Chinese President Hu Jintao's speech at the UN climate change summit Tuesday on China's efforts to curb greenhouse gas emissions has been applauded by world leaders, officials and experts.

UN Secretary-General Ban Ki-moon expressed appreciation to China's new proposal. "I think that anyone who still doubts their sincerity on climate change needs to take another look. China realizes the impact that climate change has and that they must act," Ban said.

In his address, Hu said China will intensify effort to conserve energy and improve energy efficiency, and endeavor to cut carbon dioxide emissions per unit of gross domestic product (GDP) by a "notable margin" by 2020 from the 2005 level.

Former U.S. vice president and environmental activist Al Gore praised on Tuesday China's efforts the country has devoted to tackle climate change.

"It's not widely known in the rest of the world but China in each of the last two years has planted two and half times more trees than the entire rest of the world put together," he noted.

He believed Hu's remarks could point to more actions.

The Chinese president said at the summit that China will adopt to further integrate actions on climate change into its economic and social development plan.

Current President of the UN General Assembly Ali Treki on Tuesday said Hu's remarks were of great importance to global efforts on climate change and to the success of the Copenhagen Conference.

He also appreciated China's concrete measures to fight climate change and the contributions it had made so far.

U.S. Senator Joe Lieberman described Hu's pledge to reduce CO2 emissions growth by a "notable margin" by 2020 from China's 2005 levels as "a very significant and encouraging step."

China's new pledge may also help rally support at the U.S. Senate for legislation to battle climate change, he added.

Andrew Deutz of the Washington-based Nature Conservancy said China's announcement was "a step in the right direction."

"China is creating expectations for Copenhagen, even if it has not delivered yet," he said.

Greenpeace China climate change campaign manager Yang Ailun said Hu's speech was a positive sign that China was serious about fighting climate change, as it "has publicly confirmed that China would have a carbon emissions reduction target."

Oxfam Hong Kong campaign coordinator Stanley So also praised Hu for showing "willingness" to take on responsibility for reducing emissions.

In his address, Hu said China would cut carbon dioxide emissions per unit of GDP by a "notable margin" by 2020 from the 2005 level, and would vigorously develop renewable and nuclear energy.