US President Barack Obama on Monday called on the Chinese and US governments to strengthen cooperation in dealing with such global challenges as climate change.

"There are very few global challenges that can be solved unless China and the United States agree," he stressed while answering a question at a town hall with Chinese students in Shanghai, the first stop of his four-day China tour.

As the world's two largest greenhouse gas emitters, the United States and China should assume the responsibility to curb greenhouse gas emissions, he said.

"Unless both of our countries are willing to take critical steps in dealing with this issue, we will not be able to resolve it," Obama said.

The president called on world leaders to strike a deal at the December Copenhagen conference during which they would make differentiated commitments to reducing greenhouse gas emissions.

China should not take the same obligations as the United States since it has a much larger population living in poverty, he said.

Climate change is expected to be one of the main topics at the upcoming meeting between Obama and Chinese President Hu Jintao.

President Hu promised at a September UN climate summit in New York that China would cut carbon dioxide emissions per unit of gross domestic product by "a notable margin" by 2020 from the 2005 level.

Obama has said he wants to cut US emissions back to 1990 levels by 2020 and 80 percent further by 2050, but the US Congress was unlikely to complete climate legislation by the time of Copenhagen, due to great political challenges in the midst of a recession with high unemployment and other domestic priorities.

According to US top negotiator Jonathan Pershing, it would be difficult for the US to pledge an emissions target without legislation by Congress, therefore a new pact to combat global warming is a forlorn hope for Copenhagen.

The Dec. 7-18 Copenhagen meeting, which is expected to bring together leaders from 190 countries, aims to renew greenhouse gas emissions reduction targets set by the Kyoto Protocol, due to expire in 2012.