Impact of the population on the planet is more than a numbers game

LOS ANGELES, CA - APRIL 25: Morning traffic fills the SR2 freeway on April 25, 2013 in Los Angeles, California. The nation's second largest city, Los Angeles, has again been ranked the worst in the nation for ozone pollution and fourth for particulates by the American Lung Association in it's annual air quality report card. Ozone is a component of smog that forms when sunlight reacts with hydrocarbon and nitrous oxide emissions. Particulates pollution includes substances like dust and soot. (Photo by David McNew/Getty Images)

An Earth Day ad released by the Californians for Population Stability focuses on population growth through immigration as a leading cause for the overcrowding, water shortage and traffic in the state.

An Earth Day ad released by the Californians for Population Stability focuses on population growth through immigration as a leading cause for the overcrowding, water shortage and traffic in the state.

But how accurate is this? Are large amounts of people in urban areas significantly affecting the planet in bad way? And how can we know the impact of one group of the population?

Dr. Ellen Percy Kraly is a professor at Colgate University who looks at population and the environment and joined us to talk about the many ways that people influence the earth.