If you are worried by the threat of global warming the fear is that democratic societies simply won't be able to take the radical action necessary to tackle the problem.

If you believe the threat has been exaggerated you should be worried about whether democracy itself will be sacrificed in the name of action on climate change.

Indeed, democratic principles may already be being overridden here in Britain in the effort to reduce carbon emissions, as I discover in this week's Analysis programme on BBC Radio 4.

My last Analysis programme proved very controversial. We explored the provocative idea that the green movement might have hidden political agendas that could prove damaging to the environment. It even got the Analysis editor a grilling on Feedback - listen here:

The challenge climate change presents for and to democracy has been an issue I've been preoccupied with since the very early days of the so-called Ethical Man project.

The idea of Ethical Man was to see how much a well-meaning family could cut its greenhouse gas emissions without giving up all the trapping of modern life and moving to an isolated croft.

The project started out as an optimistic adventure into a low carbon world but ended up with a profoundly pessimistic conclusion - it is impossible for individuals to respond adequately; only a wholesale transformation of the entire world economy can achieve the carbon cuts the scientists say are necessary.

How did we reach this conclusion?

Our family did everything we could think of to reduce our greenhouse gas emissions - got rid of the car, stopped flying, turned down the thermostat, changed what we eat. Yet we only managed to cut our total emissions by just 20%.

Which is where the question about democracy comes in. Will people ever vote for politicians who will force us to make the sacrifices necessary to bring this transformation about?

The debate was thrown open a few weeks back when the visionary scientist James Lovelock dared suggest in an interview in the Guardian that maybe democracy might need to be suspended while societies grapple with the issue.

"I have a feeling", Mr Lovelock told journalist Leo Hickman, "that climate change may be an issue as severe as a war. It may be necessary to put democracy on hold for a while."

That was the jumping off point for our programme. Tell me what you think.

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Another described them as an "excoriating rabble of pestiferous vermin".

You don't express yourselves quite as colourfully, but your sentiments about the current expenses scandal are much the same.

A couple of weeks ago we asked you to tell us how this scandal - and all those others (non dom billionaire donors, cash for honours, Chilcot etc...) are affecting how you feel about politics and politicians.

It's part of a project Newsnight is calling Pop-Up Politics.

It's an all expense-spared, austerity approach to reporting the coming election.

The idea is that, just like the temporary shops that pop-up in the vacant lots on our recession blasted high streets, Newsnight will pop-up in your community to discuss the issues that matter to you.

We received hundreds of replies but one e-mail in particular caught our eye (and not just because it contained no profanity).

It was one of a number from Livingston, in West Lothian and was from Maureen Kerr who says she's lost faith in most of our politicians.

Maureen used to be a Labour supporter but is now backing the SNP and in recent weeks has been out knocking doors and handing out leaflets on their behalf.

"It is astonishing how big a percentage didn't want to vote at all because they think everyone is the same," she told me as I wheeled her golf bag around the local golf course.

She says eight out of 10 people she spoke to on the stump said they don't plan to vote.

"They are angry," says Maureen. "They feel they are being taken for granted," she says and worries at the damage this haemorrhaging of trust is doing to the political system.

So how can trust be rebuilt?

To try and get some answers we set up our own pop-up shop right in the heart of The Centre - Livingston's vast new shopping mall.

We rounded up 20 or 30 shoppers to take part in an impromptu debate. No fancy props for us, just a maker pen and pile of cardboard boxes.

There was a lot of talk about how the public has become disillusioned with our leaders. Then one woman said she thought that the problem was more complicated that that:

"We're not stupid," she said. "We know what is coming. We've seen what has happened to finances worldwide. So they don't trust the electorate.

"If they told us what's going to happen I think we could accept it because we understand there isn't the money around that there used to be."

It's an interesting perspective - the problem is as much about politicians not trusting us as us not trusting them.

Do you agree?

And, while we're at it, tell us where the pop-up politics team should go next.

We'll be covering the budget on Wednesday.

So, have you been affected by the recession? Do you believe that the politicians aren't being straight about how to get the country back on track? Or do you think people just don't understand the challenges they face?

Whatever you believe, tell us where we should pop up and why and who knows, we might come and watch the Budget with you.

Yet that's exactly what Transport Secretary Lord Adonis has done.

Lord Adonis wants to build high speed railway lines right up the spine of Britain, linking the country's major cities and punching through some of the most beautiful areas in Britain.

The White Paper detailing the route will be published next month and to symbolise the political consensus he hopes to secure for the project he invited Newsnight on an exclusive tour of Britian's only existing high speed line with two very unlikely fellow travellers - battle-scarred political opponents Lord Heseltine and John Prescott.

We joined Hezza and Prezza on a day trip along what the government now calls High Speed 1 - that's the channel tunnel rail link to you and me.

The 68 miles (109km) of high speed railway between London and Dover seem very modest when compared to the 3,600 miles of high-speed line in operation in Europe, but they would never have been built without the interventions of both veteran politicians.

Despite their ideological divisions (and the fact that Mr Prescott opposed the building of the channel tunnel) both men were instrumental in the construction of the channel tunnel rail link.

As Environment Secretary Michael Heseltine championed the route out through east London, while Mr Prescott was instrumental in saving the route from bankruptcy in the late 90s.

Now together they are supporting Lord Adonis' plan to bring Britain into the high speed railway age with a network the government is calling High Speed 2.

The high speed network he plans would slash journey times to Britain's major cities. Once complete you would be able to zip from London to Birmingham in just 45 minutes, to Manchester in one hour and 20 minutes and up to Scotland in less than three hours. Leeds would take an one hour and 25 minutes and you would be in Newcastle in two hours flat.

The big challenge will be maintaining a political consensus on the issue. Just look at how attempts to get cross party agreement on long-term care for the elderly degenerated into a political bun-fight last week.

Indeed momentum on High Speed 2 might be maintained by Lord Adonis himself.

There is a rumour in Westminster that the Tories are considering offering Labour's transport secretary the same portfolio if they win the election.

