In an announcement issued as the two leaders met in California, the White House said the two leaders "have agree on an important new step to confront global climate change."
"For the first time, the United States and China will work together and with other countries to use the expertise and institutions of the Montreal Protocol to phase down the consumption and production of hydrofluorocarbons (HFCs), among other forms of multilateral cooperation."
The statement said phasing down HFCs globally has the potential to "reduce some 90 gigatons of CO2 equivalent by 2050, equal to roughly two years worth of current global greenhouse gas emissions."
HFCs are commonly used in refrigerators, air conditioners and industrial applications -- and are becoming more commonly used as a substitute for ozone-depleting substances being phased out under the Montreal Protocol on Substances that Deplete the Ozone Layer, the statement said.
HFCs do not deplete the ozone layer, but many are potent greenhouse gases, the statement said.
Obama said Friday cybersecurity and rules for dealing with it will grow in importance as the United States and China develop their relationship.
Speaking at a joint news conference with Xi during informal talks in California, Obama said the increasing use of computers would require new rules, The New York Times reported.
He termed the issues surrounding cybersecurity "uncharted waters," and said it is critical "to arrive at a firm understanding of how we work together on these issues."
Computer-driven attacks were a matter of international concern, he said, and required "common rules of the road."
Obama separated the controversy over the National Security Agency gathering telephone data on Americans from cyberattacks on U.S. companies and federal agencies. The cyberattacks are about "theft and hacking," he said, while the NSA actions are concerned with "identifying potential terrorists or criminals."
Xi noted recent media attention to cyberattacks had created the sense they originated mainly from China and that cybersecurity was "the biggest problem in the China-U.S. relationship."
Without directly addressing those reports, the Chinese leader said "we need to pay close attention to this issue and study ways to effectively resolve this issue."
He said the two nations could work "in a pragmatic way" to address the problem and noted a working group had been established to discuss cyber security issues.