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It's possible, with the right kind of lighting, to see the ongoing UN climate negotiations as some kind of sealed-in world where Alice in Wonderland logic holds sway.

In this world, with the right amount of political will and political acuity, decisions are going to be made that will keep temperature changes at the planet's surface from rising more than 2C - or even 1.5C - above pre-industrial times.

The hurdles are huge, it's acknowledged.

But with the correct key for each door and a range of foods to shrink this demand and grow that ambition, the Cheshire cat will end up with a big smile on its face and the post-fossil fuel world will at some point return to normal - whatever that is.

However, projection after projection finds that the actions pledged by governments fall far short of what's required to keep the world below 2C of warming with any great level of confidence.

The latest, from the UN Environment Programme, found 2.5C is likely even if governments do the maximum they have pledged.

If they do the minimum, 5C by the end of this century becomes feasible.

Meanwhile, as others have argued - notably Roger Pielke Jr - political and economic realities make it progressively less likely that countries will make the swift transitions away from fossil fuels that would be required to peak global emissions within the coming decade.
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This, perhaps, is the real world.

And in response to its growing reality, a number of scientists - with some reluctance - have been arguing that attention should be paid now to assessing the implications of the bigger changes that are becoming more and more likely.

I say "with some reluctance" because dipping a toe into these waters can imply an acceptance that all hope of 2C is gone - and for many researchers, that's a very uncomfortable conclusion even to dally with, let alone endorse.

As the Cancun summit opens, the UK's Royal Society publishes that is given over to analysis of "a 4C world" - stemming, in large part, from .

As Oxford academic Mark New writes in the preface:

"Many emissions policy scenarios had (i) underestimated the rate of increase of emissions in the last decade and (ii) been unrealistically optimistic about when global emissions might peak, given the time it takes to transition out of carbon-based energy systems.

"A pessimistic, or some might say realistic, appraisal of the slow progress of the United Nations Framework Convention on Climate Change (UNFCCC) process, also suggested that avoiding two degrees would be highly unlikely, and that the chances of warming by four degrees in this century much less unlikely than previously thought."

Kevin Anderson and Alice Bows, presenting their analysis of pledges and pathways, write in stronger terms:

"Despite high-level statements to the contrary, there is now little to no chance of maintaining the global mean surface temperature [rise] at or below 2C.

"Only if Annex 1 nations reduce emissions immediately at rates far beyond those typically countenanced and only then if non-Annex 1 emissions peak between 2020 and 2025 before reducing at unprecedented rates, do global emissions peak by 2020."

No countries, whichever part of the world they're in, have pledged anything of the sort; which adds to the thesis that 2C is now a mushroom-seated, hookah-fuelled dream.

So what would a 4C world look like - or a 4C+ world, if you take 4C as a minimum - according to the projections contained here?

In some respects - rather blurred, you would have to conclude.

Robert Nicholls and others calculate that by 2100, it's plausible to think of a sea-level rise anywhere between half a metre and two metres - which in terms of the practicalities of protection, is a huge uncertainty.

But other specialists come to starker conclusions.

Philip Thornton and colleagues have this to say about food:

"The prognosis for agriculture and food security in Sub-Saharan Africa in a 4C+ world is bleak.

"Already today, the number of people at risk from hunger has never been higher... and it is estimated that it may exceed 1 billion in 2010.

"Croppers and livestock keepers in Sub-Saharan Africa have in the past shown themselves to be highly adaptable to short- and long-term variations in climate, but the kind of changes that would occur in a 4C+ world would be way beyond anything experienced in recent times."

The financial consequences of trying to adapt to all these changes are potentially huge. While is supposed to usher in a deal that will provide poorer countries with $100bn per year from 2020 for mitigation and adaptation, this report says:

"...the severity of impacts at 4C will require much greater investment"

... with the cost of sea defences alone being put at anything up to $270bn per year.

All in all, these papers conclude, it's over-simplistic to think in terms of 4C being twice as bad as 2C:

"A 4C+ world may require a complete transformation in many aspects of society, rather than adaptation of existing activities; for example, high crop failure frequency in southern Africa may require shifts to entirely new crops and farming methods, or sea-level rise may require the relocation of cities."

In so far as the scientists assembled here come up with a prescription, it is to increase research effort on the big unknowns (such as answering the outstanding questions on sea-level rise), take a new approach to adaptation so plans are implemented that can cope with a 4C+ world as well as a 2C world, and research geo-engineering technologies in case they need to be deployed at any stage.

Oh - and one more:

"The papers in this issue add urgency to the need to swiftly curb emissions..."

The fact that the 4C question is being seriously asked shows that for some, urgency is proving as elusive as a white rabbit in Wonderland.

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