Here’s a good piece from the press recently, the recession has a positive effect on carbon emissions.
The government are claiming that this helps them reach their C02 targets, as if it were a planned thing, but I guess you take what you can get.
There may well be more mileage in this as an idea, so here are a couple of links:
The Wikipedia entry with some good examples.
Oh, and here’s an academic Journal dedicated to the subject