A study by an MIT (Massachusetts Institute of Technology) class has estimated that anyone who lives in the US contributes more than twice as much greenhouse gas to the atmosphere as the global average.
The class studied the carbon emissions of Americans in a wide variety of lifestyles and compared them to those of other nations. They conducted detailed interviews or made detailed estimates of the energy usage of 18 lifestyles.
The energy impact for the rich was estimated from published sources, while all the others were based on direct interviews.
The team found out that in the United States, even people with the lowest energy usage account for, on average, more than double the global per-capita carbon emission.
The average annual carbon dioxide emissions per person, they found, was 20 metric tons, compared to a world average of four tons.
It was also determined that those emissions rise steeply from that minimum as people's income increases.
"Regardless of income, there is a certain floor below which the individual carbon footprint of a person in the US will not drop," said Timothy Gutowski, professor of mechanical engineering, MIT.
While it may seem surprising that even people whose lifestyles don't appear extravagant - are responsible for significant greenhouse gas emissions, one major factor is the array of government services that are available to everyone in the United States.
These basic services - including police, roads, libraries, the court system and the military - were allocated equally to everyone in the country in this study.
Other services that are more specific, such as education or Medicare, were allocated only to those who actually make use of them.
In general, spending money on travel or on goods that have substantial energy costs in their manufacture and delivery adds to a person's carbon footprint, while expenditures on locally based labor-intensive services leads to a smaller footprint.
The students looked at the factors within each person's control that might lead to a reduction in carbon output.
They found that achieving significant reductions for the most part required drastic changes that would likely be unacceptable to most people.
As a result, they said, "This all suggests to us very significant limits to voluntary actions to reduce impacts, both at a personal level and at a national level."