More than 140 countries have gathered at the United Nations for a summit on climate change. U.N. Secretary General Ban-Ki moon says the earth's warming is an urgent, global challenge that requires unprecedented leadership and immediate action. From U.N. headquarters in New York, VOA's Margaret Besheer has more.

In his opening address to the summit, Mr. Ban said he is convinced that climate change, and what the international community does about it, will define our era and the global legacy we leave for future generations.

"Today, the time for doubt has passed," he said. "The United Nations Intergovernmental Panel on Climate Change has unequivocally affirmed the warming of our climate system, and linked it directly to human activity."

Experts say 11 of the past 12 years rank among the warmest in global surface temperature in more than 150 years. Such warming has serious consequences for the earth, causing glaciers to melt more rapidly, sea level to rise, and puts some plant and animal species at increased risk of extinction.

The secretary-general pointed out that the effects of climate change are worldwide, but often impact developing countries the most, even though they have contributed the least to the process. But he said global warming does not have to be a serious threat to development.

"By being creative, we can reduce emissions while promoting economic growth," he said. "This is our opportunity to advance sustainable development; encourage new kinds of cleaner technologies, industries and jobs; and integrate climate change risks into national policies and practices."

Speakers at the summit include former U.S. Vice President Al Gore, German Chancellor Angela Merkel and French President Nicolas Sarkozy. Secretary of State, Condoleezza Rice, will speak at one of the sessions.

President Bush, who has long opposed negotiated limits on the greenhouse gases blamed for global warming, will not participate in the day's meetings, but will attend a dinner later.

Secretary-General Ban organized the one-day summit on the sidelines of the 62nd General Assembly to build political momentum before a U.N.-sponsored climate change conference in Bali in December. That meeting aims to launch negotiations for an emissions -reduction agreement to succeed the Kyoto Protocol in 2012.