A flight that almost cost me my marriage
Here's the challenge: how do you illustrate, in a television report, the impact of flying on the environment?
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.
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.