HONOLULU (AP) -- Opening his final trip to Asia, President Barack Obama is expected to join Chinese leader Xi Jinping in announcing their countries are formally taking part in a historic global climate deal. Yet thornier issues like maritime disputes and cybersecurity shadow Obama's visit.

The president departed Friday for Hangzhou, China, where he will meet on Saturday with Xi ahead of a summit of the Group of 20, a collection of industrial and emerging-market nations. Environmental groups and experts tracking global climate policy said they expected the two leaders would jointly enter the sweeping emissions-cutting deal reached last year in Paris. Unlikely partners on addressing global warming, the U.S. and China have sought to use their collaboration to ramp up pressure on other countries to take concrete action as well.

Entering the climate agreement has been an intricate exercise in diplomatic choreography. The deal was reached in December, and the U.S., China and many others signed it in April, on Earth Day. Even the third step -- formally participating in the deal -- doesn't bring it into force in the U.S. or China. That won't happen until a critical mass of polluting countries joins.

Aiming to build on previous cooperation, the U.S. and China have also been discussing a global agreement on aviation emissions, though there's some disagreement about what obligations developing countries should face in the first years. The aviation issue is expected to be on the agenda for Obama's meeting with Xi, along with ongoing efforts to phase out hydrofluorocarbons, another greenhouse gas.

The alliance on climate has been a rare bright spot between the U.S. and China in recent years, a relationship otherwise characterized by tensions over China's emergence as a key global power. Washington  has been deeply concerned about China's territorial ambitions in waters far off its coast, while Beijing looks warily at Obama's efforts to expand U.S. influence in Asia, viewing it as an attempt to contain China's rise.

Obama, in a CNN interview, said he'd told China's leaders repeatedly that with more global power comes more responsibility.

"Part of what I've tried to communicate to President Xi is that the United States arrives at its power, in part, by restraining itself," Obama said. "When we bind ourselves to a bunch of international norms and rules, it's not because we have to, it's because we recognize that over the long term, building a strong international order is in our interests."

Of China's artificial island-building in the South China Sea, Obama added: "We've indicated to them that there will be consequences."

Though Obama had early hopes for forming a close personal and professional relationship with Xi, who took office in 2013, many in Washington have been surprised by the Chinese leader's nationalist inclinations as president. The two countries have made little progress reconciling their differences over human rights and Chinese cyber spying, issues the White House said Obama planned to raise.

As for its commitments to the climate deal, the U.S. pledged to cut its emissions 26 percent to 28 percent over the next 15 years, compared to 2005 levels. China vowed that its emissions, which are still growing, will top out by 2030.

Before the deal takes effect, 55 countries representing 55 percent of the world's emissions must formally join. Entrance by the U.S. and China will get the deal to about 40 percent of emissions. Fewer than half of the requisite 55 countries will have joined, but many others have signaled they plan to join in 2016, and the White House has been hopeful the deal can take force before year's end.

During three days in China, Obama will also attend an economic-focused gathering of G-20 leaders and hold his first meeting with Turkish President Recep Tayyip Erdogan since a failed coup attempt against his government this summer. Obama also will meet with Britain's new prime minister, Theresa May. Then the president travels to Laos for the first visit by a sitting president. Obama plans a major speech on his Asia policy and a meeting with the new Phillipine leader while in Laos.

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