CO2 emission is about as directly related to income as caloric intake is. Past a basic threshhold, you could easily double or halve the one while holding the other constant. It depends on your concrete consumption practices rather than your abstract income.
"you seem to be conflating expenditures with income. ... practices that lower personal CO2 emissions could just easily lower personal expenditures, e.g. switching from the car to the bus. You might argue that quality of life went down in such a case, but that's a different thing from lowering wages, real or nominal."
Sorry, I was assuming a Marxist framework on wages, as being set by the value of labour power, meaning the basket of consumption goods that go to reproduce it. Allowing that this is socially fixed, a habitual shift to reduce expenditure would eventually lead to a lowering of the price of labour power.
More likely of course is that travelling on the bus would fail to reproduce your labour power at the level that social relations expected, namely, you'd be too often late for work, and fail to command a high wage. In Britain - as I suspect in the US - the profile of bus users is low income, and they are punished for their low earning potential by wasting an inordinate amount of time on the bus.
Barry picked out an interesting culprit for CO2 emissions that is typical, air-travel. In the last thirty years, regular air-line travel has come within the range of American and European pockets. From a green scaremongering perspective this is a big problem. So who's first in giving up travel abroad (or even cross country for Americans)? Not me. -- James Heartfield The 'Death of the Subject' Explained is available at GBP11.00, plus GBP1.00 p&p from Publications, audacity.org, 8 College Close, Hackney, London, E9 6ER. Make cheques payable to 'Audacity Ltd'