While a large number of people, including some scientists, believe that we are in an unprecedented period of global warming caused primarily by humans, Dr. James Koermer, a meteorology professor at Plymouth State University, would beg to differ.

During a presentation at the university on Wednesday, Koermer explained why there are a growing number scientists, such as himself, who don't subscribe to the popular theory on global warming.

Koermer said the Earth's climate has always changed and has experienced alternate warming and cooling trends long before the dawn of man.

Koermer said most research suggests that at the beginning of the last millennium, there was a global warming period that ended around 1600, when a significant cooling trend — which he called a mini ice age — lasted for approximately 100 years.

The most recent global warming trend picked up during the 1700s, which coincides with the start of the Industrial Age, Koermer said.

Going back millions of years, some research suggests the Earth has had much more extreme climate changes than are occurring today.

"Over millions of years there have been periods when we have been hotter than we are today," Koermer said.

He added that while humans do have an impact on the climate, it is minimal compared to natural phenomena. He also said that humans are not the biggest producers of carbon dioxide and that the gas is not the most abundant green house gas in the atmosphere. That title goes to water vapor, which is produced by the world's oceans.

Koermer said that water vapor is responsible for 95 percent of the green house gas effect in a given year while another 4.72 percent is caused by a mix of other greenhouse gases, including methane, nitrous oxide and carbon dioxide, which are naturally produced.

Humans are only responsible for .28 percent of all greenhouse gases produced during a year, he said.

GUAY/STAFF PHOTO DR. JAMES KOERMER, a meteorology professor at Plymouth State University, gives a presentation on the "inconvenient science" that, in his opinion, debunks popular theories on global warming.

Koermer said just because he doesn't think man-made carbon dioxide is contributing significantly to climate change, it does not mean he is opposed to the increased use of renewable fuel sources. He said that fossil fuels are a limited resource, so finding alternatives is necessary.

Koermer said scientists are not yet sure what has caused climate change in the past, but factors may include shifts in the Earth's axis as well as changes in the orbit of the Earth around the sun. Over time, Koermer said, the Earth's yearly path around the Sun changes from circular to more elliptical before changing back.

Sunspots and solar flares may also effect the Earth's climate. Koermer said solar flares and spots seem to increase and decrease on an 11-year cycle. He noted that there was a marked decrease in solar flares during the mini ice age of the 1600s.

Changes in the wind patterns or atmospheric oscillations can affect global climate. The El Niño and La Nina weather patterns are an example as well as the Pacific Decadal Oscillation.

"[The Earth's climate] has been swinging up and swinging down and we don't know why, we don't know what caused the last ice age," Koermer said after the presentation.

Koermer said that the long-range climate models proponents of global warming often use are inaccurate.

He said the most sophisticated weather prediction models are only accurate up to weeks and most meteorologists hesitate to forecast much beyond six days.

He said just as climate prediction models aren't flawless, the methods used to estimate past temperatures, such as examining tree rings, sediment layers and ice cores, are not fool proof and are limited in what they prove.

Kevin McGuire, a fellow professor at PSU, said Koermer's presentation was "very well done."

"I agree that there are a lot of uncertainties," McGuire said about the causes and nature of global climate change.

"I agreed with some aspects," Katie Laro, PSU freshman and meteorology major said. "Like, how can we can know for certain that the average temperature will increase or decrease 100 years from now?"