The answer, sadly, seems to be 'very little'
Ctrl C; Ctrl V. Each autumn, the temptation to cut and paste Budget analysis from previous years becomes harder to resist. There are only so many times you can speculate about the prospects for a 'green Budget', just to see those hopes disappointed by the Treasury's crushingly predictable short termism. Groundhog Day has nothing on British Chancellors.
Sure, the details may vary from year to year. One year questions may centre on will this energy efficiency scheme survive or will that carbon tax be axed? The next, focus will have shifted to levels of green infrastructure funding or budget settlements for clean energy auctions.
This time out the specific policy questions that await an answer include whether the Chancellor will try and compensate for freezing fuel duty, up road-building budgets, and cut electric vehicle grants by improving tax breaks for cleaner vehicles? (Answer: possibly) Will he increase the Climate Change Levy for corporate energy users? (Answer: it looks that way) Will he try and appease the Hard Brexiteers by axing the carbon price floor? (Answer: almost certainly not, but if Brexit goes badly he could yet be tempted) And will he confirm new plastic taxes? (Answer: possibly, but don't expect much detail).
And yet, even if Philip Hammond provides answers to these questions and a few of the other inquiries in the government's bulging green in-tray - can anyone explain why fracking gets fast-tracked and onshore wind gets blocked? Where on Earth is the UK's CCS and nuclear strategy? Why is he reportedly trying to water down the remit of the post-Brexit Green Watchdog? When will Ministers properly explain how they are going to meet their medium-term carbon targets, let alone prospective net zero emission goals? - the chances of him stitching together a genuinely green budget are slimmer than Theresa May's chances of fighting the next election.
The reason for this is simple: there has never been a genuinely green budget. In the 30 plus years since Margaret Thatcher warned climate change could prove to be a planetary crisis, the 20 years since the UK signed the Kyoto Protocol, the 10 years since Parliament passed the world's first Climate Change Act, and the three years since the Paris Agreement was brokered, not once has a British Chancellor stood up and delivered a bold green budget that is commensurate to the scale of the challenge and the opportunity that the low carbon transition represents.
There have been times we have got close: when Gordon Brown commissioned the Stern Review and Ed Miliband ushered through the Climate Change Act; when the coalition quietly introduced clean energy auctions, new energy efficiency schemes, and a carbon price floor. But ever since David Cameron allowed leaks about his alleged desire to 'get rid of the green crap' to stand unchallenged environmental issues have had to content themselves with a line or two (if they are lucky enpough to be mentioned at all) when it comes to British politics annual economic set-piece.
The annual optimistic suggestion that this year will be the year that the Treasury connects the dots between the need to stimulate a sluggish economy, the need to appeal to younger voters, and the need to tackle climate change has always been a triumph of hope over experience.
But this year the failure to make decarbonisation and clean growth absolutely central to the government's economic plans will prove even more disappointing than usual, and not just because the budget comes less than a month after the world's top scientists warned the global economy has just 12 years to virtually halve greenhouse gas emission if it is to avert dangerous and potentially catastrophic levels of climate change.
It is also less than a month since Prime Minister May declared, albeit with caveats, that the government was to call time on the age of austerity. As such the pressure on Hammond is acute to come forward with spending plans that satisfy both that pledge and his own deficit hawk instincts. Various informed previews suggest he will do this by finding some modest extra funding for the NHS and road building, relaxing borrowing constraints on councils that want to build new homes, freezing fuel duty, and offering some new support to the struggling High Street.
This fiscal largesse (although in truth the sums involved will be more cosmetic than seismic) will be undercut by Hammond's grim warnings that his entire plan would have to be ripped up and replaced, most likely with a Singapore-on-Thames low tax model, if a 'no deal' Brexit hits the economy like a runaway freight train early next year. Displaying the political nous for which he is notorious, Hammond's message to the Hard Brexiteers in his party seems to be 'knuckle under and back the government's proposed deal or else we'll give you exactly the kind of tax cutting, deregulatory shock therapy you've been dreaming of since the first time you sweatily flicked through the pages of Ayn Rand'.
However, what is notable by its absence from the speculation about how the 'end of austerity' will be put into practice is any indication that it will mean an end to environmental austerity.
The government would no doubt argue the reason for this is that the green agenda has never been subject to austerity. 'Look,' they say, 'the UK is cutting emissions faster than any other OECD country. We've recently approved over half a billion quid for new clean energy contracts, we're cracking down on plastic waste, we've got a world-leading offshore wind industry, the railways are undergoing their biggest investment programme since the Victorian era, and clean tech R&D spend is higher than ever.'
