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.
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.