U.S., China ratify Paris climate deal, setting stage for G20

China and the UnitedStates ratified the Paris agreement to cut climate-warmingemissions on Saturday, marking a major step toward the enactmentof the pact as early as the end of the year and setting thestage for other countries to follow suit.

The world's two biggest emitters of greenhouse gases madethe landmark announcement as heads of state from the Group of 20biggest economies, or G20, arrived for a summit in the city ofHangzhou, parts of which resembled a ghost town as Chinesesecurity locked down the area.

U.S. President Barack Obama's last scheduled trip to Asiabefore leaving office however got off to an awkward start. Soonafter Air Force One landed, a Chinese security official blockedNational Security Adviser Susan Rice on the tarmac, speakingangrily to her before a Secret Service agent stepped between thetwo.

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China has gone to great lengths to try to make the Sept 4-5G20 summit a success, hoping to cement its standing as a globalpower, but a range of thorny diplomatic topics could overshadowthe agenda.

G20 leaders are likely to renew their promises to use taxand spending policies to invigorate the sluggish world economy,although a new pro-growth push was unlikely.

Overcapacity in the global steel industry, a sore point forChina as the world's largest producer of the metal, barriers toforeign investment and the risk of currency devaluations toprotect export markets will also figure in the discussions.

Beyond economics, there may be friction over territorialdisputes in the South China Sea and a U.S.-South Korea decisionto deploy a missile defence system in South Korea to countermissile and nuclear threats from North Korea.

U.S.president will raise human rights issue

When Obama met Chinese President Xi Jinping, he told himthey would have candid talks on cyber, human rights and maritimeissues.

Nevertheless, the climate deal set a positive tone.

"Just as I believe the Paris agreement will ultimately proveto be a turning point for our planet, I believe that historywill judge today's efforts as pivotal," Obama said after he andXi handed ratified documents to UN Secretary-General BanKi-moon.

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"We have a saying in America that you need to put your moneywhere your mouth is. And when it comes to combating climatechange, that's what we're doing. Both the United States andChina, we're leading by example."

At a joint ceremony, Xi said it "speaks to the sharedambition and resolve of China and the United States inaddressing global issues."

French President Francois Hollande said it was an importantstep that would pave the way for the implementaton of the Parisagreement at the end of the year.

People leave in droves, city quiet for summit

The stakes are high for China to pull off a trouble-free G20summit, its highest profile event of the year, and security inHangzhou was intense.

Volunteer security agents prevented journalists from filmingin deserted parts of the normally bustling city of 9 million during theweek-long holiday for the summit. Theyshut down the city's famousWest Lake beauty spot and offered free travel vouchers worth upto 10 billion yuan ($1.5 billion US) to encourage people to visitout-of-town attractions.

More than 200 steel mills in surrounding districts were shutas part of a bid to limit pollution.

With the summit wedged in between the Brexit vote and theU.S. presidential election, G20 leaders will be keen to mount adefence of free trade and globalization.

Central banks 'close'to limits on stimulation

Concerns about subduded growth will be a major concern.

The world's biggest economies have pulled out the monetarypolicy stops to promote growth, but central banks are now"pretty close" to the limits of their ability to stimulateeconomies, said Angel Gurria, head of the Organization forEconomic Co-operation and Development (OECD).

In the absence of "breakthrough, collective" policies,global growth was likely to remain weak, he told Reuters.

"We have left our good central bankers to do all the heavylifting."

In separate remarks to Reuters, Pascal Saint-Amans, thedirector of the OECD's Centre for Tax Policy and Administration,addressed the thorny issue of multinational corporate taxliability, which the European Commission's recent decisionagainst Apple Inc has brought into sharp relief.

The European Commission said this week that Apple owed up to13 billion euros ($14.50 billion US) in back taxes to Ireland,based on existing regulations, a decision that both Apple andIreland, which relies on low taxes to attract investment, havevowed to fight.

China is using the G20 to push its diplomatic agenda with araft of bilateral meetings.

China and Turkey pledged earlier in the day to boostcounter-terrorism ties, setting aside previous disagreementsover China's treatment of a Turkic-speaking Muslimminority.