Many accepted scientific facts today started as controversial theories when they were first suggested centuries ago.

The Earth's spherical shape, the concept that planets revolve around the sun instead of the Earth and the existence of atoms are some examples.

New Canaan's G. Warfield "Skip" Hobbs, a geologist and conservationist, said man-made global warming is part of the same list.

"We, the people, the media, our opinion moguls and our elected leaders can no longer ignore the human factor in global change," he said.

Hobbs, who is the president of the New Canaan Nature Center's board of trustees, spoke about the "The Future of Planet Earth" at the New Canaan Library Wednesday, April 23, in observance of Earth Day.

To him, the time to deny the human influence on global warming is over.

Hobbs recognizes that the planet's climate "has always changed," but he said there's no doubt that humans are making it worse.

"Human influences have now overpowered natural forces," Hobbs said.

"On a time scale, the biosphere can adapt, but it takes a long time. And we are upsetting that time scale."

Although the majority of scientists agree that humans have played a big role in global warming, a number of people view it as a threat distant in space and time or claim that the human influence is too small to make a significant impact.

There seems to be little doubt, however, that the climate is changing.

Consequences of the increasingly warmer temperatures include accelerated sea level rise, growing frequency of wild fires, dangerous heat waves, the heightened occurrence of extreme storm and severe droughts.

Hobbs said humans are indeed accelerating global warming by overloading the atmosphere with carbon dioxide, which traps heat and drives up the planet's temperature.

Carbon dioxide comes mostly from the fossil fuels burned for energy, like coal, natural gas and oil.

The geologist said he understands the "privileged" lifestyle in developed countries like the U.S. will not change overnight.

But with global warming and the increasing demand for natural resources, he said the "consequences will be catastrophic" if people don't take immediate action.

"I recognize that 80 percent of our energy comes from fossil fuels, and it isn't going to change anytime soon," Hobbs said. "But we have to start making a transition."

Hobbs said nations should invest more in renewable energy, such as wind, solar and geothermal. Unfortunately, the transition to such energy sources, he said, could cost trillions of dollars over the next 25 years. "There is a cost, but we have to pay more for our energy," he said.

Another alternative to fossil fuels Hobbs believes is under-explored is nuclear energy. "Nuclear is OK. Everybody is scared about it, but it is green."

As president of the American Geological Institute, Hobbs was a member of the Council of Scientific Society Presidents in Washington, D.C., from 2009 to 2012.

He said he understands how society, especially in this part of the country, is used to a comfortable living standard, but he said "we take our modern conveniences for granted."

"A modern society has demands," Hobbs said. "But we create an awful lot of waste. We're not good custodians."

Part of the problem, according to Hobbs, is the fact that many leaders deny the human role in global warming. "Politicians don't want to take on controversial policies," he said.

What makes it worse is that developing countries look at the American lifestyle and want to reach the same standard, Hobbs said. He noted that several Asian countries, especially China, are undergoing multiple construction projects as they make the shift "from a rural to a city culture."

While spending the last 44 years in the oil, gas and mining-exploration business, Hobbs has seen some of the best and the worst places on Earth.

"I've been all over the world," he said. "I've seen some of the most magnificent, remote places on Earth. I've also seen the most horrific scars, from oil-covered swamps in Indonesia to horrible mining waste in Colombia."

What he saw has left him concerned about the future of the planet. Hobbs said humans should treat the world like they treat their own homes.

"We have to leave this Earth in a better place than where we found it," he said. "As a geologist, I'm very concerned ... We need to wake up."

Hobbs is also the president of the New Canaan-based Ammonite Resources, an international energy and mineral resource consulting firm.

First Selectman Robert Mallozzi, who introduced the geologist at the lecture, said New Canaan is proud to have Hobbs in town.

"Skip really does personify what we all come to love about New Canaan, that is, a group of passionate folks living in the community that want to share their knowledge, their affection of what they love, with us," Mallozzi said.

The first selectman's view of the future seemed more optimistic than Hobbs'.

"I really do feel that there will be a greater effort, and certainly much more sensitivity to (environmental issues) from the folks coming behind us than there was 50 years ago," Mallozzi said, referring to younger generations. "It just wasn't a big part of my upbringing. It's now a big part of our kids' upbringing."

Though Hobbs is worried about the future, he agrees that future generations will be more educated about the environment.

"We have made a huge impact on Earth, and the consequences are going to be very disrupting and severe if we don't do something about it," Hobbs said. "But we'll get through it. Humans will survive. We're not going to become extinct."; 203-330-6582; @olivnelson