Climate Change Summit kicks off

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The highest-level conference yet on climate change has opened in New York. 100 world leaders gathered at the UN to try to jumpstart stalled negotiations toward a global climate pact.

U.N. Secretary-General Ban Ki-moon called on presidents, prime ministers and other leaders "to accelerate the pace of negotiations." He urged them to "strengthen the ambition of what is on offer" for a deal at the world climate conference in Copenhagen, Denmark in December.

Much attention is fixed on U.S. President Barack Obama's first U.N. speech. He said the United States is "determined to act."

Also addressing the opening session of the summit, Chinese President Hu Jintao called for stronger international efforts. He introduced the latest measures China is taking.

Hu Jintao, Chinese President, said, "China will develop renewable and nuclear energy greatly. We will endeavor to increase the share of non-fossil fuels for primary energy consumption to about 15% by 2020."

Tuesday's U.N. summit seeks to add pressure on rich nations to commit to greenhouse gas cuts and to pay for poorer nations to burn less coal and preserve their forests.

Major economies are expected to spell out national plans for billions of people and their households, businesses and farms in the decades ahead.