I didn't hear the NPR interview, so I don't know how the speaker was imagining a per-person carbon footprint. If you count just the things an individual is directly responsible for, like personal transportation and home energy use, maybe (maybe) you could get your footprint down to one ton. In general, these are the kinds of things measured by the personal carbon calculators out there.

But if you use a more complete calculation, which includes a share of the emissions you benefit from (businesses whose products you buy, government services like libraries and police), MIT students have found that the lowest carbon footprint an American can have is 8.5 tons. However, this kind of calculation works in a top-down fashion (total emissions from all sectors divided by population) and wouldn't be very easy to calculate - or change - for individual people.

Don't be discouraged, though. All this shows is that it will take both individual and institutional changes to reduce our overall carbon footprint. In a democracy, institutional changes don't usually happen until individuals have proven those actions doable and effective. So good luck with the diet!

to chime in again...

For people really serious about reducing their carbon footprint, one potential weakness with many of the carbon calculators out there is that they're snapshots - you can't track your reductions like you might with an actual diet (stepping on the scale periodically to see how you're doing). The UK has a head start on the US for sites that let you track your footprint over time, though there's at least one business-focused site in the US. Here are the ones I'm aware of:

Edenbee (UK)
Carbon Diet (UK)
OpenEco (US, business-focused)

Having just gone through the process of trying to figure out exactly what we need to do to reduce our carbon footprint, let me recommend a couple of easily available sources that will give you a list of things to do.  Yes! magazine, Spring 2008 issue, has a short article about a fairly typical family reducing their footprint in 10 years.  This is the easy stages approach. The link is http://www.yesmagazine.org/article.asp?id=2287.    Second, I found The Carbon Buster's Home Energy Handbook by Godo Stoyke to be concise and informative.  There's a 2 page list of things to do, actually 2 lists: one for optimizing money saved, and the other for optimizing carbon reduction.  So if you don't want to calculate, just flip to the lists and start doing the items.  If you want to know why and how much without calculating it all yourself, the rest of the book has that info.  I checked it out of the King County Library, and have now added it to my Amazon wish list to be purchased Real Soon Now.

Another site to check out is the Riot for Austerity - 90% Reduction Page. This is a group that is commited to reducing their envioronmental impact to 90% of the average American's (Monbiot's estimate for achieving 350 ppm of carbon in the atmosphere).

It's in seven categories (Transportation, Electricty, Heating, Water, Trash, Food, and Consumer Spending) that attempt to cover the vast majority of your impact. There are goals, guidelines, and a yahoo group.

http://www.riot4austerity.org/blog/?page_id=2

The Nature Conservancy offers an easy-to-use carbon footprint calculator that is both validated by science (we use a lot of EPA data and validate all of our sources) and includes indirect emissions, which makes it the most accurate carbon calculator on the web today.

http://www.nature.org/initiatives/climatechange/calculato ...

Unfortunately, carbon footprints are a bit of a tricky business.  The first issue is that you're dealing with approximations and averages, so even detailed footprint calculators have to infer a significant amount of data.

The second, more critical issue, is that few calculators use life cycle assessments---they instead just collect data from directly attributable data (home energy use, driving and flying).  The reason why is because it's very difficult to even estimate the carbon footprint of all kinds of lifestyle/indirect impacts: everything from drinking water to plastic bags to computers, manufacturing cars, etc.  The data is simply not there yet.

In terms of good calculators out there.  I would first recommend University of Berkeley's LCA calculator: http://bie.berkeley.edu/calculator.  It makes a valiant attempt at integrating all of those indirect co2e emissions we're all responsible for.  

A few others that include recommendations for actions to take to reduce your impact are below:
Make Me Sustainable: http://www.makemesustainable.com
Earthlab: http://www.earthlab.com
Yahoo Green: http://green.yahoo.com/calculator

The last three are part of "pledge" sites, which allow you to choose certain actions you can take and track your footprint reductions over time.

The unfortunate thing with these is that they don't really walk your through the process.  Umbra's reference to weight loss programs is very apropos. I've been working with some local Bay Area groups to launch a campaign that utilizes the best of the web and the support of real-life networks to help people make reductions that are achievable and relate to their lifestyles.  It's called Climate Relay: http://www.climaterelay.org.

Hope that helps,

Asher

Working out an appropriate level for per capita emissions is challenging. I took a stab at it here.

There are questions both about the physical nature of the world and about the ethical basis for distribution. There are also questions about how quickly we can or should make the transition. An individual can abandon society and live in the woods, but to transition to a sustainable society requires infrastructure changes that will take decades.

Also: Per capita emissions and fairness

"Everybody knows that emissions in the developed world are too high...

What is less often acknowledged is that emissions in the developing world are already too high. Chinese per capita emissions are 3.9 tonnes, while those in India are 1.8. The list of countries by per-capita greenhouse gas emissions on Wikipedia shows three states where per-capita emissions are below 750kg: Comoros, Kiribati, and Uruguay. Even the average level of emissions for sub-Saharan Africa is almost six times above the sustainable level for our current world population."

Well i have tried all the fad diets and the only thing that realy worked was NLP Hypnotist what have you got to lose a few pounds of pork i can now fit into a size 10 it helps stop the cravings.