From EcoGeek here are a couple of related news items that you can take as you see fit:
First: A new study from NASA’s Goddard Institute for Space Studies has identified on-road transportation as the most significant overall source contributing to global warming. Power generation, while having the greatest total impact, also includes a large number of compounds that increase cloud reflectivity and provide other effects to offset some of the warming they are responsible for. More here.
Second: Google Maps adds bicycle information for cyclists in 150 cities including Portland.