More than 400 people jammed into a Portland hotel ballroom Wednesday night to hear a panel of global warming skeptics assert that manmade increases in greenhouse gases are not driving climate change.

The event, hosted by the 150-member

, was open to the general public and drew an attentive and mostly sympathetic audience. Chapter President Steve Pierce asked for a show of hands beforehand, then estimated that 90 percent of the crowd favored the statement that human activities are not the main cause of global warming.

Three Oregon-based panelists -- physicist Gordon Fulks, meteorologist Chuck Wiese and former Oregon state climatologist

-- used long- and short-term temperature measurements and other data to bolster their case.

Skepticism about

was prominent, particularly given a general flattening of temperatures since 1998, a relatively warm El Nino year. Water vapor, sun cycles and natural weather patterns are more powerful in changing climate than increases in carbon dioxide from burning fossil fuels, the panelists said.

"The effects of future changes in CO2 are likely to be modest and manageable," said Taylor, who added that Northwest records do not indicate that temperatures have risen or snowpack has fallen, subjects of

.

The Oregon AMS

after the Oregon Museum of Science and Industry canceled it in November for lack of balance, and the ensuing controversy likely boosted in interest in the event.

"Thank you OMSI," Wiese said, surveying the crowd. "This turnout is absolutely fantastic."

In the question-and-answer period afterward, all but one of the questioners sided with the panelists. Andreas Schmittner, a researcher at Oregon State University who

analyzing the climate's reaction to carbon dioxide levels, was the lone dissenter.

"Most scientists who are actively working in the field have very different opinions than what I've heard tonight," he said. "C02 is a very important driver."

As a national body, the

while the Oregon chapter has decided to take "no formal position" on global warming.

Wiese said water vapor is the main greenhouse gas, and his calculations, which he plans to have peer-reviewed, indicate that carbon dioxide increases can explain at most 8 percent of temperature increases from 1960 to 2011.

The event had no built-in rebuttal. But

published in the journal Science concluded that "ample physical evidence shows that carbon dioxide is the single most important climate-relevant greenhouse gas in Earth's atmosphere."

That was just one of many points stressed Wednesday night. The chapter will post the speakers' presentations, which include charts and data citations, and a video of the meeting on its Web site --

-- in one or two days, Pierce said. The Web site

, run by climate scientists, disputes skeptics' arguments.

--