly grew as part of the main fuel mix. Recently, coal production has greatly increased. A future with (more) Canadian tar sands and/or (not so much efficient PV as advocates believe) would not be a good start. But am I misunderstanding some basic definitions here? Apologies if this is a stupid question.

Simon Donner said...

The graph should now be compatible with all browsers (?)

Simon Donner said...

Here what I'm calling the GHG efficiency of energy is the global GHG emissions divided by the global energy consumption. So Caspar's probably right, in a future with more coal than natural gas or conventional oil, or a future with more oil from tar sands (which has a low "energy return on investment", to use Homer-Dixon's term), the GHG emissions per energy consumed/produced would go up.

Anonymous said...

I'd recommend a quick look at David Strahan's "The Last Oil Shock: A survival guide to the imminent extinction of petroleum man", or take a look at his website:

Peak Oil = 2015 +/- 5 years, according to lots of estimates by knowledgable people. Given that demand continues to go up, and that supply will start going down sometime in next decade, oil price will go up, and natural gas price tends to correlate. OIl/gas are just to useful not to use, so we will.

The main issue will be:

WILL we figure out how to sequester the CO2 from coal plants soon enough? because, if we don't do PV, etc fast enough, there will be incredible pressure to keep building coal plants to keep the lights on.
Jeff Goodell's "Big Coal" is a good book on that topic.