The coalition expects 490,000 public sector jobs to be lost by 2014-15 as a direct result of its drastic spending cuts, Danny Alexander, the chief secretary to the Treasury, has accidently disclosed.

Alexander inadvertently allowed two pages of tomorrow's spending review to be photographed as he left the Treasury building.

It is the first time the government has stated that job losses of this order are going to happen due to the spending cuts.

The document also proposes that public sector employers should try to strike deals to cut hours to reduce the level of redundancies.

The forecast is based on the estimate of the Office of Budget Responsibility, the new independent body set up by the coalition to publish independent forecasts on jobs, growth and borrowing.

The two pages also set out plans for extra spending on climate change, but also hold out the possibility of an as yet unspecified energy tax.

David Cameron was also photographed today with the first page of his defence statement to the Commons this afternoon. In it he claims defence cuts will be in the order of 8%.

The Alexander document warns the spending cuts "inevitably impact" on workers because the pay bill in Whitehall accounts for around half of all departmental spending. It also claims the overall public sector pay package has been generous, with pay packages four times as high as those in the private sector.

Action on pay – a two-year freeze for all but the lowest paid is already in place – will help reduce job losses, the papers say.

Each public sector employer will have to "determine the workforce implications of spending settlements", the document says.

It adds: "Government will do everything they can to mitigate the impact of redundancies." This will be done by creating conditions for private sector growth, encouraging pay restraint and reduced hours and supporting employees facing redundancy so they can find work in the private sector.

The government hopes that the private sector will keep its promise to take up the slack in the labour market caused by the large shedding of public sector jobs.

The document also states that the OBR will produce a new forecast on 25 November, but does not expect that forecast to change the overall picture on job cuts.

The paper pledges that the UK will contribute £2.9bn in international climate finance and sets out plans to focus on developing wind power to help reach environmental goals.

The last sentence in the page held by Alexander appears to be a commitment to increase environmental spending – by 30% in this draft, although the brackets suggest last-minute negotiations or calculations. A footnote suggests this includes money raised by levies on bills, such as the Renewable Obligations scheme and, potentially, new funds, increases in the climate change levy, for example.

"That makes it sound like there might be more expenditure, but I don't think that's what's going on," said Matthew Lockwood, associate director at the IPPR thinktank.

The first section includes an on-message pledge to "improve efficiency" of policies to support renewable energy, but this does not guarantee funding cuts or stability, or reveal which will be the favoured technologies. However, wind turbines are given a specific name check (directly and indirectly as that is the main reason for investing in ports), backing expectations that some funds, including those for feed-in tariffs for home and other small renewable energy, and some "solutions", like tidal barrages, will be reduced or even dropped altogether.

The only specific mention of the wider environmental agenda is "maintaining current coverage" of subsidies to farm in more eco-friendly ways, but this does not specifically include a commitment to maintain the smaller but more effective "higher level" payments, rather than simply the big, but relatively ineffective "entry level" scheme.

The middle part of the page is spent repeating the UK's pledge to put £500m a year (totally £2.9bn from the pledge in 2009-10 until the end of the spending review period in 2015) into an international kitty to fund carbon reductions and adaptation in other parts of the world. As the Guardian suggested today this is expected to be paid by the Department for International Development, and will almost certainly come from another previous promise to increase UK development funding to 0.7% of GDP – to the disappointment of both development and environment campaigners.

That section is notable, however, for its rather defensive tone: making the point that "the UK is responsible for only 2% of global emissions". This is true by the narrowest measure, but the Department for Energy and Climate Change itself has admitted that this figure ignores the huge emissions generated by UK consumption. This is likely to be a much bigger proportion, as most recently suggested by a soon-to-be-published report from thinktank Policy Exchange, which found that measured by production the EU's emissions have decreased since 1990, but by consumption the total has increased by more than 40%.

Finally, the bottom third is taken up with repeating existing government announcements, the financial implications of which are at best unclear.

Alexander's gaffe is probably the worst of many recent cases of papers carried by leading politicians being photographed leading to embarrassing disclosures.

During the coalition negotiations Nick Clegg's "red lines" were photographed, and in 2008 the then-housing minister Caroline Flint was photographed carrying a paper with predictions of a major fall in house prices.