Czech President Vaclav Klaus sharply criticized a U.N. meeting on climate change on Tuesday at which U.S. President Barack Obama was among the top speakers, describing it as propagandistic and undignified.

"It was sad and it was frustrating," said Klaus, one of the world's most vocal skeptics on the topic of global warming.

"It's a propagandistic exercise where 13-year-old girls from some far-away country perform a pre-rehearsed poem," he said. "It's simply not dignified."

At the opening of the summit attended by nearly 100 world leaders, 13-year-old Yugratna Srivastava of India told the audience that governments were not doing enough to combat the threat of climate change.

Klaus said there were increasing doubts in the scientific community about whether humans are causing changes in the climate or whether the changes are simply naturally occurring phenomena. But politicians, he said, seem to be moving closer to a consensus on climate change.

"The train can't be stopped and I consider that a huge mistake," Klaus said.

U.N. Secretary-General Ban Ki-moon organized the climate summit to help create momentum before a U.N. meeting in Copenhagen in December to reach agreement on new targets for reducing so-called greenhouse gas emissions.

However, new proposals by China and a rallying cry from U.S. President Barack Obama did little to break a U.N. deadlock about what should be done.

Klaus published a book in 2007 on the worldwide campaign to stop climate change entitled Blue Planet in Green Chains: What Is Under Threat -- Climate or Freedom? In the book, Klaus said global warming has turned into a new religion, an ideology that threatens to undermine freedom and the world's economic and social order.