Hmm. I didn't get the right answer. 

Maybe that's a reason for going for something as unambiguous as infinity 
miles per gallon? For those of you who didn't get it, that's zero 
carbon, or, as Cuban permaculturist Roberto Perez said when I asked a 
question at a meeting he was addressing in London on Tuesday, we 
shouldn't use this word 'carbon', talk about zero fossil fuels instead. 
(By the way, he is interested in the Zero Carbon Caravan to Copenhagen 
next year.  Does anyone know someone with a yacht he could travel across 
the Atlantic on?)

Zero carbon (or zero fossil fuels) is something the Centre for 
Alternative Technology are promoting. They did a zero carbon Britain 
report last year <> and are currently doing a 
zero carbon Europe report.  They dispense completely with fossil fuels, 
and indeed all liquid fuels, which gets rid of biofuels, reduce cars by 
two thirds, and use renewable electricity to power the remaining third.  
I think we should be pushing electric cars and forget about everything 
else, including high mpg, hybrids, fuel cells, hydrogen, biofuels


George Marshall wrote:

>       Very interesting (I think) that small tweaks in language produce
>       shifts
>       The mpg confusion
> What reduces emissions more?
> *A.* Someone swapping their old SUV (which gets 12 miles per gallon) 
> for a hybrid version (18 mpg) or
> *B.* someone upgrading their 25 mpg compact to a new 46 mpg Prius?
> (ignore for a minute manufacturing issues or driving habits and assume 
> the miles driven are the same).
> The surprising answer (for those who don't work it out) is A. It's 
> easy enough to see why this is the case. If the driving distance is 
> 100 miles, then for case A the saving in fuel used (and hence 
> emissions) is 100/12-100/18 = 2.8 gallons, while for B, you have 
> 100/25-100/46 = 1.8 gallons. The confusion arises because people like 
> to think linearly about numbers, not inversely, and so tend to assume 
> that a similar change in mpg has a similar impact on fuel usage. This 
> is not however the case - improvements in efficiency at the low end of 
> the scale are much more useful at reducing emissions. This is actually 
> a very general point - when trying to raise efficiency it is always 
> sensible to start with the least efficient processes.
> This confusion got some attention 
> <> 
> a couple of months ago after a piece that was published in /Science/ 
> by Larrick and Soll 
> <>. 
> They tested peoples instinctive reactions to changes in mpg numbers 
> and found that people very often got it wrong, leading to less than 
> optimal decisions. They also tested a different way of giving fuel 
> usage information (the number of gallons used per mile), and since 
> this is linear in emissions, people made the correct judgment much 
> more often (it's worth noting that the standard in most of Europe is 
> already litres per 100 km). Rewritten in those terms, the choices 
> above become:
> *A.* Someone swapping their old SUV (which takes 8.3 gallons to go 100 
> miles) for a hybrid version (5.6 gallons/100 miles) or
> *B.* someone upgrading their 4 gallons/100 miles compact to a new 2.2 
> gallons/100 mile Prius?
> Much easier, right? The authors 
> <> of 
> the Science piece are trying hard to get US manufacturers and the EPA 
> to switch over from mpg to this new standard (though they prefer 
> <> gallons/10,000 miles). It all seems 
> eminently sensible to us
>George Marshall,
>Director of Projects,
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