Lord Adonis told me he would not do that, but as our train sped back towards Stratford, Lord Heseltine suggested to Mr Prescott with a laugh and nudge that they might take the brief on together and see the project through.

That is unlikely ever to happen, but it will need a similarly visionary cross party initiative if Lord Adonis' grand vision for Britain's railways is to be rolled out across the country.

Watch the full report on Newsnight, Wednesday 17 February 2010.

It asks an admittedly deliberately provocative question - whether the green movement is bad for the environment.

But the actual programme is, I thought, more balanced and nuanced. It discusses whether some of the ideological baggage of the green movement can be a problem when campaigning on the climate issue.

Yet it led one contributor to the programme to describe me as dangerous. I've been called all sorts of things in my life, but that's a new one on me.

I've also had a clutch of critical e-mails. One described the programme as "an attempt to catch a currently fashionable vogue for smearing environmentalists".

Then there is the usual slew of angry posts on my blog.

This time even the producer has come in for flack. There have been pointed attacks on her article on the use of religious imagery by environmentalists. (But it has been posted up by Al Gore.)

So why is the programme causing such controversy?

A number of people thought it was plain biased.

"It's good old fashioned journo trick", reads a comment on one blog.

"Set up the straw man, conflate lots of ideas and different people's work behind it and deliver your own value laden conclusions as if you were taking the only rational position possible."

Is that fair? Judge for yourself, listen to it now.

Alternatively, you can read a full transcript here.

The more patient among you can wait until Sunday 31st, then you will be able to do it the old fashioned way and listen to the programme on the wireless. Radio 4 at 9.30pm. (You may it find a useful sleep aid).

But I will cut to the chase. I argue in the programme that green campaigners should be very wary of using the urgency of the climate issue as cover to push forward other, agendas - poverty or equality, for example.

Here's the conclusion: "I don't have a problem with people campaigning for those other agendas for their vision of a better society. For me the problem comes if the
fear of the consequences of climate change is used as cover to smuggle in other objectives for social and political change. That's because many people already
have a sense that there's something suspicious about the campaign to tackle global warming; they instinctively distrust the science and if they feel that the solutions people are proposing are less to do with carbon than pushing through a hidden agenda that will only serve to confirm their scepticism."

Now that's not that controversial is it?

It is a bombastic question - deliberately so. I set out to answer it for Radio 4's Analysis programme.

We explore how climate change challenges some of the the attidudes and ideology of the green movement and whether some green campaigning actually undermines the attempt to tackle the problem.

Tune into Radio 4 tonight at 8.30pm or on Sunday night at 9.30pm or just click here and listen to the programme right now .

The producer Helen Grady has written a fascinating article about it here here.

Do please tell me what you think and, as always, feel free to be absolutely frank!

It is an important issue - almost a quarter of world greenhouse gas emissions are from transport.

I have explored the relative carbon cost of almost every type of transport you can imagine.

I have even analysed the environmental impact of walking - and found that on one reckoning walking is actually more polluting than driving!

The fact is there are no straightforward answers.

Flying isn't as bad as you might think - pretty much the same carbon footprint as driving (except of course you are likely to go a lot further on a plane) - meanwhile public transport might actually be less carbon efficient than just hopping in your car .

But now I reckon I've got the definitive answer. I have found the world's most ethical form of transport.

Here's how it happened:

My blog on why cars might be greener than public transport caught the eye of the FT's devilishly clever "undercover economist" Tim Harford, who moonlights here at the BBC as the presenter of the Radio 4 programme More or Less .

Average occupancy

The programme had snuffled out some statistics from the Department of Environment, Food and Rural Affairs which confirmed my claim.

The figures show that the average occupancy of a British bus is just nine people. Even in London a typical bus has just 13 passengers.

Two people in a car produce lower emissions per person than nine people in a bus.

Indeed, the figures show that buses are only 20% more efficient than taking the car based on average vehicle type and occupancy.

But that's not what had snagged Tim's interest. He was intrigued by a claim I made at the end of the blog.

I argued that it is always more carbon efficient to take the public transport option because "it will be going anyway".

'Perfect excuse'

He wanted to know whether the same argument applies to flying. If the reason you catch the bus is that it will be going anyway then surely that's also true of your holiday flight to Malaga - it will fly with or without you.

In short, it is the perfect excuse for us all to continue flying around the world.

But will the buses and planes be going anyway? That's what Tim wanted to know and he invited me and the Independent newspaper's travel correspondent, Simon Calder to discuss the question with him.

Simon Calder is known as "the man who pays his own way" and is quite possibly the most travelled man in Britain.

He is also, it transpires, a mathematician. In short the ideal person to discuss this tricky issue.

You can listen to the programme here:

As our discussion demonstrates, the question is not as straightforward as it might first appear.

Are you actually responsible (at least in part) for persuading the bus, train or airline company to put on additional services?

Do you agree with Tim's argument that average marginal cost applies to buses and planes equally - or are you on my side?

(I should probably come clean here. I was very briefly an extremely junior economist at the Department of Transport. But don't let that affect your judgement.)

Impact of walking

You'll have heard from the programme that I suggest that for short journeys walking or cycling is preferable to even public transport, but my analysis of walking shows that it is actually pretty energy intensive - and the energy in our food tends to be pretty carbon intensive .

So what is the truly low carbon travel alternative? It was Simon Calder who suggested hitchhiking.

He says that his own personal offsetting scheme is to hitchhike wherever possible, arguing that hitchhikers do not generate additional traffic.

I think there a strong case for that. After all, the driver who picks you up at a service station on the M62 or on the verge of the A43 is extremely unlikely to have decided to hop in his car with the intention of picking up a hitchhiker (if he has I venture to suggest you are in real trouble).

What's more the additional carbon cost of you travelling with him will be very low.

I asked Simon why I hadn't seen him standing sodden in the rain at the end of the M1 and he said that's because now he's finally got rid of the German army greatcoat he wore as a teenager drivers readily pick him up.

But does anyone else hitchhike these days? You certainly see very few hitchhikers on the roads.

