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 yesterday for Hangzhou, China, where he will meet today 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 US 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 US, 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 US or China.
That won't happen until a critical mass of polluting countries joins. Aiming to build on previous cooperation, the US 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 US 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 US 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.
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