How Emissions Decline in the Real World

One of the first questions anyone seeking to understand global warming should ask is this: how do emissions decline in the real world?

The short answer is that they mostly don't. As nations develop, emissions go up. The one major exception is during economic recessions and depressions, when energy use temporarily declines before continuing its vertiginous climb.

What does decline is the amount of emissions per unit of GDP produced -- what is known as carbon intensity. Breakthrough Institute recently completed an analysis of long-term data from 1971 to 2006, drawn from 26 developed countries to find out what reduces carbon intensity -- i.e., advances "decarbonization" -- most rapidly. The results are striking.

(See today's excellent overview by the Washington Post's Brad Plumer.)

The nation that decarbonized most rapidly in the examined period was Sweden, at a rate of 3.6 percent per year. That's nearing the rate at which global decarbonization would have to occur if we hope to keep atmospheric carbon to 450 parts per million, absent major recessions or depressions. For context, the annual decarb rate since the mid-1860s has been 1.3 percent.

How did Sweden decarbonize at triple the historical average? Mostly by implementing a long-term, state-driven strategy to replace its oil-burning power plants with nuclear and hydroelectric energy after the oil price shocks of the 1970s. A similar story can be told of France, which unlike Germany had no indigenous coal reserves and steadily scaled up nuclear to displace oil and coal power generation.

Two other nations -- Ireland and the UK -- rapidly decarbonized by reducing energyintensity, the amount of energy required to create a unit of economic output. Energy intensity declines are often misattributed to more energy efficient buildings, appliances, and vehicles. In the case of many countries, including the UK and the US during this period, the decline in energy intensity was mostly due to the offshoring of heavy industries -- in other words, shifting major sources of carbon emissions to other countries.

This historical trajectory makes intuitive sense. Nations transition to new energy sources when they become cheap, widely available, and better than the incumbents.

This pattern has come true in a big way in the United States recently, where against most predictions emissions have started a long-term decline. Awash in natural gas from the shale revolution, old coal plants are coming off-line for cheaper, cleaner gas.

The implication for anyone concerned about climate policy -- that rapid global decarbonization requires making clean energy alternatives cheaper, scalable, and more available -- should be obvious.

-- Michael Shellenberger and Ted Nordhaus

Photo credit: Flickr user swamysk