Festival flashback

I haven't hitchhiked for years but I can certainly remember my hitching days, and my best journey. That was heading to the Glastonbury festival back in the summer of 1986.

My friend Tim and I turned up at the end of the M4 and there were already 20 to 30 shaggy festival goers there already. Hitchhiking etiquette required that we join the end of the queue.

At this rate we wouldn't be at the festival until after Level 42 had played their set on the famous pyramid stage on the Sunday. (That's right, Level 42 were a headline band at Glastonbury - and people made a fuss about Jay-Z!).

But minutes later a lorry pulled up and said he'd take us all. We bundled into the back and sat on our sleeping bag rolls and rucksacks passing round the cider all the way to Somerset and were there in time to see The Cure (not to mention Lloyd Cole and The Pogues).

Not bad eh?

Do you have a better hitching story?

So the question for the New Year is how to ensure that the deal is improved on in Mexico - or wherever the next conference will be. Nothing ambitious, then.

First, though, we need to understand why Copenhagen led to such a disappointing agreement.

The answer is perhaps pretty simple. Indeed, the root problem seemed clear when the Ethical Man team went to India two and a half years ago.

I gave our report the rather provocative title Should Indians drive cars?. Our objective was to create an Indian Ethical Man. You can see below whether we succeeded.

The reason Copenhagen foundered was because most countries refused to set aside their narrow national interests for the long-term future well-being of the entire planet.

Ever since the dawn of the industrial revolution, economic development and hence national wealth has been based on the use of fossil fuels. And fossil fuels are still by far the cheapest and easiest form of energy.

What happened at Copenhagen was that most countries chose to try and protect their rights to go on using them.

The conference degenerated into the equivalent of a land-grab - not for territory on Earth, but for atmospheric space and the right to pollute it.

The environmentalist George Monbiot described it as "a scramble for the atmosphere comparable in style and intent to the scramble for Africa". He wrote from Copenhagen:

"Most rich and rapidly developing states have sought through these talks to seize as great a chunk of the atmosphere for themselves as they can - to grab bigger rights to pollute than their competitors. The process couldn't have been better designed to produce the wrong results."

But actually this was always the most likely outcome. This was, after all, a conference of nation states, and nation states exist to promote national interests.

Indeed, the conference was a graphic demonstration of the fact that what is in the best interests of a country is not necessarily in the best interests of the people who live in it.

So how can countries be persuaded to put the world first?

Gordon Brown says the process of negotiation needs to be reformed: "Never again should we face the deadlock that threatened to pull down these talks," he said in the wake of the conference. "Never again should we let a global deal to move towards a greener future be held to ransom by only a handful of countries."

It's a theme that has been taken up by the UN itself. Just before Christmas, Ban Ki-moon acknowledged that there were problems with the process and said he would consider how it could be streamlined.

The danger is that reforming the negotiating process is likely to lead to criticisms that powerful nations are trying use their influence to determine the outcome of the deal.

In the meantime, though, the diplomatic focus is on trying to persuade countries to increase the emissions cuts they have signed up to. Targets on cuts were not included in the Copenhagen accord and must by submitted by the end of this month.

That's when the real scope of the deal in Copenhagen will become clear.

But it is hard to be optimistic. It is rare that nation states put aside national interests for the greater good of the world. Can you think of any examples of when they have? Let's see how long (or short) a list we can come up with in the comments.

I'll chuck in the 1987 Montreal Protocol on ozone to get things started - undoubtedly a success, but nothing like the scale of what was being attempted at Copenhagen. A prize to anyone who can come up with an international agreement that involved anything like the sacrifice represented by cutting fossil fuel use. BBC guidelines may preclude that prize being a bottle of champagne - if so, I'll award an Ethical Man Award.

When my lovely daughter Elsa was born (our third child) I had to justify her very existence.

Her birth came half-way through my year of carbon cutting as the BBC's Ethical Man so my family life was under intense scrutiny.

I discovered that lots of people (who I am sure are very pleasant in their everyday lives) believe very strongly that the world is already full, and new Elsas are simply not welcome.

So is the burgeoning human population really the cause of our climate crisis?

It is easy to see why so many people believe that it is. People are responsible for greenhouse gas pollution, so - the argument runs - the more of them there are, the more damage they will do.

One reader of my blog last week asserted that "the human population could do with a good 25% knocked out."

He goes on to suggest that we should: "restrict every woman to a single pregnancy, once she has had that then sterilize her, restrict every man to causing a single pregnancy, after that castrate him, stop ALL forms of artificial preganancy (test tube etc.) This way we will reduce the population - and quite quickly."

Strong stuff! But it is certainly true that for the last couple of centuries population growth has been inextricably linked with the use of fossil fuels.

Indeed, the big mistake made by the original prophet of population doom, Thomas Malthus, was his failure to appreciate how fossil fuels would transform the world economy.

To be fair, it would have been hard to foresee, back in 1798, how industrialisation - powered by fossil fuels - would create the vast agricultural surpluses that would sustain a huge increase in population.

But his mistake points to the real culprit here: the problem is pollution not people.

Why? If we were to successfully "decarbonise" our economies then - in terms of the climate at least - the vast human population would not be a problem.

But that is a big "if". The distinctly lacklustre deal at Copenhagen suggests that the world isn't going to reduce greenhouse gas emissions anywhere near as quickly as the science says is necessary.

And the population is rising. You'll find no shortage of frightening statistics at the website of the new Malthusians at the Optimum Population Trust, which campaigns to reduce population. It details how world population is expected to swell from 6.8 billion this year to 9.1 billion in 2050.

But with the New Year looming let's not dwell just on the negatives.

The OPT's forecasts stop in 2050 and there may be a good reason for that. After 2050 it is expected is that world population will stabilise and then, very gradually, begin to reduce.

That's because there has been a dramatic fall in fertility worldwide.

The key figure in population statistics is 2.1. That's what is called the "replacement rate", the number of children per couple that would keep the population stable. Any higher than 2.1 and the population will rise, any lower and it will fall.

