It's been nine years since a gathering of environment ministers in the Swedish city of Malmo declared that the world urgently needed to reform the way it governed itself environmentally.
Change was needed, they said, including a "greatly strengthened institutional structure for international environmental governance... that has the capacity to effectively address wide-ranging environmental threats in a globalising world".
In other words; the existing structures and mechanisms weren't effective for an age that was finding an ever increasing number of environmental problems at its door, and realising just how interlinked those problems were with human progress.
The UN Environment Programme (UNEP) didn't have the clout, it was said; responsibility was fragmented across international institutions, and the growing mountain of environmental treaties generally lacked teeth.
The ensuing years have seen various initiatives that would either reform the system or tear it up and start again. But even though many governments cite global environmental decline as a present and future disaster, there's been little progress on reforming the international bodies intended to lead the global response.
So you might think that as the issue raised its head again last week at UNEP's governing council meeting in Nairobi, the overwhelming emotion would be frustration.
And clearly there was frustration that despite nine years of talks and some constructive ideas, virtually nothing has changed.
But there was optimism too. And having spoken to some of the people at last week's meeting, much of it appears to have stemmed from just one word: Obama.
And the single biggest factor in getting that agreement was that the US, which had consistently opposed a binding treaty under George W Bush, gave its blessing.
The US volte-face thrust other reluctant countries such as China, India and Canada into the spotlight; and in the end, they all put their names to the deal.
This has some in the environment field hoping that the US transition will have the same impact on UN climate negotiations which reach a crucial stage at the end of the year in Copenhagen.
But perhaps more significant in the long term is the new US willingness to talk about reform of global environmental governance.
That appears to have given some other governments fresh enthusiasm for tackling the issue once more.
South Africa's environment minister Marthinus van Schalkwyk noted that his officials had told him there was no point in talking about reform, warning that "everyone will simply restate entrenched national positions, nothing too controversial, lots of code language, basically what they have been saying for nine years. It will be 'political theatre', Minister."
But, he said, he'd decided to prove them wrong, and had been encouraged that other ministers had offered "frank and constructive interventions" during the Nairobi talks.
So what happens now? Well, the UNEP meeting set up a consultation process intended to produce some kind of reform package by 2012.
Many countries, especially in the developing world, are keen to stage another major environment conference then - it will mark 20 years since the Rio de Janeiro Earth Summit - and although it's not confirmed yet, the summit appears likely to happen.
The 2012 timescale may have symbolic appeal but it does present some practical difficulties.
If the UN climate talks do produce a treaty as complex as many envisage, encompassing emission targets, clean technology transfer, funds for forest preservation with the rights of indigenous peoples assured, money to help poor countries adapt to climate impacts, and so on, it could make decisions on issues that logically ought to feature heavily in the overall environmental governance discussions.
The following year, 2010, is a crucial year for biodiversity, marking the date by which governments are supposed to have restrained the global loss of species.
It's entirely possible that a new set of targets and mechanisms will emerge at the annual UN biodiversity convention talks. But they too would pre-empt the environmental governance discussions focussing on 2012.
All this might seem arcane stuff, pitting one UN process against another. But it matters.
Here's one example. Biofuels were much touted as a partial solution to climate change a few years ago. It was only once people started working out the possible implications for biodiversity, food production, water extraction and so on, and working through the climate impacts of clearing forests to grow fuel crops, that previously enthusiastic governments thought about applying some brakes.
Under a single global environment framework, that sort of problem shouldn't arise. The various issues would be considered in the whole, not in discrete parts, so the left hand would know what the right hand was doing.
So you might think it would be sensible to sort the institutional side of things out first, before complex deals emerge on any particular environmental issue.
For many developing countries, a key aspect of this is building their capacity to deal with difficult issues.
At last week's Nairobi meeting, a South American delegate noted that her government's environment department possessed just eight full-time officials.
More than 500 international environmental agreements now exist; and with many of them highly technical in nature, it's impossible for governments with such small resources to represent their interests in the same detailed, specialised, forensic way that the richer countries do.
So a developing world priority is to rationalise this pile of treaties under one umbrella organisation and provide the technical support they need.
If all this is nine years overdue already you might think a little more urgency is called for - and for some observers, the 2012 target date is so far away as to constitute a feeble response to the scale of environmental degradation.
But at least, the slate has been wiped clean and a new process started that the world's most powerful government appears to endorse.
Can it work? If it can, will the outcome be tinkering, or wholesale reform? If it is reform, will a new body include rules and sanctions, as does the World Trade Organization? How will it link environmental issues to human development?
These are all key questions, and much wrangling lies ahead before any answers emerge; but the mercury deal is being seen in some quarters as an indication that the glacial progress in many environmental issues is about to accelerate.