A US submission to UN-backed negotiations shows how a scaled-down global climate deal which falls short of a full treaty can be agreed in 2015.
Much will depend on the United States, as the world's second biggest carbon emitter whose present administration will be in place beyond the deadline for agreement on a new deal.
National climate negotiators meet this week in Bonn, Germany, in a process which has lost much steam since a debacle in Copenhagen three years ago when countries could not agree a successor to the Kyoto Protocol.
They are now negotiating targets beyond 2020, probably focused on 2030, intended to avert dangerous climate change.
These are the first talks since countries agreed last December in Doha a rather messy patchwork of limited action before 2020.
The US submission presents a pragmatic approach which appears focused on agreeing moderate carbon reduction targets and avoiding a stand-off with China on how to share the burden of emissions cuts between developed and developing countries.
A rather weak deal such as this may be most problematic for the European Union, whose executive European Commission has in the past used the UN process as a focus for energy policy.
It would remove one lever for pressing more reluctant EU member states - and especially Poland - to agree an ambitious carbon cap which would invigorate the EU's carbon market and help the bloc meet its long-term renewable energy goals.
Countries submitted their views on a new climate agreement in March and April ahead of the Bonn conference.
In a new position, Washington ruled out agreeing national carbon caps according to a formula (for example based on per capita income or emissions) which analysts had supposed was one way to allocate a "top-down" global aggregate carbon emissions reduction target between individual countries.
"An approach that imposes contributions from without is neither realistic nor likely to result in wide participation/implementation," the United States said in its March 11 submission.
"It is hard to imagine agreement on any formula or criteria for imposition of contributions, as this would get into the most controversial issues."
Second, and a related point, it supported a less divisive approach for setting targets, based on governments' inclination and willingness, appearing to try to end a long-run battle with top emitterChina over how to share the burden of carbon cuts.
"We consider that the agreement should provide for Parties to define their own mitigation contributions, taking into account national circumstances, capacity, and other factors that they consider relevant."
"Self-identification of measures would result in self-differentiation consistent with national circumstances, capabilities."
The proposals show that the United States is now firmly committed to a "bottom-up" approach which detractors say will fail to deliver an aggregate emissions reduction target in line with ambition to limit global average temperature rises.
The country almost certainly favours voluntary targets, rather than a formal protocol which a polarised Congress would probably not ratify.
The United States may struggle to meet its present voluntary pledge to cut greenhouse gas emissions by 17 per cent below 2005 levels by 2020, with implications for the 2030 ambition it can offer.
US carbon emissions were down 8.1 per cent in 2011 compared with 2005, according to greenhouse gas data published earlier this month.
The drop is partly a result of a switch from coal to gas following the shale gas boom which has since unfolded, coupled with the financial crisis.
But carbon emissions may now flatten or rise as gas prices stabilise and economic growth sees energy demand return, without more ambitious action to cut carbon emissions, suggested the Washington-based World Resources Institute in a report published in February, "Can The US Get There From Here?".
The WRI is pressing for more ambitious action which it says would allow the United States to meet its 2020 target without the need for additional legislation.
Meanwhile, some non-CO2 greenhouse gas emissions may rise.
Hydrofluorocarbons (HFC) are extremely potent greenhouse gases which are replacing CFCs as refrigerants, as CFCs are phased out in line with targets under the Montreal Protocol to repair the hole in the ozone layer of the Earth's atmosphere.
US HFC emissions have risen 12 percent since 2005, more than any other significant greenhouse gas, the UN data shows.
Phasing out HFCs could be a quick way to help to secure the 2020 target.
The nearest the United States has previously come to proposing a post-2020 emissions target was in failed cap and trade legislation four years ago.
The 2009 American Clean Energy and Security Act failed to reach the Senate, after passing the US House of Representatives.
It had outlined rather ambitious targets for a 42 per cent cut in greenhouse gas emissions in 2030 compared with 2005 levels.
It seems safe to assume that the United States will struggle to offer a similar target in the present UN negotiations.
Any reduction beyond the present 2020 target would require a significant shift in energy policy, as underlined by the Energy Information Administration.
The EIA published its 2040 energy outlook in December when it projected US carbon dioxide emissions would rise over the next three decades, "under the assumption that current laws and regulations remain generally unchanged throughout the projection period".
Any significant change in energy policy would require new congressional climate legislation which appears off the table for now, illustrating why the United States will be looking for voluntary pledges through 2030.
Such an approach will not please environmentalists but may be the most the United States can deliver, while its offer of a ceasefire on how to share the burden of global carbon cuts may represent the best chance for a 2015 deal.
This article was originally published by Reuters. Republished with permission.