As recently as the 1970s only 24 countries - all of them rich - had fertility rates of 2.1 or below. Within the next few years the fertility rate of half the world will be 2.1 or less and will include countries like Brazil, Indonesia, China and even South India.

Sometime between 2020 and 2050 the world's fertility rate will fall below 2.1, at which point the long term trend will be downwards.

So while we undoubtedly face a population explosion now, pressure will ease over time.

And away from the queues and chaos of Copenhagen there is cause for optimism about the world's move towards a low-carbon economy.

On my travels around America earlier this year, I saw all sorts of exciting developments - technological breakthroughs, vast investment in renewable technologies, and a growing army of climate activists with friends in the highest places.

But the most inspiring thing of all was the sense that many Americans realise that a low-carbon energy revolution could be the key to America's future prosperity, kick-starting the American economy.

And, despite its obstructive position in Denmark, China also recognises the huge potential market of sustainable technologies too - make no mistake about that. The country is also investing billions trying to steal a march on the rest of the world.

Indeed, the coming decade should see an international race to develop the world-beating sustainable technologies.

The question now is whether these two trends - the move to a low-carbon economy and falling fertility - will happen fast enough.

But there is a further factor to consider when assessing how ethical it was to have Elsa.

Another commenter on my blog last week, Krupt, hits the nail on the head when he writes "20% of the worlds population consumes 86% of the world products and food. Bon appetite."

It's a theme George Monbiot explores here.

"To suggest", he concludes, "as many of my correspondents do, that population growth is largely responsible for the ecological crisis is to blame the poor for the excesses of the rich."

Which, unfortunately, still doesn't get me off the hook.

I know I'll be called a mean old Scrooge but here's the Christmas manifesto of this (former) Ethical Man: if you must give, give money.

I wrote these words two years ago but I'm pleased to see that more people seem to be coming round to this way of seeing things.

Professor Joel Waldfogel, who's been writing on the subject for far longer than me has been getting exposure in British newspapers and he gave a great interview to BBC Radio 4's More or Less programme.

The professor, author of Scroogenomics, is an economist. He's concerned about the $25bn of "missing satisfaction" incurred every Christmas, because gifts are under-appreciated. I'm more concerned about the carbon - but we reach the same conclusions.

You don't have to want Tiny Tim to starve in the workhouse to recognise what a bloated consumer nightmare the festive season has become.

Take my family, for example. We try to meet up over the Christmas period but I have mixed feelings about it.

Not because I don't enjoy seeing everyone and eating and drinking far too much before falling asleep in front of the telly. No, the reason is that I hate giving presents.

There you go you see - you are thinking I'm an old Scrooge aren't you?

Well I say bah humbug to that. I hate receiving presents too and here's why.

I've got three children and they have 10 cousins. If each of my children buys everyone a present that's thirty-six presents. If all the cousins do the same we're talking 13x12 presents - a staggering 156 in all.

And that is just the start. We've got to get presents for my folks, my three sisters and their husbands, my mother-in-law and her partner as well as my father-in-law, my wife's grandmother and her brother. Then, of course, they've all got to do the same for us. So that's another 9x8 presents - 72 more gifts - even if we assume that couples get just one present.

So my direct family alone could buy each other as many as 228 presents every single year and that's before I've popped over to my cousin Xand's for a mulled wine or two (another present plus one for my Aunt Anthea) or even begun to think about presents for friends (not that I do, you understand).

So why are these 228 presents a carbon catastrophe? That's simple: because every single one has a carbon cost. It wouldn't be a problem if this glut of gifts were actually useful. But be honest, when was the last time you actually got something you wanted or more importantly, needed?

My children now get so many presents that we collect up the ones we don't like and give them to the local charity shop. I know it sounds cruel, but we live in a small house and we would be engulfed in a veritable tsunami of tat if we didn't.

The real problem is that giving presents is an inherently inefficient activity. It means guessing what someone else may want or need. Every now and then you'll buy the perfect shirt but more often than not the ornament or tie or garden thermometer will end up in the attic or more likely in a landfill site and all the carbon that went into making it is completely wasted.

A few decades ago you probably needed the socks that your mum gave you or the saucepan she was given by her Aunt. These days it is different. Consumer goods are so cheap and plentiful that even people on very low incomes have no shortage of stuff.

Indeed, if you need proof of how corrupt our present giving culture has become look no further than the "gift" shops that have colonised every high street. You know the ones; they sell things no-one wants like scented candles, little vases and foot massage kits. Nevertheless they seem to do reasonable business.

Some of you may be thinking that I'm missing the point. You're thinking that present-giving isn't about the inherent value or utility of the gift but is about the act of giving itself.

I'll concede there's something in that, but gifts don't have to be useless. I've got a rule of only buying consumables as presents: food and drink (and sometimes fireworks). At least you know someone is going to enjoy them.

But surely it would be more ethical if we all bought each other stuff that you knew we really needed. Stuff like washing up liquid, toilet paper and breakfast cereal. Or better still, cash.

I've never understood why giving money is considered bad form. Wasn't that £5 note folded into Granny's card the very best present of all? You could use it to buy something you actually wanted. Not only that, until you buy something, cash is completely carbon free.

Hence my Christmas manifesto.

It was certainly the hardest thing I did during my "year of living ethically" for the BBC.

But Adolf Hitler managed it and so did Linda McCartney. Indeed, the government's former chief economist says we should all do it.

Are you there yet?

Yes, I am talking about giving up meat. Or, in my case, giving up all animal products.

But I should warn you we started our exploration of the ethics of what we eat with a lustrous Norfolk Black turkey chick we named Ned.

We watched him grow into a magnificent one-and-a-half stone stag... and then came Christmas.

Viewers with a sentimental nature should NOT watch this film.

I said at the time that I regretted not killing Ned.

"An ethical man should be able to stomach dispatching his own supper or should decline to dine upon it, shouldn't he?" I wrote.

And I am sure lots of us carnivores would be a lot less keen on our mixed grills if we had to look all the animals that go into them in the eye before they were served up on our plates.

But this blog isn't about sending you on a vegan guilt-trip - though if that's what you want, you can learn more about the mechanics of turkey slaughter here.

