The planet's biggest problems have to do with sustainability, environmental decline, global poverty, disease, conflict and so forth. Really, they're all interconnected - it's one big problem, which is that the way we're doing things can't go on.

Cities offer us powerful leverage on our most stubborn, wasteful practices. Long commutes in our cars, big power bills from our energy-hogging buildings, shopping trips to buy stuff that'll spend a few short months in our homes and long centuries in our landfills.

For carbon-neutral cities, there are things worth talking about in how our consumption patterns can change - sharing goods, etc. - but those are a fraction of the impacts of transportation and building energy use. If we need to choose priority actions, the most important things are to densify, provide transit, and green the buildings.

There are a lot of different ways of building a prosperous society, and some of them use much less energy than others. And it is possible and more practical to talk about rebuilding systems to use much less energy than it is to think about trying to meet greater demands of energy through clean energy alone.

Many diseases including malaria, dengue, meningitis - just a few examples - these are what we call climate-sensitive diseases, because such climate dimensions for rainfall, humidity and temperature would influence the epidemics, the outbreaks, either directly influencing the parasites or the mosquitoes that carry them.

We can't take climate change and put it on the back burner. If we don't address climate change, we won't be around as humans.

If we brought the mammoth back to Siberia, maybe that would be good for the ecosystems that are changing because of climate change.

Actually, climate change is really about the wellbeing of people. It is not a very vague concept or a vague problem that is out of our everyday lives. It is actually affecting our everyday lives, and this is the fundamental fact that everybody should keep in mind while working toward a low-carbon society.