Next month, representatives from nearly 200 countries will meet in Paris to try to reach a universal and binding agreement to tackle global climate change. Two of the biggest obstacles to such a deal have been the fact that emissions of carbon dioxide and other greenhouse gases vary widely from country to country, and that many leaders fear that limiting emissions can hamper economic growth, especially for newly industrialized countries trying to lift people out of poverty.

A measure that links these two notions is Energy intensity – the total energy used by a country per unit of gross domestic product (energy consumption being closely related to carbon emissions). While not without drawbacks and criticisms, energy intensity is useful as a sort of Energy Star rating for an entire economy: all other things being equal, you would probably prefer to use less energy to generate a given amount of economical output.

While energy intensity can be calculated in several ways, for simplicity we use the version adopted by the US Energy Information Administration (EIA): the total energy used by a country in a year (in British thermal units , or Btu) divided by the country’s GDP for that year (in constant 2005 US dollars on a purchasing power parity basis, so the data is comparable across time and across national borders). The resulting figure represents the number of Btu the country used per dollar of GDP.

Between 1993 and 2011, the most recent year for which data is available, global energy intensity fell 18.7%, according to a Pew Research Center analysis of data from nearly 200 countries and territories compiled. by the EIA; most nations (112) reduced their energy intensity during this period.

Many of the countries that have achieved the largest reductions are countries in the former Soviet bloc (such as Azerbaijan, Estonia and Slovakia), which were historically very energy intensive. Although several factors are probably responsible, a major one seems to be the decline of the steel industry and other heavy industries after 1989 and the subsequent closure of many inefficient factories. Conversely, many countries where energy intensity has increased since 1993 are developing economies which are industrializing and / or extending their electricity networks, such as Benin, Laos and Cambodia; To the extent that new power plants use coal, natural gas or other fossil fuels, greater energy intensity means higher carbon emissions.

Most of the countries with the lowest energy intensities in 2011 tend to be poor nations, largely agricultural in Africa. Chad, whose per capita GDP last year was $ 2,082 (according to the World Bank) ranked last out of 199 countries and territories in energy intensity, using less than 195 Btu per dollar of GDP.

But there was one notable exception: Macau, a special administrative region of China, used only about 761 Btu per dollar of GDP but still has one of the highest GDP per capita in the world: $ 133,341. Last year. The secret? Macau’s economy is dominated by casino games and other businesses related to hospitality and tourism, which generate huge amounts of money ($ 44 billion for casinos alone last year) all using relatively little power (despite all those flashing lights and ringing bells).

As for the United States, it is one of the most energy intensive compared to its peers. Among the 34 member states of the Organization for Economic Co-operation and Development, a group of mostly developed economies, the United States had the eighth highest energy intensity in 2011, about 7,328 Btu per dollar of GDP. While this represented a 28.6% drop from 1993, the United States was still in the middle of the OECD pack (15th, to be exact) in terms of reduction energy intensity. (Of all the countries and territories measured, the United States ranked 58th in energy intensity.)

Among OECD countries, Iceland, Canada and South Korea are the most energy intensive, while Estonia, Ireland and the United Kingdom are the least energy intensive. Estonia, in fact, has reduced its energy intensity the most of any OECD member country: a drop of 59.8% since 1993, largely due to structural changes in the country’s manufacturing base.

This brings up an important point: energy Efficiency is not the only factor determining the energy of a nation intensity. Structural changes in an economy – the industrialization of an agrarian society, for example, or the shift from the manufacturing sector of a developed country to energy-intensive industries such as steel and chemicals – can increase or decrease l energy intensity. The same goes for changes in people’s behavior, such as moving to warmer or colder areas or choosing apartments over single-family homes, as well as demographic changes (women with fewer children, many generations living under the same roof).

By far the most energy-intensive place on the planet came as a surprise: the US Virgin Islands, which uses over 60,000 Btu per dollar of GDP, more than eight times the rate of the continental United States. high ranking, according to an EIA analysis: the islands use large quantities of imported oil to supply the desalination plants that supply their drinking water; many small simple cycle generators are used to supply electricity; and there are “operational constraints and power losses on isolated island power grids”.