Neither is this blog about the bizarre animal ingredients I discovered might be lurking in even the most innocent-seeming foods - bread anyone?

It is also not about the incredible health benefits I experienced from my brief flirtation with ethical eating - I shed 2kg in 31 days and saw my cholesterol level plummet from 5.6 mmol/L (rather high) to just 3.4 mmol/L (very low for a man of my age).

Nor is it about how the food we eat is destroying the planet. Everyone knows that now - though, if you will allow me a little boast - we in the Ethical Man team pretty much got their first.

So what is this blog about?

It is about another aspect of the food we eat - the threat of an impending food crisis.

There was a hint of what could be to come back in 2007-8 when world food prices soared leading to food riots around the world.

Well, don't imagine that the worldwide depression has got us off the hook. Food prices have risen dramatically this year even as economic activity has fallen.

According to the UN Food and Agriculture Organisation (FAO) a billion people on earth will go hungry this year - one in six of the world's population. That's a thought that will haunt you as you sit down to enjoy your Christmas dinner isn't it?

But, lets be clear about this, there is no shortage of food in the world. Agricultural output is pretty near its historic high. So why are so many people going hungry?

The problem is that, increasingly, we don't actually eat the food we grow. Some is converted into bio-fuels - and rising oil prices makes that more profitable - but even more is used to fatten up the animals so many of us eat.

There has been a huge increase in meat consumption around the world in recent years. That trend should be a cause for celebration because it reflects that fact that people in developing countries are getting significantly richer. One of the first things people do when their income rises is to buy themselves some meat.

The problem is, these trends - coupled with population growth (which I will be discussing next week) - mean there is unprecedented pressure on food supplies.

The FAO estimates that by 2050 the amount of food available in developing countries will need to double - which is the equivalent of a 70% increase in food production.

We would need a lot less if people stopped eating meat because it would require so much less land.

It is yet another powerful argument for changing our diet. So the question is: how can we get people to change what they eat?

We can try persuasion, working through some of the arguments, as I have here. But don't underestimate how difficult it is to change people's behaviour on this.

If you want a measure of just how tough a problem this is to crack, look no further than me.

I know the arguments pretty well (I hope you will agree) and I've experienced the health benefits first hand. But I will still be sitting down to a turkey dinner come Christmas.

So perhaps some gentle coercion might therefore be more effective. There is already a lobby for "fat taxes" - higher taxes on fattening foods. It is a short step from there to taxing foods that have an adverse impact on the environment.

But would any politicians have the courage to impose a tax on meat? They are reluctant enough to impose taxes on other, more directly polluting, behaviours.

There may be other ways - please use the comment box below to send in any ideas you have - but, in the meantime, I have two suggestions for determined meat eaters who want to reduce the environmental impact of their food.

First off, eat less meat - that's something my family is doing (though not this Friday).

The second is even more straightforward, actually eat the stuff you buy!

In developed countries a quarter of all the food that is produced goes uneaten, most of it no doubt growing mould at the bottom of all our fridges.

So here's a festive challenge: I want you to craft that limp carrot, half-eaten packet of cheese and the remains last night's pizza into a delicious Christmas spread. It has to be possible to rustle up something palatable... doesn't it?

It sounds unthinkable doesn't it? But when I became a temporarily became a vegan for Newsnight, I developed a keen interest in what goes into the food I eat and I discovered that a food additive which is sometimes produced from human hair can be used as an additive in some baked goods.

But first, the veganism. I did not do it out of high principle. The idea was to test the claim made by a number of people who e-mailed in to insist that becoming a vegan significantly reduces one's impact on the environment.

I was vegan for one month- January 2007. So this did not preclude me eating Ned the Newsnight turkey for Christmas 2006.

I am happy to report that Ned was as tasty as he was ethical. My family gnawed our way through his ample carcass over the course of a full week. We ate Ned roast on the big day, then sandwiched, curried, as a supreme and finally in a tasty soup. Then, as the last few slices of Ned grew an extravagant mould in the bottom of our fridge, the New Year turned and my diet became completely meat and dairy free.

It wasn't easy. I did not just cut meat and fish out of my diet. Vegans don't eat any animal products including milk, eggs and honey. So did cutting out all animal products reduce my carbon footprint?

I need a bit of persuading about the bees but cows certainly produce an impressive quantity of greenhouse gases - some 500 litres of methane a day per animal.

When my vegan experiment was just getting under way, the then environment minister David Miliband pointed out at a conference that "the livestock sector generates more greenhouse gas emissions than transport". Agriculture is reckoned to account for 7% of all greenhouse gas emissions, about the same as aviation.

And methane isn't the only issue. It is claimed that one acre of arable crops can produce enough food for up to 20 people. Turn that field over to beef production and it will feed just one person.

Not only that, raising animals is a lot more carbon intensive than growing vegetables. David Pimentel, an ecologist from Cornell University, has calculated that animal protein production requires more than eight times as much fossil-fuel energy than plant protein yet yields proteins only 1.4 times as nutritious for humans.

That's the average. When you look at individual sectors the figures are even more startling. Take beef, for example. Using US Department of Agriculture figures he found that beef production requires an energy input to protein output of 54:1 (as well as 100,000 litres of water per kilogram of meat).

Vegetarians shouldn't feel too smug, though. Milk protein has a ratio of 17:1. In fact, rather depressingly the most efficient form of animal production - perhaps not surprisingly - is battery chickens. Pimentel finds that broiler chickens have a ratio of energy input to protein output of just 4:1.
My problem has been eradicating all these inefficient animal proteins from my diet. Take my very first day of vegan living, New Year's Day.

I hadn't prepared very well and hadn't got any margarine in. The local corner shop, a Londis, was open and they stock a good range so I wasn't too worried. But as I worked my way through the eight or so different varieties of margarine I was amazed to find that every single one contained milk or dairy products in some form.

It makes you realise just how common the use of animal products in food is. Before I became a vegan I would eat animal products in every single meal. Indeed the Vegan Society points out that some vegans consider tap water unacceptable because it contains chemicals that have been tested on animals.

