The Paris climate deal has been hailed as the beginning of a low-carbon era and widely greeted as a turning point - albeit only a first step in the right direction on a difficult road ahead.
- The achievement: A comprehensive global treaty to combat climate change, signed by 195 developed and developing countries and emerging economies and committing all nations to cutting greenhouse gas emissions.
- The timeframe: To follow from the Kyoto Protocol when it ends in 2020 and will enter into force once it is ratified by at least 55 countries which cover at least 55 percent of global greenhouse gas emissions.
- The goal: The Paris agreement reiterates that warming should stay well below 2°C. The Paris deal is binding and has raised the bar by adding an aspirational goal of "pursuing efforts to limit the temperature increase to 1.5°" above pre-industrial levels.
- The pathway: The deal calls for global emissions to peak "as soon as possible" and for a balance between the rate of emissions and the rate of removal (by vegetation or carbon capture and storage for example) to be achieved sometime between 2050 and 2100.
- The work ahead: 185 countries submitted pledges in the lead-up to Paris, covering 94 percent of global emissions and 97 percent of the world's population. The deal commits countries to review their pledges every five years, with an expectation commitments will be raised each time.
- The finance: Developed countries will need to move from fossil fuel energy to renewable sources quickly. The challenge is bigger for developing countries, and wealthy economies have agreed to provide a climate fund worth $US100 billion a year after 2020.
Professor Martin Manning, from the Climate Change Research Institute at Victoria University, said the global nature of the Paris deal had made it possible for countries to aim for a more ambitious target.
"While governments still do not have detailed plans for reducing greenhouse gas emissions fast enough to keep to the 2°C, they have now made a much higher commitment for achieving that. This is the result of a more collective approach to a global problem."
The below 2° target implies a goal of net 0° CO2 emissions (a balance between the amount of carbon emitted into the atmosphere and the amount taken up by trees) during this century.
Climate Change Research Institute director Professor Dave Frame said that was "probably the best that we could realistically hope for".
"Major fossil fuel economies couldn't cope with a clear statement of a net 0° CO2 target at this stage. But the direction of travel is clear."
The deal makes no mention of actual targets for emissions reductions, though, and Victoria University climate scientist Professor James Renwick said there was no time to lose if the world was serious about 1.5°.
"Global emissions would need to start coming down significantly in the next year or two.
"Governments need to come up with strategies over the coming six months to a year that will put us on a path to 0° net global emissions within the next 50 years at the latest.
"For New Zealand, as a developed nation that should be leading the way, we need a national-level strategy in 2016, one that will see our actual emissions reduce, rather than us buying our way out with carbon credits."
Climate change not going away
However, even if all this were to happen, climate change is not going to go away any time soon.
The Paris agreement is in line with the best-case scenario in the most recent report of the Intergovernmental Panel on Climate Change (IPCC), which was published late in 2013.
At the time, the IPCC stressed that this scenario, known as RCP2.6, was the only one in which global temperatures peak between 1.5° and 2° and begin to decline again within this century. Even then, the impacts of climate change will be noticeable.
The world has already warmed by 1°. A warmer atmosphere holds more water and has a greater potential to dump torrential rainfalls.
Warm water takes more space
Oceans have taken up more than 90 percent of warming; as they warm up they expand, because warmer water takes up more space. As a result, the sea level has gone up 19cm.
These processes will continue but, as a result of the Paris agreement, future impacts will be at the lower end of projections. For sea level rise, this means between 30cm and 60cm by the end of the century.
Antarctic Research Centre director Tim Naish said a 2°C limit to warming would keep climate impacts at a "guard-rail, below which risks are considerably reduced".
"This is particularly true with respect to components of Earth's climate system that might have global and irreversible consequences, such as the melting of the polar ice sheets."
Ralph Sims, the director of the Centre for Energy Research at Massey University, travelled straight from the Paris meeting to an Asia Pacific Economic Cooperation forum on fossil fuel subsidy reform.
He said one of the most important aspects of the Paris deal was it would require actual reductions in emissions rather than "relying on buying carbon credits offshore as is the current intention".
But Paris would perhaps be remembered most for what happened outside the plenary sessions, the "momentum of businesses, cities, NGOs (non-government organisations), financiers, bankers, indeed across all civil society, in their intent to move towards a rapid transformation to a low-carbon economy", he said.
While the Paris agreement lays a foundation for stronger climate action in the future, the work is only just beginning.
* Veronika Meduna is a producer for RNZ's Our Changing World science show and author of the book Towards A Warmer World: What Climate Change Will Mean For New Zealand's Future.