The world's nations on Sunday set their sights on a new all-encompassing pact on climate change that marks a break with the past and will also be gruelling to achieve.
The so-called Durban Package will, for the first time, bring all greenhouse-gas users into a common legal regime under the UN flag, in the aim of cranking the carbon combat into higher gear.
This goal dates back a decade and, ironically, is rooted in the argument of former US president George W. Bush, a bogeyman to many in the green movement.
To activists' fury, Bush in 2001 declared the United States would never ratify the Kyoto Protocol, the cornerstone treaty of the UN Framework Convention on Climate Change (UNFCCC).
He said Kyoto was unfair as its format clamped legally binding emissions constraints only on rich countries, not poor ones, which instead were deemed to be historic victims of global warming.
Today, Bush's rationale has prevailed.
Voraciously burning coal to power its surging economic growth, China has now become the world's No. 1 greenhouse gas emitter.
Joining it in the top ranks are India, Brazil and Indonesia, all racing out of poverty.
As a result, carbon emissions are now setting the world on course for possibly four degrees Celsius (7.2 degrees Fahrenheit), twice the 2 C (3.6 F) goal enshrined by UNFCCC parties last year as a safe maximum.
Rich countries that were leading emitters back in 1997 -- when the Kyoto Protocol was signed as a framework accord -- are now the minority emitters.
This is what makes the Durban deal special.
The broad agreement reached at the marathon talks under the UNFCCC takes a hammer to the north-versus-south paradigm.
If all goes well, a new accord will be wrapped up in 2015 and take effect in 2020, placing rich and poor under common legal constraints.
That is the goal, but reaching it will be arduous.
As was shown in Durban, where a 12-day conference was extended by two days and nearly collapsed in bickering, the power players in climate politics will defend their interests vigorously.
This will especially be the case if the crisis that has overwhelmed much of the world's economy is prolonged.
Coal, oil and gas are the backbone of the energy supplies today. Improving energy efficiency and switching to cleaner, renewable sources carries a cost that belt-tightening governments may resist.
Also destined to haunt the 2015 negotiations are fundamental questions of who, what and how.
"Negotiating the details will be extremely tough," said Elliot Diringer of the Center for Climate and Energy Solutions, a Washington think-tank.
Top of the list is defining the status of the accord, whose legal profile was left deliberately blurred in Durban.
It must satisfy the European Union, which in contrast to its chaos back home wielded its clout in Durban to great effect, seeking tougher legal controls over polluters.
It must also meet the position of the United States, where conservative Republicans in Congress and a verbal lobby of climate sceptics make any chance of ratifying a treaty with tough constraints remote indeed.
And it must also reassure developing countries that they will not carry the can for warming which is the historical responsibility of rich economies that were the first to benefit from fossil fuels.
Meanwhile, there is a host of side issues that could easily flare up and disturb these very delicate negotiations.
They include how to fill the Green Climate Fund, a mechanism launched in Durban that, in principle, will help channel up to 100 billion dollars a year by 2020 to poor countries facing worsening floods, drought, storms and rising seas.
"We cannot allow the Green Climate Fund to wither on the vine," said Celine Charveriat of Oxfam.
"Governments must identify significant and predictable sources of money for the Fund without delay, such as a tiny tax on financial transactions and a fee on emissions from international shipping."
In the coming years, the sound of the advancing juggernaut will become ever louder. To reach the UN's 2 C (3.6 F) target, emissions which are currently rocketing skyward must fall by 8.5 percent annually by 2020 compared with 2010 and then continue to retreat each year, according to two newly published studies.
"The impacts of climate change are ever more evident and we pump ever more carbon pollution into the atmosphere each year," warned Alden Meyer, director of strategy and policy at the Union of Concerned Scientists (UCS).
"We are in grave danger of locking in temperature increases well above two degrees Celsius, which would foreclose our ability to avoid the worst impacts of climate change."
Explore further: New report highlights 'significant and increasing' risks from extreme weather