I am not going that far but I have certainly developed a mania for reading food labels and there are all sorts of unexpected animal additives.

Most people know that gelatine is produced from animal skin and bones and that the rennet used in some cheeses comes from calves' stomachs. But did you know that bone char (from cow bones) is still occasionally used to whiten some sugars or that some wines and many beers (particularly real ales) include isinglass - a substance obtained from the swim bladders of fish?

Which brings me back to the possibility that human hair may be used in bread. A vegetarian friend alerted me to the existence of an animal-based flour additive called L-Cysteine. It is an amino acid which is used as a flour improver. It is known as E920 and is permitted for use in all biscuits, breads and cakes except those that claim to be wholemeal.

The problem for a would-be vegan is that traditionally L-Cysteine is produced from feathers, pig bristles and sometimes even human hair. These days L-Cysteine can also be produced synthetically but apparently human hair remains one of the richest sources of this amino acid - it makes up about 14% of your hair - and there is a small industry in China making the additive from hair clippings.

There's even a paper on the web written by a Rabbi about whether L-Cysteine from human hair is kosher. Apparently it is - so long as the hair in question was not harvested from dead bodies.

So how commonly is L-Cysteine used? My vegetarian friend claims that the problem with E920 is that - even when it is used - it doesn't have to be listed in the ingredients. She says that's because it is broken down in the baking process so the manufacturers argue that doesn't constitute an ingredient.

That is something the Food Standards Agency flatly denies. It says that L-Cysteine must always be labelled. Indeed, the industry says the reason you so rarely see E920 on labels is that these days it is very rarely used (apparently it was much more common fifteen years ago). The industry also says that the only L-Cysteine their members would use is the synthetic variety.

That is a little odd because according to the Food Standards Agency the European regulation specifies that only L-Cysteine produced from duck and chicken feathers or from pig bristles can be used. That means that, so long as your daily bread was baked in Europe, it almost certainly does not include human hair.

But it's a little confusing. If British bakers are using synthetic L-Cysteine are they breaking EU guidelines? It is hard to get a straight answer. Biscuit makers told me it would be added when the flour is milled - and the millers say it's something the bakers would add.

So if anyone can put this hairy issue to bed once and for all I'd be very grateful. And while I am on the subject, if anyone knows of any other animal-based (or human-based) food ingredients a vegan needs to steer clear of, please do tell me.

NB - Look familiar? This blog is made from 100% recycled material from Justin's 2007 Ethical Man series - keeping it ethical.

We are lucky here in Britain to be home to the most august scientific institution in the world, the Royal Society. It celebrates its 350th anniversary next year. Its motto is "nullius in verba" which means "take nobody's word for it" - which is pretty much a charter for scepticism.

It is a fitting motto, because healthy scepticism is the foundation of good science.

The urge to question accepted truths, to doubt received wisdom, to investigate things for yourself, is the basis of scientific enquiry.

So let's not damn people for being sceptical of the climate science... unless, that is, they don't make the effort to make a reasonable examination of the evidence.

The opinion polls suggest that almost half the people in Britain are not persuaded that man is causing global warming.

So Newsnight decided to do a little (and very unscientific) experiment of our own.

We challenged two leading British scientists to try to prove the science of global warming to a group of people whose views very loosely reflect national opinions.

And, as if that wasn't tough enough we asked them to do it in my kitchen.

Can they do it? Well, you can see for yourself.

Obviously, we had to radically cut down the scientists' presentation to squeeze it into the tight TV time constraints but if you want to dig a bit deeper into the science of global warming the best place to go is the Intergovernmental Panel on Climate Change.

The Science Museum's site is more accessible to non-scientists, or you might try the Meteorological Office's site which has a section on climate change science. There's also loads of stuff here on the BBC site.

Get stuck in!

I'm happy to celebrate the instinct to question authority because scepticism is also the basis of journalistic enquiry.

Right from the get-go, the idea of the Ethical Man series was that it should be a sceptical inquiry into what ordinary people can do to reduce their impact on the environment.

That's why I have no problem reporting that micro wind turbines don't work or that cars can sometimes be more carbon efficient than public transport - if that is what the evidence suggests.

But not everyone is comfortable with scepticism.

A couple of days after my blog on cars was published, I was shocked to find an e-mail from an environmentalist who said it should never have been posted. He made no effort whatsoever to refute my claims, his argument was simply that it undermined the debate to publish such heresy.

That instinct to suppress evidence that challenges preconceptions is very dangerous. Any hint that the climate change science is anything other than transparent will - understandably - encourage people to be even more sceptical.

If it looks like that's what people are trying to do, the scientific community should be very clear in its condemnation - as Sir David King, a former chief scientific adviser to the government, was in my kitchen.

Because, if our "experiment" says anything it says that people are hungry to understand the science of global warming and that when the evidence is explained clearly, lots of people find it very persuasive.

So let's celebrate scepticism and follow the Royal Society's injunction to interrogate accepted wisdom. But let's do it with an open mind and on the basis of a reasoned examination of the evidence.

That's how scientific hypotheses get proved and - yes - disproved. And wouldn't it be great if someone proved the science of global warming was wrong?

We are told we have to stop flying, stop driving, stop eating meat, stop heating our houses... the list goes on and on.

So it is a nice change to be told that there is something you can do which will reduce your impact on the environment AND requires that you buy yourself a nice bit of kit to boot.

Bring on the domestic wind turbine!

What could be more environmentally friendly than harvesting electricity from the wind and what better ethical badge of honour than a turbine spinning on my roof?

That's certainly what I thought three years ago, when my family and I were challenged by the Newsnight editor to try to make our lifestyle greener.

Unfortunately, I wasn't the only wannabe ethical man to want to reap the wind. As I began exploring the possibility of erecting a turbine on my terraced London home the Tory leader David Cameron announced his ambition to do the same.

The question was, who would get theirs up first?

Three years on and neither I nor the Tory party leader have a turbine on our roof.
Why?

The answer is very simple. In most urban locations in Britain wind turbines simply do not work.

