Will paying countries not to cut down forests work?
The UN climate talks in Poland are at risk of faltering, with accusations from Green groups about Europe's failure to show the leadership it promised. BBC environment analyst Roger Harrabin has been following climate politics for more than 20 years. Here is his postcard from Poznan, addressed to his 10-year-old son.
My Dear Son,
It's cold and sunny in Poznan - a handsome old place fortified by towering buildings with tiny slits for archers to rain arrows on the invaders. You'd like it.
I am sorry our parting was a bit of a scramble, with the computer refusing to print your evaporation homework. I think we should do that experiment again because we can't be sure no-one slopped the salt solution.
On Monday a bunch of young people shut Stansted Airport complaining that my generation had failed them.
I am writing this postcard for you to read when you are 50, in case things go badly and you are wondering why we let it happen
I am writing this postcard for you to read when you're 50 in case things go badly and you are wondering why we let it happen.
There was a lot of uncertainty in the early days. We're still not exactly sure in 2008 how the clouds or oceans or forests or soils will react to us doubling CO2 in the atmosphere.
Young activists at Stansted airport asked world leaders not to fail them
Nor are we sure whether or when we'll hit tipping points which throw the planet into runaway warming, like the melting of the Arctic permafrost.
And there are still some economists who think we shouldn't be spending money on this climate stuff when there are still millions without toilets and drinking water.
But a lot of the arguments are mainly resolved and they are getting boring.
I tried to persuade one of my editors to run a climate change piece in a top slot on the radio. His eyes rolled back in his head, he slumped on to the desk and he almost drowned in the froth of his cappuccino.
This year, people are getting annoyed with the Italian and Polish governments, as well as others from Eastern European states, who are making the EU wobble over its policies to cut emissions by at least 20% by 2020 from 1990 levels.
You may remember that the same governments have acknowledged that, in order to be confident of a stable climate, rich nations do need to go much further - they need to cut between 25% and 40%.
The Arctic permafrost's vast reservoir of methane could become unlocked
You'd probably ask me why I didn't keep reminding everyone that it's the wrong target we're aiming at.
That's fair point, but I would say in my defence that the public is confused enough anyway with all the numbers.
I realise that by the time you are 50, the planet might be showing you that this argument was a bit pathetic.
I'm putting this card in an envelope to be read on your 50th birthday. I think it's a bit grim for a 10-year-old to cope with
But one thing you really cannot underestimate is the difficulty of an effective global deal. The world has never had to deal with a problem like this - trying to sever the link between our wealth and the fossil fuels that have brought us that wealth.
Hard to swallow
The financial crisis has made it worse. Some of the delegates here are furious at seeing trillions being stuffed into the accounts of firms who borrowed too much, when these sums are out of the question for stabilising the climate.
Environmentalists are also upset to see US politicians supporting their big car firms who lobbied successfully against laws to make their engines more efficient. Polluter paid, not polluter pays.
The younger generation will not be silenced
But if America plunges into lasting recession, there will be no cash to invest in the sorts of clean technologies we need to bring us energy without the greenhouse gases. So these decisions really aren't easy.
Now I've just had a Polish ham breakfast with three experts on carbon trading. They are fretting about certified emissions reductions verified additional under the Marrakech Accords.
They are right to fret - the system is not working. But I can't make carbon trading sound interesting and important… and their discussions are bogged down in detail too.
Young climate activists travelled to Poznan to make themselves heard
Some people here are optimistic about two things.
One is President-elect Obama who is set to throw cash at clean technologies and energy efficiency - but this will produce results much too late to meet the demands of the official scientists.
And there is a desperate and so far unfounded hope - that the Chinese might break the diplomatic superpower carbon stand-off, by making a unilateral offer on emissions that shames America into deep and sudden cuts.
I'm putting this card in an envelope to be read on your 50th birthday. I think it is a bit grim for a 10-year-old to cope with.
By the time you read this, I suspect you'll be taking the environment really seriously. Maybe.
Lots of love,
Will our children still be smiling in 50 years?