A Foxconn factory, where all your outsourced carbon needs are met. (Bobby Yip/Reuters)

In the past three decades, most of the world’s wealthiest countries appear to have relied heavily on that last route. At least, that’s one way to read an interesting new analysis from the Breakthrough Institute, which looks at how developed nations have “decarbonized” between 1971 and 2006. You can see the full table below, but here’s the nickel version. A handful of countries, including Sweden, France and Belgium, have managed to become more carbon-efficient largely by using cleaner forms of power. The rest, however, seem to have largely decarbonized through the process of transforming into service economies and shifting their industrial and agricultural needs abroad.

The full Breakthrough report is here. I’ve truncated their chart a bit to show the key elements. In the first column is the rate of “decarbonization,” which shows how much a country is reducing carbon dioxide emissions per unit of economic activity. This is a key metric. If the world wants to avoid a dangerous 2°C or more rise in world temperatures, then all of the world’s nations need to “decarbonize” at a rate of at least 4 percent a year from now until 2050, according to the International Energy Agency.

As you can see from the chart, that would be an unprecedented task. Since 1971, the world’s nations have naturally become more efficient over time, but no wealthy country has decarbonized at a rate of 4 percent a year. The closest has been Sweden, which has managed a 3.6 percent decarbonization rate. (Granted, many of these nations have only recently tried seriously to cap carbon emissions, so faster rates may be possible in the future.)

What’s more, there’s a real divide between how countries have actually weaned themselves off carbon. The second column of numbers in the chart above shows how much “decarbonization” a country got by reducing its energy intensity. Some of that comes from becoming more efficient. But a lot appears to come from sloughing off the dirtiest sectors, like farming and manufacturing, abroad.

In the past 30 years, Ireland, for instance, has transformed itself from an agricultural backwater to a thriving service economy. That’s been good for Ireland’s carbon intensity: Farming, after all, produces a lot of emissions — all those tractors and belching cows — and Ireland’s been doing less of it. But the Irish people haven’t stopped eating food. They’ve just imported more from other countries. So, even as Ireland’s coal and oil use has soared (pdf), the country has looked like it’s decarbonizing. But that’s a bit of a cheat.

The same goes for Britain and the United States, which have become less carbon-intensive in part because manufacturing has become less important and imports have surged. (In the United States, manufacturing’s share of the economy has fallen 45 percent since 1971 and imports’ share has increased 200 percent.) Essentially, these countries are outsourcing their carbon pollution. A 2011 study in the Proceedings of the National Academies of Science found that these “outsourced emissions” essentially cancel out any progress made under the Kyoto Protocol.

The third column in the Breakthrough chart above, meanwhile, looks at how much decarbonization occurred because a country actually shifted to cleaner energy sources. Countries bolded in this third column have managed to become more carbon-efficient largely without cheating. France, for instance, achieved much of its decarbonization since 1971 by making a big push on nuclear power. Likewise, Sweden has been using less oil over the past four decades, while relying more on nuclear and geothermal and biofuels. Here’s a chart for France, with the nuclear surge in yellow:

Now, the Breakthrough report isn’t an advertisement for nuclear power. What it shows is that a global effort to mitigate climate change would require a sharp break with the past. Not only would countries have to decarbonize at a much faster rate than they’ve managed to do over the past 40 years, but they’ll need to do it by relying more heavily on low-carbon forms of energy, as France and Sweden have done. They can’t keep simply outsourcing factories and farms off to countries like Brazil, China and India.

After all, if a country like Britain is pushing all its manufacturing to China, then the Brits may look more virtuous on paper, but those outsourced carbon emissions are still heating the planet.