It seems now that the only way Australian prime minister Tony Abbott can justify his current suite of climate policies – or the lack of them – is to repeat those words that he famously uttered just a few years ago: climate science is crap.

Because if the climate science is not crap, then it is becoming increasingly apparent that Abbott’s policies are.

The announcement of a climate pact by the US and China on Thursday shows that the world, and more particularly the two biggest economies and polluters, are serious about the science, and are serious about doing something about it.

It is a game changing announcement that is designed to force other countries to act. China, for the first time, has agreed to cap emissions before 2030. It will likely do so well before that. The US has upped its target to 26-28 per cent by 2030.

What they announced is not yet quite enough to ensure that the world does not breach its stated target of limiting average global warming to 2°C, but it is a significant down-payment designed to build momentum to a Paris agreement. The details, and possibly the ambition, will be worked out in the coming 12 months. But it serves to warn outliers – read Australia, Canada, Russia, OPEC – that they cannot use a China-US standoff as the cover from which to throw rocks through the windows of climate negotiations.

“As the world’s two largest economies, energy consumers and emitters of greenhouse gases, we have a special responsibility to lead the global effort against climate change,” Obama said on Wednesday in a joint news conference with Xi Jinping.

“We hope to encourage all major economies to be ambitious – all countries, developing and developed – to work across some of the old divides, so we can conclude a strong global climate agreement next year,” Obama said.

That includes Australia.

And the timing is quite deliberate. It is impossible to underestimate the dismay expressed in the major economies about Australia’s refusal to include climate change on the agenda for the G20.

By making this announcement just days before the G20 meeting in Brisbane, Obama and Xi have chosen deliberately to thrust it on centre stage.

Abbott, to use one of his own phrases, has been “shirt-fronted” by the two most powerful leaders in the world on the issue of climate. And just to add to the atmospherics, Brisbane – like the rest of the east coast – will be caught in the grip of a heat wave, with temperatures forecast to be nearly 10°C above the November average on Saturday and Sunday.

The problem for Abbott is that his government no longer has the tools to make any such commitment.

Abbott has dumped the carbon price to satisfy an election slogan, but his rhetoric against carbon pricing has become even more extreme, even in government. Direct Action will struggle to reach even the modest 5 per cent reduction target by 2020, let alone the 19 per cent target recommended by the Climate Change Authority, even before this announcement, or the 30 per cent by 2025 target that The Climate Institute says the China-US deal demands. TCI’s Erwin Jackson said if Direct Action and the emissions reduction fund were used to meet that target, it would cost around $30 billion a year.

Meanwhile, Abbott’s move to slash the renewable energy target goes against the international trend to accelerate the deployment of wind and solar and other renewables. And his attempt to curb climate science, research, advice, and clean energy funding goes against everything that the world is doing, and the findings of the IPCC just over a week ago.

This puts enormous pressure on Abbott and his government. He can either back-flip on climate policy or throw in his lot with the climate deniers that dominate the Republican Party – where the head of the science committee is more interested in aliens than climate change – and his “best buddy” Steve Harper, the Canadian prime minister.

US Senate leader Mitch McConnell describes climate policies and the like as a “war on coal”. Abbott is inclined to agree and, like the Republicans, has surrounded himself with ultra-conservatives and climate denying advisors and is equally determined to extract as much coal as he can “for the good of humanity.”

But here’s the problem, the world is no longer so interested in Australia’s coal. The price has fallen dramatically, and China has already slashed coal imports by half in recent months and may end them entirely within a few years, according to some analysts. Even India’s energy and coal minister said this week that it may end imports of coal within three years.

So, what’s Plan B for Abbott? Well, there isn’t one.

The response by the Abbott government to the China-US climate pact was revealing. Here it is in full, a desultory 103 words:

“We welcome the announcement by the United States and China to reduce or cap emissions. “The Government is already delivering on Australia’s commitment to reduce emissions by 5 per cent on 2000 levels by 2020. We have always said that we will consider Australia’s post-2020 emissions reduction targets in the lead up to next year’s Paris conference. This will take into account action taken by our major trading partners. In the meantime, what’s important for Australia is that we have replaced Labor’s ineffective and costly carbon tax with a policy that will actually deliver significant emissions reductions.”

Well, not quite. It has just dumped a policy that actually did achieve significant reductions, which have been dramatically reversed since the carbon price was dumped in early July and the amount of coal burned for electricity jumped sharply.

As Ross Garnaut told The Guardian, the US-China deal leaves Australia’s climate policy exactly where it was before the announcement – “up shit creek”. The Guardian’s Lenore Taylor added that Australia did not even have a paddle. But the Coalition will likely go into the next election – where climate change and clean energy policy will again be a major theme after success in Paris – without even a canoe.