Yes, they spin, but they do not generate significant amounts of power. Why not?

Here's the science bit... (don't worry, you will be able to follow it).

A simple equation gives the power of the wind. Power = 0.5 x collection area x the wind speed cubed.

What it tells us is that the power of a turbine is related to two factors: the size of the turbine and the strength of the wind.

Let's look at size first.

Cast your mind back to your GCSE maths (I'm old enough to have done O-levels). No doubt you dimly remember that the area of the circle is equal to the constant pi (3.14) times the radius of the circle squared.

What that means is that as you increase the length of a turbine blade, the collection area increases disproportionately.

Take the micro turbine I was planning. Its blades were 1.75m long, giving a collection area of just under 10sq m. Tiny.

Compare that to the wind turbines I visited in Texas earlier this year. Some had turbine blades 45m long, giving a collection area of 6,358sq m. Huge.

The message is clear from the maths - small turbines have disproportionately smaller collection areas and therefore generate dramatically less power.

And what about wind speed?

The key here is that cube function on the wind speed. The power of the wind is related to the cube of the wind speed. So, at low wind speeds you get virtually nothing. When it really blows it you get a lot of power.

Here's why. Double the wind speed and you get eight times the power. Quadruple it and you get 64 times as much. Eight times the speed and we're talking more than 500 times the power.

The figures given by Windsave, the company that was going to install my wind turbine, confirmed that.

It boasted that its 1.75m turbine would generate 1kW of power at speeds of 12.5m per second.

Pretty good, but 12.5m per second is a force 6 wind, a decent breeze.

Halve the wind speed to six meters per second (a moderate breeze) and - thanks to that cube law - you now get just 120 Watts - that's two standard incandescent lightblubs (10 energy friendly compact fluorescents).

Hum, not bad.

My house is on the flanks of the highest hill in London and is relatively exposed but I'm told that average wind speeds are likely to be between 4m and 5m per second. (You can find out the wind speed in your area here.)

At those speeds I'd be lucky to get 25 Watts. That is barely enough for two energy saving light bulbs. Nowhere near enough to live up to the company's promise of reducing my electricity bills by "up to 30% a year".

The message is clear. In most UK locations micro wind turbines will never generate significant amounts of electricity.

It makes a nonsense of the claim made by the Energy Saving Trust, when I was planning my turbine, that domestic wind turbines could supply 4% of all the UK's electricity needs and cut carbon dioxide emissions by 6%.

It also suggests the government should think again about offering a generous feed-in tariff for power generated from micro wind turbines.

And, if any more proof of my point was needed, in September this year Windsave went bust.

Of course, not all wind energy is a dead end. What our calculations tell us is that power increases dramatically as you increase the size of the turbine and the wind speed. So, a 10m turbine in a 10 knot breeze generates 100,000 times the power of a 1m turbine in a 1 knot breeze.

Indeed, if Camden, my local council, gave me planning permission for one of those Texan whoppers it would generate significant power - something like 200kW - even at 4m per second.

But even these impressive figures can't disguise the inconvenient truth about wind power: except in storm conditions it is - compared to fossil fuels - a very dilute energy source.

Professor David MacKay, the new chief scientist at the Department for Energy and Climate Change, has done the maths on this. Instead of kW, he calculates power in kWh, and he estimates that if we put wind turbines across the windiest 10% of the country, we would generate only 20 kWh per day per person in Britain.

According to MacKay, it takes 40 kWh to drive the average car 50km.

Add in offshore turbines covering a third of the available shallow water locations (44,000 turbines) and installing deep water turbines in a 9km-wide strip all round the entire British coast and you get an additional 48kWh day per person.

That's a lot of power, but even on quite conservative estimates the average UK resident uses 125 kWh day.

It leads to a dispiriting conclusion. Wind is, at best, only a very partial solution to the problem of how to generate low-carbon energy.

It isn't as easy as you might think.

Three years ago, I pondered the problem with the Ethical Man producer, Sara, for a couple of days before we had a moment of genius.

Our solution infuriated my wife, enraged my colleagues and alienated a large section of our audience but I still stand by it.

So what was this brilliant idea?

We decided that I should illustrate the impact of flying by jetting off for a weekend in Jamaica.

I know. That's what my wife thought too.

And to make matters worse I filmed the moment I revealed our plans to her. You can watch my marriage disintegrate here.

Please tell me if you think our approach was misguided.

For the record, here's my defence. We reasoned that if you watched our film and thought the idea of a man calling himself "ethical" flying off to Jamaica for the weekend smacked of hypocrisy, it might make you reflect on your own behaviour and consider flying less.

And, because we were keeping a tally of my carbon footprint, we reckoned the record of my flight would serve as a reminder of just how carbon-intensive flying is.

I did say this at the time but, judging by the avalanche of outraged emails we received, it fell on deaf ears.

The truth is, flying is the single most intractable climate change issue.

There is a solution to most of the other stuff - we can cut our energy use, change how we generate power, drive electric cars, eat less meat etc... but there is no alternative to flying.

And how we love to fly. A least one foreign holiday a year now seems to be regarded as pretty much a right of citizenship. Which is why politicians are so worried about stopping us doing it.

Why is flying such a problem?

Let's start with the good news: a couple of years ago I looked into the numbers and found that modern jet aeroplanes are actually a very efficient form of transport .

The jet engine is actually one of the most effective ways to convert the energy from fuel into thrust. The best jets are 37% efficient. By contrast modern petrol engines are around 25% efficient while a finely tuned diesel will achieve, at best, 32% efficiency.

How does that translate into actual fuel consumption?

Take a look at some figures: my old car - a two litre petrol Saab 9-5 estate - uses 8.6 litres per 100km.The most efficient cars do better than that. The Toyota Prius, for example, is much more frugal. It uses 4.3l/100km.

So what about aircraft? The average jet plane now uses around 4.8l/100km per passenger - just a little worse than a Prius with no passengers. But the manufacturers say modern jets are much more efficient.

