Jose Gomez-Ibanez studied the amount by which people living closer together - and driving less - can reduce the CO2 emissions to help global climate change.
Hania Zlotnik, director of the UN population division, talks about the economic challenges for a future with an aging population, and an encouraging sign.
Jean Decety, a neuroscientist, studies human empathy. He talked to EarthSky on his study on how children with aggressive conduct disorder process empathy.