The word "historic", already being used to describe the just-accepted Paris climate agreement, is more than warranted. The world will now have a new and comprehensive regime in place to shape how its diverse nations go about the urgent task of reducing their greenhouse gas emissions.
That's why climate activists are ecstatic the world over right now. It's a big deal.
The more ambiguous news, however, is that this document, by its very nature, depends on key sectors of society to respond to help make sure its goals are realised. Countries, companies and individuals all across the planet will have to do the right things - and very hard things, at that. And it's too soon to tell exactly how they will do so.
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What's more, even if everyone plays by the rules, the standards and goals set out by the Paris agreement may not be enough to prevent the catastrophic effects of climate change. New science suggests that forces already set in motion - the melting of glaciers, the release of carbon dioxide from thawing permafrost - could unleash considerable impacts that this new deal is unable to prevent.
But those doubts should not overshadow the magnitude of what was accomplished. And there are reasons for hope.
The energy sector
Most important is the energy sector. We have seen even before this landmark text a sharp growth in renewable energy instalments around the world, from the US to Germany to China. We have seen the coal industry begin to stumble and a surge in natural gas.
The trends, in other words, are already pointing in the direction that the agreement itself means to encourage.
See this AP interactive on our warming world :
But what will energy companies - and energy investors - do once they read that the world now intends to "reach global peaking of greenhouse gas emissions as soon as possible . . . and to undertake rapid reductions thereafter?" Will this send a strong enough "signal", in the words of US Secretary of State John Kerry, to change the decisions that these companies, and these wealthy individuals, make?
The private sector
An evolution in the private sector is crucial, because despite all the powerful language of the Paris agreement, it does not immediately oblige countries to do anything more than what is contained in their already released climate pledges, or "Intended Nationally Determined Contributions".
And - as has been often stated - these pledges are not compatible with the Paris agreement's ambitious temperature target, which is to limit "the increase in the global average temperature to well below 2C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5C above pre-industrial levels."
The document requires countries whose current pledges go out to 2025 to update them (and up their ambition) in 2020, and countries whose pledges go out to 2030 to do the same. So a lot of progress needs to happen between now and 2020, in the form of rapid installations of wind, solar and other forms of renewable energy around the world. If in 2020 countries look around and see that they're in the midst of a surprisingly rapid clean energy transition, then it will be easy for them to strengthen their pledges.
The future of fossil fuels
Until now, analysts have generally expected the clean energy transition to be gradual rather than radical, and that we will still be significantly dependent upon the use of fossil fuels for some time. One key measure of the success of Paris is how much it changes this dynamic. And early signs suggest that it could.
The new text sends "a very strong signal to business and investors that there is only one future direction of travel to reduce emissions in line with a 1.5 degree pathway," said Stephanie Pfeifer, chief executive of IIGCC, a network of 120 institutional investors with over 13 trillion euros in assets under management, in a statement in response to the new document. "Investors across Europe will now have the confidence to do much more to address the risks arising from high carbon assets and to seek opportunities linked to the low carbon transition already transforming the world's energy system and infrastructure."
Another key question, meanwhile, is what the agreement will do to spur more research into a suite of technologies that go unmentioned in the text, but nonetheless are effectively put in the hot seat by it - so-called "negative emissions" technologies that would be able to remove carbon dioxide from the air.
Scientists have said that the aspirational temperature goal contained in the text, namely that "parties should pursue efforts to limit the temperature increase to 1.5C above pre-industrial levels", likely won't be possible unless we have a large-scale way of removing carbon dioxide from the air. Many scenarios for limiting warming to 2C also rely on such technologies.
The new text itself appears to empower these technologies further when it says that the ultimate goal is to "achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century". Sources are things like coal-burning power plants - sinks are things like trees, forests and oceans. But the language in this section may also subtly invoke negative emissions technologies.
Commenting on this "long term goal" language, John Schellnhuber, director of the Potsdam Institute for Climate Impact Research, remarked that "to stabilise our climate, CO2 emissions have to peak well before 2030 and should be eliminated as soon as possible after 2050. Technologies such as bio-energy and carbon capture and storage as well as afforestation can play a role to compensate for residual emissions, but cutting CO2 is key."
In other words, yes - there is going to be a lot of carbon cutting in coming centuries, but there may also have to be quite a lot of carbon withdrawal and burial by human-made devices (or carbon sequestration by human-planted trees). The conversation needs to start now about these technologies - many of which have major side-effects, such as the use of very large amounts of land (to grow the crops and plants that would be burned in bioenergy combined with carbon capture and storage schemes).
"So far, negative emissions are basically 'science fiction,'" says Oliver Geden, a scholar with the German Institute for International and Security Affairs. "We will need a serious debate on the consequences, and R&D on a massive scale."
The Paris accord thus does indeed deliver us into a very new world. Even as we monitor ongoing changes in the climate, our attention must now shift to the business and technology trends that just may save it.