PORTLAND, Ore. -- A heated evening in downtown Portland brought out both sides of the global warming issue Wednesday.

Former Vice President Al Gore spoke at Keller Auditorium to promote his new book on climate change. During the show, hundreds of people gathered across the street to rally against his message.

Members and supporters of the Americans for Prosperity group held up signs to expose what they believe are the extreme economic costs behind federal climate change policies.

Meanwhile, Gore supporters packed the auditorium and gave the former vice president a standing ovation.

"When you multiply 6.8 billion people times the power of these few technologies, we have a very dramatic impact on the ecosphere," Gore said during his lecture.

Mary Ellen Burke of Americans for Prosperity, said the environment needs to be debated on its own terms.

"We just don't want them to disguise a tax and more government regulation under environmental concerns," Burke said.

There was no violence reported near the auditorium.

On early Wednesday morning, police discovered vandalism on the Keller Auditorium believed to be related to Gore's message. The vandals spray-painted messages such as: "Change the system, not your light bulb" and "Don't buy false solutions" on the building.

The Americans for Prosperity group condemned the vandalism.

Protesters Chant 'Al Gore Is A Liar'