Compact communities fight climate change. We've said it before, but now Clark points us to some incredible visual evidence: CO2 maps of major cities, which show that, in general, the denser a neighborhood, the less the climate-changing impact of people who live there:

What can we learn from these maps? Our personal transportation choices can and do impact greenhouse gas emissions and global climate change. Households in the city have easier access to public transportation systems, drive less often or shorter distances, and walk or bike to their destinations. With continued investment in public transit and in walking- and biking-friendly neighborhoods, cities can further reduce greenhouse gas emissions and improve local air quality.

Of course, density in and of itself is not neccessarily better. The point is not how close together the houses are, but rather what that compactness -- when combined with other livability measures, smart growth, transit and walkshed technologies -- can let us create: brighter, greener cities.