Airbus claims it makes the most efficient aeroplane currently flying, the A380. It says this behemoth uses just 2.9l/100km per passenger. (Here's the dull bit: that's the fuel consumption when you assume a three class configuration operating at capacity with 525 passengers.)

So far as I can tell, the latest jumbos are similarly efficient - it is hard to be certain because the manufacturers do not publish comparable figures - but Boeing's 747-8 uses 3.7l/100km per passenger when operating at 70% capacity. (Assuming it is configured to hold 470 passengers in three classes.)

So, if jet engines are more efficient than car engines why do they get such a bad rap?

The anwer is pretty obvious - we use planes to travel extremely long distances. That weekend in Jamaica racked up just over 15,000km. That's pretty much what the average British driver would do in an entire year.

The other problem is that planes release their pollutants high up in the atmosphere where they have an even stronger greenhouse effect. The process is known as radiative forcing and means aircraft emissions are reckoned to be almost twice as damaging as emissions at ground level.

So, combine the distance you fly with the effect of radiative forcing and you can see why our appetite for air travel is so worrying.

You can do as I did - get rid of your car , switch to energy efficient bulbs , eat locally grown food - but take one holiday flight and you will erase all your careful carbon cuts.

So what are the alternatives?

Here's the rub. As my figures show, even if you did take the car instead of the plane you would still emit huge amounts of carbon, because of the vast distances covered in most journeys by air.

I've already done the maths on trains and buses. If you pack them full of passengers they will offer some carbon savings but, like cars, they leave the tricky little challenge of crossing oceans. Boats will do that job but there's a hefty carbon price to pay there too.

And these alternatives ignoring perhaps the most important feature of flying: it is extremely fast.

Lots of environmentalists regard speed as some kind of crime but much (not all) time spent travelling is time not spent doing something else - often a productive activity. So there is an economic cost to slow travel.

So what's the answer?

It's a tough one isn't it? Do write in if you've got any good ideas.

In the meantime how about this: establish a price system that accurately reflects the impact that carbon emissions have on the environment? That way the price of a plane ticket would include all the costs of our holiday.

It would mean we would all fly less, of course. But, given the problems my weekend in Jamaica caused me, maybe that would not be such a bad thing.

Read on, because I will tell you how to just that. I will show you how to take a substance we all throw away and convert it into something useful.

The discovery came at a high price. It involved making one of the most humiliating television reports ever broadcast by the BBC.

BE WARNED: this report features nudity, public urination, a surprising swimming pool sequence, a discussion of one of our most taboo topics and a shocking shower cap.

It also features footage of a minor celebrity in his Speedos - can anyone spot him?

So what has saving water got to do with making a fortune?

The answer lies in that back garden in York, featured in the video. What I saw there led me in search of the man who inspired the system.

And - three years later - I managed to track him down in his cabin in the backwoods of Pennsylvania.

The man I met in his home in the woods earlier this year has developed a revolutionary new system for dealing with one of the most fundamental processes on earth. By doing so he has become an inspirational leader, not just for John in York, but for tens of thousands of people around the world.

He has - how shall I put this? - started his own movement.

He's called Joe Jenkins and is the author of The Humanure Handbook, the world's first guide to composting your own poo.

That's right, the book that Britain's "king of compost", John Cossham, says "changed his life".

Obviously, I am alive to the comic aspects of these two men's obsession but the problems caused by human sewage are no joke. Sewage pollutes water and spreads disease. Millions of people around the world die every year from illnesses spread by sewage.

It is expensive too. Joe claims that we each produce over a kilo of the stuff every day - a total of half a tonne a year. That's 30 million tonnes of human sewage every single year in Britain. Disposing of all that waste costs hundreds of millions of pounds a year.

Which is where Joe's system comes in. Instead of regarding human excrement as a waste product Joe sees it as something that can be useful.

Our sewage is full of nutrients: "faeces and urine," writes Joe in his book, "are examples of natural, beneficial, organic materials... they are only waste when we discard them."

What Joe's composting system does is capture those valuable nutrients and return them to the soil.

Joe collects his and his family's waste and converts it into a rich compost which he uses to fertilise his garden. Thereby, says Joe, "closing the human nutrient cycle".

I ate a venison chilli Joe prepared with "humanure" fertilised tomatoes from his garden. Delicious!

Of course the idea of composting human excrement is not new, people have been doing it for millennia. What Joe has done is brought a scientific approach to the process. He has shown that, when composted properly, all the pathogens in poo are destroyed.

He has also demonstrated that "humanure" composting can be done almost anywhere. There are composting toilets based on Joe's system everywhere from Manhattan apartments to yurts on the Mongolian steppes.

And Joe's experiments with "humanure" can cut carbon emissions. It takes huge amounts of energy to fix the nitrogen used in most commercial fertilisers and they cause the release of huge amounts of nitrous oxide from the soil. And nitrous oxide has 296 times the global warming power of carbon dioxide.

Greenpeace estimates the effects of nitrous oxide and the emissions from the energy required to make fertiliser together account for almost half of all the direct emission from agriculture - that works out at almost 5% of total world greenhouse gas emissions!

Joe is convinced that large-scale "humanure" production could become a source of low-carbon fertility for the soil.

It could also reduce the 3.4% of the world emissions generated by waste processing.

This year, Joe has been exploring how his composting processes can be scaled up. He's had an intern from a local university working full time on the project. The ultimate aim is to make composting human waste into an industrial process.

His book and sales of his toilet system have earned Joe a very comfortable income.

The fortune will come if he can achieve his dream - spreading "humanure" across the world.

So who wants to take this technology on? Are you ready to install a composting toilet in your house?

(You will be pleased to know that, in keeping with the ethos of the Ethical Man project, this article is recycled from a previous post. Also, Francis Maude is now Shadow Minister of the Cabinet Office rather than Chairman of the Conservative Party, as he was in 2006 when the first video was filmed - but there is no reason to suppose that this has changed his approach to composting.)

Update 1545 30/11/09: Some eagle-eyed readers spotted a mistake in my copy (see comments below). This has now been corrected.
Update 1600 30/11/09: In the interests of clarity, the change referred to above was made yesterday.