Students and faculty of Oxford College joined those of more than 1,500 other colleges and universities in the nation's largest teach-in in United States history on Thursday.

The event, called Focus the Nation, ended with a meet-and-greet session and presentation by National Geographic photographer Peter Essick.

Essick, along with a team of writers who produced a three-part series for National Geographic on climate change in 2004, presented the group with photos and shared insight on what those photos mean in relation to global warming.

"When we first talked about the story we said, 'If global warming is real then we should be able to photograph it,'" Essick said.

The story was divided into three parts - physical changes, eco changes and past and future changes. Essick presented his photos in that order to show the effects of climate change on the various aspects of the environment.

Essick told those in attendance humans really did not begin to impact the environment until the industrial revolution began in 1750 and the use of coal to produce goods began.

"When we started using coal you can start to see our influence in the atmosphere," Essick said. "Not until the 1950s, when we started using oil, driving cars and experiencing large population growth did we start seeing a major impact."

He said a scientist began recording carbon dioxide levels climbing in the atmosphere in 1957.

Through time, Essick said, things like deforestation and increased consumption have led to more carbon dioxide in the atmosphere.

The physical effects on the earth, Essick said, are evident in many ways - all of which he photographed in location all over the world.

"We've started to see melting of glaciers all over the globe," Essick said. "We're also experiencing more forest fires in northern forest as a result of the climate change."

Ecologically, climate change has affected animal and plan life, according to Essick.

"Planting zones have changed in the U.S.," Essick said as he presented an illustration of the United States' planting zones. "Here in Atlanta, we have moved up one entire zone. I've started seeing more and more tropical plants in nurseries around here."

 Essick said the physical and ecological changes have a bearing on Earth's future and sooner than many think.

"We will see a warmer summer index by around 10 degrees in the next 50 years," Essick said. "Scientists also believe we will see more extreme weather events (like monsoons and hurricanes)."

Two Princeton professors have developed stabilization wedges that provided proposed answers to solving the world's carbon dioxide excess in the next 50 years. Essick said the scientist believe that by adhering to the guidelines in the stabilization wedges that Earth can be made as stable as it is now.

"Scientists think we need to do it quickly," Essick said. "What we're doing now will stay around for a long time. If we stop now we may be able to maintain but that's with doing everything in the wedges and we still don't know what effect that will have on the environment."