While turning down your thermostat, taking public transportation, and buying locally grown food could all reduce your household’s carbon emissions, just how effective each of those individual strategies is depends on who you are and where you live, according to researchers at UC Berkeley.

The study, authored by Christopher M. Jones and Danial Kammen of Berkeley’s Renewable and Appropriate Energy Laboratory (RAEL), analyzed thousands of different “types” of typical carbon footprints by looking at households in all 50 states, including six different household sizes and 12 different income brackets.  They used data from the US Labor Department’s Consumer Expenditure Survey.

The results of the analysis are summarized in a new “carbon calculator” that can help people estimate their carbon footprints and identify the areas where lifestyle changes would have the largest impact.  Users can also compare their footprints to similar households in their own area.

“Comparative feedback is an effective way to send signals to individuals,” said Jones. “”If people learn they are doing worse than their peers, that may lead them to reduce.”

In the United States, household consumption accounts for over 80% of total emissions, according to the study. In typical US households, the researchers found that one-third of those emissions come from transportation, a little more than 20% are from household energy use, and about 15 percent are from food.  The rest some from everything else: goods, services, housing construction, waste, and water.

However, when you drill down to specific household types, the numbers change.  For example, while the study found that an upper-income couple in San Francisco with no children has roughly the same emissions as a middle-income family with three children in St Louis, the source of those emissions varies greatly.  For the San Francisco couple, travel by car and air are the biggest chunk, while for the St Louis family, more emissions come from food and electricity.

So, when it comes to making effective changes, the two families would likely have different action plans.

“Our primary message is simple: If you are concerned about reducing your carbon footprint, or the carbon footprint of others through policy, it is important to focus on the actions that lead to the greatest reductions,” said Kammen in a press release.  “Our online tool can help people do just that.”

The new online tool lives at CoolCalifornia.org, which is a partnership of RAEL, Lawrence Berkeley Lab, Next 10, the California Air Resources Board, and several other government agencies.  The group hopes use the website to connect people through social networking in order to spur action through its “built-in competition system,” said Jones.

Users can create profiles for individuals and for groups, share their progress, and make “pledges” of environmentally-responsible action.

“The most important motivation is our social motivation,” said Jones.  “We are most influenced by what others do and what others perceive of our actions.  So, if your peer group expects you to behave in an environmentally responsible way, you are more likely to.”