Two decades of summits and resolutions have not stopped mankind pumping growing quantities of greenhouse gases into the atmosphere, despite a wealth of evidence that it is causing more frequent and devastating droughts, storms and floods.
Obama devoted a surprisingly long section of Monday's inauguration speech to climate change -- more than a minute out of about 20. He said failure to respond to the threat "would betray our children and future generations."
"The path towards sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition; we must lead it," he said.
"Great strong words on climate... The U.S. President could not commit stronger to delivering now," Connie Hedegaard, the European Union's climate commissioner, wrote on Twitter.
"We have got work to do on climate change and President Obama was very forthright about the need to tackle climate change," Australian Prime Minister Julia Gillard told reporters.
A succession of recent natural disasters has put a sharper focus on climate change.
Superstorm Sandy struck the United States in October, a typhoon left more than 1,000 people dead or missing in the Philippines in December and this month a searing heatwave caused hundreds of wildfires in Australia.
The United States has declared a natural disaster in its central and southern Wheat Belt because of a severe and persistent drought.
The global economic slowdown has made the governments of richer nations more reluctant to invest in technology to mitigate climate change, led by a shift from fossil fuels towards clean energies such as wind or solar power.
Developing countries whose carbon emissions are rising fastest say they cannot afford the entire cost of shifting to greener technology and that developed nations should help more.
In the latest failure of environmental diplomacy, U.N. climate negotiations in Qatar in December ended without a single new pledge to cut pollution from a major emitter.
Instead, governments agreed to try again for a binding United Nations pact to limit climate change that would enter into force from 2020, replacing the Kyoto protocol adopted in 1997 that the United States never ratified.
Environmental campaigners were dismayed at the decision to wait years before taking concerted action.
Obama's renewed promises could help.
"It really changes the nature, style and substance of the U.S. engagement with the international climate negotiations," said Bill Hare, a scientist who heads Berlin-based Climate Analytics.
He said that Washington, even in Obama's first term, had low ambitions for confronting climate change and that had dimmed efforts by other major emitters. China, the United States, India and Russia are the top greenhouse gas emitters.
Unlike all of Washington's major allies in developed nations, the U.S. Congress has not legislated caps on domestic greenhouse gas emissions.
But Obama can still take the lead with actions that side-step the divided Congress.
The administration could impose tougher rules for coal-fired power plants or introduce measures to promote renewables. It also faces a decision on whether to approve TransCanada Corp's planned $5.3 billion Canada-to-Nebraska Keystone XL oil pipeline.
"Words in an inauguration speech are one thing... Many are waiting to see what specific actions the president will take," said Samantha Smith, head of the WWF conservation group's climate and energy initiative.
She still praised Obama for starting a new U.S. debate about climate change with the speech. She said one measure Obama could take included a phase-out of fossil fuel subsidies.
When Obama first came to office he promised to act on climate change in a shift from ex-President George W. Bush who decided against trying to ratify the U.N.'s Kyoto Protocol for limiting emissions by industrialised nations.
In 2009, Obama promised to cut U.S. greenhouse gas emissions by 17 per cent below 2005 levels by 2020. But the U.S. Senate did not ratify the plan.
Kyoto, originally backed by all other major developed nations, has been hit by defections by Russia, Canada and Japan from January 1 this year, leaving only a core group led by the European Union and Canada targeting deeper cuts by 2020.
Bush and the U.S. Senate reckoned that Kyoto unfairly omitted targets for emerging nations such as China and India and would mean U.S. jobs moved abroad. On the other hand, Washington risks losing a race to develop clean technologies.
A study by the Pew Charitable Trusts last week indicated that worldwide revenue from installing clean energy facilities could total $1.9 trillion from 2012 to 2018.
With the right policies, it said the United States could get 14.5 per cent of the total.