Russia's Cold War-style standoff with the West sent a chill through G20 summit talks on Saturday, as an ambitious new push on climate change undermined host Australia's focus on action to heat up the world economy.
Along with the Ukraine crisis, a surprise pact by the United States and China on global warming has upset Australian Prime Minister Tony Abbott's desire to emerge from the Brisbane summit with a singular focus on reviving economic growth around the world.
President Barack Obama said the Sino-US breakthrough in Beijing this week on reducing carbon emissions proves that a post-Kyoto deal to arrest climate change is achievable, as he unveiled a $3 billion pledge to a UN-backed climate mitigation fund.
"If China and the US can agree on this, then the world can agree on this -- we can get this done," he said in a speech in Brisbane.
Obama also said the United States cannot "carry the world economy on our back", urging G20 leaders to work harder to create jobs by revving up growth in the aftermath of the worst financial crisis since the 1930s.
Addressing the G20 conclave, Abbott ticked off a list of geopolitical challenges ranging from instability in eastern Europe and the Middle East to Ebola in west Africa and fragile economic growth.
"This is the world's work that we are engaged on," he said, reminding the G20 leaders that together their countries amount to 85 percent of the planet's gross domestic product and 65 percent of its population.
"But the message that should come from us over these next two days is a message of  hope and optimism. Yes, our world can grow and, yes, our world can deliver the jobs that our people want," Abbott said.
He also urged the leaders to use first names in addressing each other, "because whatever disagreements we might have, I think it helps if there can at least be personal warmth amongst us".
Yet the Australian leader himself came into the summit locked in an icy war of words with Russian President Vladimir Putin about the downing of a Malaysia Airlines passenger jet over Ukraine in July.
In Brisbane, UN Secretary General Ban Ki-moon echoed former Soviet Union leader Mikhail Gorbachev's fears that tensions between Russia and the West had brought the world to the brink of a new Cold War, and urged the G20 to take the issue on.
- Putin in the hot seat -
Putin faced scrutiny on Friday after the prime ministers of Britain and Australia accused him of being a bully and harbouring imperialist ambitions in the context of the Ukraine separatist crisis.
Despite the standoff, Abbott and Putin found time to smile for the cameras as they exchanged a warm handshake ahead of the closed door talks.
Moscow hit back at the criticism with strong language against the West that included a warning for France against further delay in handing over a warship promised under a 2011 contract, as Putin and French President Francois Hollande prepared to hold bilateral talks Saturday evening in Brisbane.
Interviewed by the TASS news agency, the Russian strongman said his sanctions-hit government was prepared to deal with a potentially "catastrophic" fall in oil prices.
Their decline to four-year lows is a boon for growth in other G20 countries but threatens to explode Russia's deficit and is already depressing the ruble, as the economy struggles to fend off the effects of Western sanctions.
Putin assailed other G20 countries for imposing the sanctions over Ukraine and the Malaysia Airlines plane incident.
But he said he would not raise the topic of sanctions at the G20. "Why should I draw attention to this, ask for something? It's pointless."
One point of the Brisbane summit is to flesh out the G20's commitment of lifting economic growth by up to two trillion dollars in the next five years through policy reforms.
A draft copy of the "Brisbane Action Plan" to be adopted Sunday said that, owing to worries about sluggish conditions worldwide, the leaders will agree to reforms that could accelerate growth by 2.1 percent, up from a previous target of 2.0 percent.
The leaders are also striving to close corporate loopholes that allow some multinational companies to pay a pittance in tax depending on where they are domiciled, after a major dispute erupted over Luxembourg's beneficial tax deals with a slew of companies.
The prime minister of Luxembourg at the time was Jean-Claude Juncker, who is now the head of the European Union's executive commission.  
In Brisbane on Saturday Juncker defended his position over the sweetheart deals, and endorsed a global fight against tax evasion in the works from the G20.