Yesterday's joint announcement by the US and China on post-2020 emissions reduction goals marked a watershed in global climate diplomacy. The symbolism of the world's two largest economies and emitters committing together to constrain emissions marks a significant departure from the antagonistic posture the two countries had towards each other in advance of, and at, the Copenhagen climate summit five years ago.

In some respects the announcement should not be a surprise. The US and China have been talking quietly for around a year on their respective post-2020 targets. Both nations have implemented domestic policies to tackle air pollution, boost clean energy investments, and meet their existing 2020 emission targets.

China's early indication of what it is prepared to contribute will in part be driven by the desire to avoid the diplomatic flak it received in Copenhagen. Early communication gives countries time to justify their positions and shape the parameters of the final outcome.

The EU also announced its initial post-2020 offer in October — at least 40% reductions on 1990 levels by 2030.

Combined, countries that now account for half of global emissions have signaled their initial and broad-brush commitments for post-2020. These will eventually be captured as part of the climate change framework to be agreed in Paris at the end of next year.

All of these commitments are backed by domestic action. The EU's emission trading scheme ensures it can meet any target it sets. China's efforts to control air pollution, boost energy security and enhance its international stature are all driving the development of carbon pricing, regulations and incentives that will slow and ultimately cap emissions.

Mainstream investors and experts suggest China's coal consumption will peak well in advance of its national emissions. President Obama is using his executive authority, regardless of Congress, to implement emission standards for vehicles, power, oil and gas.

All face domestic political challenges in achieving their targets. Yet all of these countries can and should commit to stronger action.

The next milestone will be when these and other major emitters formally communicate to the UN their overarching offers — and the more concrete numbers underpinning them — early in the new year. 

At the next UNFCCC meeting in Lima, Peru next month, countries will seek to define the information underpinning their post-2020 targets. For example, we currently don't know at what level China plans to peak its emissions and this will need to be clarified.

Again, this is a significant departure from the dynamic before Copenhagen, where many countries held back on making commitments until just before the meeting. There is now a strong push from many nations to ensure that targets are transparent, that the assumptions behind them are understood, and that the collective action adds up to avoiding a 2°C increase in global temperature above pre-industrial levels (the internationally agreed benchmark of country and global actions).

The other departure from previous international climate change frameworks like the Kyoto Protocol and the post-Copenhagen Cancun Agreements is that countries are now seeking to establish a system of ever-increasing emissions reduction ambitions. This 'cycle of contributions' would see countries advance initial offers for international scrutiny, with final contributions attached to the agreement. Progress on targets would be reviewed. Timed to coincide with the major scientific reports, this cycle would start again, and again, and again.

Underpinning this would be a 'no backsliding' principle, so each new commitment is at least as ambitious as the previous one.

There does appear to be a growing awareness in the Australian Government of these new international realities. Strong commitments from the Environment Minister that Australia will advance a post-2020 target in the first half of next year is a good step. So too was the Treasurer's acknowledgement of the export opportunities for clean energy in the region, as China and others continue to decarbonise their energy systems. The Foreign Minister is hoping to attend the next round of negotiations in Lima, and this is an opportunity for Australia to announce a transparent domestic process to define its post-2020 contributions next year.

Ultimately, however, these actions need to be backed by a credible domestic policy framework that decarbonises the economy over time. This will require firm limits on major emitting sectors, access to international carbon markets, a strong and growing renewable energy sector, and regulatory measures to permanently close old and inefficient coal-fired generation. This is an awfully long way from the Government's current position, but ultimately it is where it will need to be if it is going to respond to the changing international environment.