The election of Joe Biden is unquestionably a positive development from the standpoint of climate change.
But breaking out in a spirited rendition of the Hallelujah Chorus would be premature.
Biden has pledged to rejoin the Paris climate accord and to establish an "enforcement mechanism" to achieve net zero emissions from the United States no later than 2050, based on the principle that emitters must bear the full cost of the pollution they are emitting.
Climate Action Tracker — which tracks governments' climate moves — has hailed this as a potential historic tipping point. Coupled with China's pledge to bring its emissions to net zero by 2060, and commitments by the European Union, Japan and South Korea to do the same by 2050, it would put the Paris Agreement's goal of limiting warming to 1.5C within striking distance, it says.
But only if the pledges are lived up to.
In the case of the US, the elephant in the room is the one which the Republican Party has adopted as its symbol.
The election is likely to result in divided government, reflecting a deeply divided country. More than 70 million Americans contemplated the lethal incompetence and moral squalor of Donald Trump's four years in office and decided: "We don't care. He's our guy".
And while it is possible that the two Republican senators facing run-off elections in Georgia in the New Year might lose, which would result in a Senate spilt 50:50 with the vice-president having the casting vote, that is a slender reed on which to rest hopes for a Green New Deal.
Biden's climate plan reads well. The enforcement mechanism of which it speaks must achieve ambitious reductions in emissions economy-wide, we are told, instead of having a few sectors bear the burden of change. But whether it takes the form of a carbon tax or cap-and-trade, it would be dead on arrival in a Senate in which Mitch McConnell and his ilk call the shots.
The plan also includes a lot of what climate policy jargon calls "complementary measures". They cover a wide range of sectors, including electricity generation, transport, buildings and agriculture.
Some could be addressed by executive orders, where the Federal Government uses regulatory powers it has under existing legislation. The Obama Administration did a lot of that, most of which has been rolled backed by the Trump Administration.
Such exercises of regulatory fiat are subject to challenge in the courts, however, and one of the legacies of Trump's rule has been to populate much of the Federal bench with conservative judges. So progress on that front will not be swift or easy.
Other policies require the expenditure of tax dollars or the use of tax credits and would therefore need to be negotiated as part of the normal tortuous budget process.
The question there would be whether Biden's skills at cross-party horse trading will prevail over partisan obstructionism.
Perhaps the best ground for optimism is the extent to which money talks in American politics, and especially in Republican politics. With each year that passes, the smart money and the serious money will be talking decarbonisation, if only because corporate America knows that politicians cannot amend the laws of nature or repeal the laws of arithmetic.
Turning to the international dimension of climate policy — crucial as a global commons is at stake here — it is a welcome development that the US will rejoin the Paris accord.
So is the call for a worldwide ban on fossil fuel subsidies, something New Zealand has advocated for years.
But for the US, as for other countries, working within multilateral frameworks does not mean abandoning national self-interest.
And dangers lurk in Biden's plan to link climate objectives to trade and other relationships, not least with China.
"We can no longer separate trade policy from our climate objectives," the Biden plan declares.
"As the US takes steps to make domestic polluters bear the full cost of their carbon pollution, the Biden Administration will impose carbon adjustment fees or quotas on carbon-intensive goods from countries that are failing to meet their climate and environmental obligations." The idea is to deal with the free rider problem that faces countries which impose a carbon price on their own emitters, only to lose business to competitors in countries which don't, leaving the planet no better off.
The theoretical remedy is to bolster or defend domestic carbon pricing with some form of border tax adjustment — a carbon tariff on imports, perhaps combined with some form of rebate or tax relief for carbon-intensive exports. It has been advocated not only by some eminent economists, including 27 Nobel prize-winners, but also by French President Emmanuel Macron and EU President Ursula von der Leyen.
The risk is that it becomes a pretext for protectionism.
It is not hard to imagine, for example, that American producers of meat from pigs and chickens, or fake meat for that matter, call for an impost on New Zealand beef and lamb, on the grounds of its embedded methane emissions.
The Biden climate plan also takes a number of swipes at China, not only over subsidising domestic emissions — a case of pot calling out kettle — but also for financing high-carbon projects in other countries through its Belt and Road Initiative.
It talks of offering "with partners" alternative sources of financing to those countries for lower-carbon energy investments. Fair enough.
But it also talks of reforming International Monetary Fund standards so as to "establish rules that take unsustainable climate and debt costs — such as those imposed by self-interested Chinese projects — into account when prioritising who gets paid under international debt forbearance." It all smacks of an intention to make climate change policy a battleground in its geopolitical rivalry with China.
That would be unhelpful but it would be consistent with expectations that Washington will be no less wary of, or hostile to, China under President Biden than it has been under President Trump.
Yet surely combating global warming should be an area where pragmatic co-operation, not contentious competition, prevails in relations between the G2.