These are all fair and reasonable points. Except the green economy has been in no way immune from austerity economics. Energy efficiency funding has been cut drastically, green levies have been politicised and curbed (even as the cheaper forms of clean energy have been locked out of government funding), Defra and BEIS were subject to swingeing personnel cuts, CCS funding was unceremoniously culled, the UK's recycling infrastructure is struggling badly following decades of underinvestment. Some favoured green areas may have been relatively well served since 2010, but many others have faced the same ideologically-imposed fiscal headwinds as the rest of the economy.
Moreover, even if the government boasts a reasonably strong environmental track record, the bar for climate action is not set by what previous administrations have done or what other countries are doing. It is set by what scientists recommend is required to avoid dangerous levels of climate change. It is set by global technology trends in favour of cleaner, healthier, and more competitive infrastructure. The problem is that against these bars the British government keeps coming up short.
The end of austerity should be the perfect opportunity to address this problem.
The public justification for austerity was always predicated on the idea that future generations should not have to foot the bill for our spending beyond our means. This analysis was always nonsensical - as any economics undergraduate should know, national and household budgets are not the same thing and cutting in the midst of a global economic slowdown is a sure-fire recipe for a lost decade or two, just as came to pass. But it was particularly nonsensical for environmental spending, on the grounds those who stand to benefit the most from climate change mitigation and resilience spending are those future generations who would otherwise have to face runaway climate change.
If scientists are even half right about the scale of the climate impacts that could be unleashed in the second half of the century, then footing a small share of the bill for building a resilient net zero emission economy sometime in 2070 is going to seem like a very good deal indeed. Did you hear anyone in the 1990s complaining about the fact we were still repaying war loans to the US?
Consider the environmental areas a Chancellor unconstrained by austerity could choose to focus and the economic, political, and moral rationale for bold action becomes ever clearer. Infrastructure funding for energy efficiency upgrades could take a huge cost effective chunk out of UK emissions, genuinely end fuel poverty, improve health outcomes, stimulate the post-Brexit economy by putting more money in peoples' pockets, and boost energy security. An EV and cycling infrastructure blitz could cut vehicle emissions, slash air pollution, and ensure the UK auto industry not only stays put post-Brexit, but reinvigorates itself around the technology that will shape the century. Fast tracked green farming subsidies, plastic taxes, and an even more ambitious R&D programme centred explicitly on clean tech could boost competitiveness in fast-expanding industries, allow the UK to tap into critical export markets and play a role in ensuring the global low carbon transition scales as quickly as possible.
And there's more. Allowing onshore wind and solar to compete for clean energy contracts would curb energy bills and drive yet more polluting coal off the grid, while accelerating efforts to establish the UK as a smart grid and energy storage hub. Confirming the UK's first Green Sovereign Bond and mandating climate-related risk disclosure would both cement the City's position as a green finance leader and help deflate a carbon bubble that could soon destabilise the entire global economic system. This list of well-established, thoroughly researched, off-the-shelf policy moves is in no way comprehensive.
None of this would cost that much when compared to the Treasury's other spending lines. All of it would offer tangible economic as well as environmental returns. And the vast majority of it would be hugely popular with voters, including those younger demographics the Conservatives urgently need to find a means of reaching (the exception, of course, would be the small cabal of Tory climate and eurosceptics who retain an outsized influence over how the government defines the national interest).
If he was feeling really bold Hammond could even attempt to honestly address some of the great long-term structural challenges decarbonisation presents. He could unequivocally promise that all tax receipts from fracking (which admittedly looks set to be about £5.50 at the current rate of earthquakes) will be earmarked for green heat technology deployment. He could promise to increase Air Passenger Duty to help compensate for the environmental costs of Heathrow expansion and pay for a huge and urgent increase in green aviation R&D. He could order a Royal Commission into how to deliver a 'just transition' for the North Sea, how to generate new tax receipts as fossil fuels are phased out, and how to avert a carbon bubble crisis.
The sad truth is it is easier to imagine Philip Hammond standing up later today and challenging Jacob Rees-Mogg to an arm wrestle to decide whose Brexit strategy to enact than it is to envisage the Chancellor putting forward a coherent and credible green vision. And that tells you all you need to know about the government's current set of priorities. It also tells you why this Budget is likely to prove even more disappointing than usual. Austerity may have ended, yet there is still no end in sight to the government's equally short sighted triangulation on climate change. As a result we are staring down the barrel of plausible that are even worse than another lost decade.