31 October 2014 Last updated at 16:09

IPCC keen to avoid the ghost of 'Hopenhagen'

IPCC scientists and government officials meeting here in Copenhagen are likely to work late into the night to deal with some very heavy questions.

And it won't just be queries about the "severe, pervasive and irreversible impacts" of climate change.

In those quiet corners they will huddle to answer philosophical challenges such as "How long is ever?" - posed by the US in a response to one part of the Synthesis draft report.

One or two are likely to look over their shoulders this chilly Halloween, and keep an eye out for the spooky presence that no delegate dares to name.

Yes - the ghost of "Hopenhagen" still sends shivers through the timbers of the most seasoned IPCC'er.

Back in 2009, greens and others went blue from the cold as they queued to get into the not-very Bella centre, site of the UN talks that were meant to deliver a new global deal.

Being frozen out was an apt metaphor for what was to come.

Copenhagen, or Hopenhagen as it was cloyingly dubbed, was a meeting that was meant to "save the planet".

It ended in farce and failure.

Now, the IPCC is separate from the UN's internal climate process - but the ghosts of 2009 still echo here.

Downhill all the way

The Danish government is very keen to show the world that things have really changed over the past 5 years.

They have been organising tours of some of the country's greenest facilities, to emphasise once again, that they are still the "good guys", despite the failings of 2009.

There's no clang of cowbells just yet on a giant building site some four kilometres from the heart of Copenhagen.

However, in two years time skiers will be swishing their way around the rooftop of this new facility that's starting to emerge on the water's edge near the Danish capital.

The Amager Bakke project will see the construction of a massive waste to energy plant that will tower over most other buildings in the city.

As well as producing 60MW of electricity entirely from old rubbish, the facility has been designed to incorporate an artificial ski slope on the roof.

Looking down on the emerging structure, managing director Ulla Rottger is buzzing with enthusiasm for the project, which is costing around 500 million euros.

It will replace the current plant that dates from the 1970s.

"The neighbours see that as a positive," she says, pointing to apartments just 250 metres from the site.

"There will be no noise and no smell from the garbage. We are just 4km from the mayor's office but, yes, it's possible to treat waste in an environmentally friendly way in the middle of the city."

But not everyone is convinced of Denmark's green sheen.

WWF International produced a report in recent weeks that measured the ecological footprint of countries.

Denmark finished fourth on the list of shame, just behind environmental outliers such as Kuwait, Qatar and the United Arab Emirates.

If everyone on the planet lived like a Dane, the report said, then we'd need 4.5 Earth-like planets to sustain us.

The problem is they grow a lot of crops here, often to feed the pig industry, and there is little in the way of untouched natural space. So their footprint per capita is high by these measures.

Back at Amager Bakke, there are plans to install a chimney that will emit a symbolic, environmentally friendly smoke ring for every tonne of carbon dioxide that's emitted.

Is this just Danish greenwash?

Yes, says writer and journalist Michael Booth, who has covered the country extensively.

"We have the highest energy costs in Europe, the majority of those costs are taxes imposed by the government," he says.

"So I get kind of annoyed by Danish politicians swanning around the world preaching about how green Denmark is. I think it is rank hypocrisy."

Questions of taxes and hypocrisy are not for the IPCC - their job is to outline the parameters of the climate problem and how it might be tackled, globally.

The process requires complete consensus. Over 190 governments have to agree and so do the scientists.

Hence the late nights, and ghostly huddles.

The problem is that because of that consensus, everyone goes home believing the report supports their own interpretation of how to tackle climate change.

If we are backed up by the science, they think, why should we compromise?

That's partly why Copenhagen 2009 came a cropper.

It is no wonder that some accuse the poor old IPCC of finding refuge in discombobulation.

How long is ever? How soon is now...

Follow Matt on Twitter @mattmcgrathbbc.