Most of us are lucky enough to have four walls and a roof to call home. To make it feel like home too we have systems in place to light, heat, cool, supply water and power for all the mod-cons. Naturally these all use energy and the vast majority of energy used in this country comes from fossil fuels. Most of us use a mixture of  fossil fuels supplied directly  (Oil, Gas and Coal) and Electricity, which, unless you are already one step ahead of the game and use electricity from renewable sources, will be made by burning fossil fuels.

Fossil fuels are full of carbon and when we set fire to them to release the energy we need we unfortunately end up pumping all of this carbon into the atmosphere. So to calculate our Green Debt we need to know how much of these fossil fuels are burned for the benefit of our homes each year. Thankfully the energy companies that supply tend to tell us exactly how much we use either monthly, quarterly or annually. Once we know the amount of each fossil fuel we are each using we can work out how much carbon is released when these fossil fuels are burned. This information is supplied by the government:

National Energy Foundation (uses information from DEFRA)

For electricity, the Fuelmix website tells us exactly how much carbon each electricity producer produces when they're generating your electricity.

So all we need from you is the amount of each fuel you use each year. There are two ways to provide this information. The most accurate is to look at your bills and see how much of each fuel you are using. If you can't find your bills, or want a quicker fix, then you can estimate how much you are using by telling us what you spend on your bills for each fuel. We need to use this information along with information on the average price for that fuel to estimate how much you have used. You may be paying more, of if you're lucky, less than the average so this isn't as accurate but probably won't be far off.

The average price information we have used has come from the following sources and will be regularly updated:

Electricity and Gas
Oil
Coal - Standard
Coal - Smokeless

To give you an idea of how this works, you can use the table below to work out how much carbon your electricity usage produces.

Electricity
Period	KwH used	Cost in £	Annual Carbon
P:  Annual Quarterly Monthly	KwH	£ 10p/KwH

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For many of us our cars are an indispensable part of modern life. They allow us almost complete independence of travel - we can go where we want when we want whilst sitting in a comfortable chair with music, telephone access, air conditioning - all the modern comforts we could wish for. Put like this it sounds like an experience that should be pretty expensive but in reality it's dirt cheap. The energy needed to move not just us but a couple of tonnes of metal glass and plastic 40 or 50 miles can be purchased for a few pounds and most of that goes to the government - the true cost is less than one pound even with today's high oil prices. In this section of the Green Debt calculation you'll work out the hidden 'cost' of travelling in your car - the carbon dioxide produced when your car's engine burns petrol.

At the end of the 1990s the government decided to base the tax rate for company cars on their carbon dioxide emissions. Ever since 2000 car manufacturers have had to tell us the carbon dioxide produced per kilometre of travel for all their new models. All of this information is available at a government website:

VCA Car Fuel Data

You should note that there is some controversy over these figures. Some people believe that they underestimate true Co2 emissions because they are based on laboratory tests that do not replicate actual driving conditions. There's likely to be some truth in this but it's extremely difficult to establish just how much the figures are underestimated and therefore we've used the figures as they are to give a consistent result across all makes and models.

We've taken this information from the VCA website and built it into our own database to make it easy for you to work out the Co2 rating for your car. The data's not provided for pre 2000 vehicles - you'll need to find the closest match you can in the 2000 models list.

Once you have selected the Co2 rating for your car using the drop down lists you'll need to tell us:

1 How many miles that vehicle travels in one year.

2 The percentage of these journeys that 'you' (you here means you + others you are including in the calculation) are involved in. This can often be a difficult figure to estimate as not only do you need to take into account the percentage of journeys that you are in the car, you need to factor in the number of people that are with you when you travel. For example, if you travel every journey on your own your sharing percentage would be 100%, but if you share all of these journeys with another person your sharing percentage would be 50%. Perhaps the easiest approach is to say that the all of the journeys that the vehicles makes during the year needs to be split between everyone who uses the car and you have to estimate what's a fair percentage of that split to include in the calculation that you are doing.

This information is then used in the following formula:

Miles x 1.609 x (Co2 rating/1000) x  sharing percentage = Annual Debt from Driving

The 1.609 is to convert miles to kilometres (as the Co2 ratings are expressed per kilometre). We have to divide the Co2 ratings by 1000 as they are expressed in grams and we need a kilograms figure.

You can do this for as many vehicles as you like and you can do amend the mileage and sharing percentage figures for each vehicle without having to delete that vehicle and start again.

The instructions for this section tell you what to do to get a fair result if you own a motorbike or you have a car that has been converted to Liquid Petroleum Gas ("LPG").

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This is a highly controversial area. There's a large number of online calculators that have sprung up (often as a basis for offering offsets). Unfortunately there is no agreed standard calculation method and an identical flight typed into one calculator can produce wildly different results to another calculator.

The government is hoping to introduce a standard in this area soon, but until then we have started from basic principles and come up with what we believe is a fair calculation taking into account as many factors that is reasonably possible.

One of the key reasons for the wide variation in figures is the 'flight multiplier' used to represent the greater warming effect of releasing carbon dioxide high up in the atmosphere (and other warming exhaust products from flying). This is explained in greater detail in the 'wider impact' section below. This is a controversial area and as such we believe we are unique in offering users of My Green Debt a choice as to whether to include a multiplier or not. There are arguments for and against - we'll let you make the final decision.

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Working out how much Carbon Dioxide is produced by each flight

It's fairly easy for chemists to work out how much carbon dioxide is produced by burning kerosene (aviation fuel). If you are interested there's a very brief article here which neatly explains how. That's the easy bit, the difficulty comes to converting this figure into a Co2 per passenger mile of flying.

To do so you need to make assumptions about the size of the aircraft, the level of occupancy, the mix of business, first and economy seating... the list goes on. Inevitably with so many assumptions there's a range of different estimates out there.

If you carry on reading the article you'll see they get a 'Co2 per mile of flying' figure of 0.2721 kg. This is based on data from 2003.

British Airways claim a figure of 0.1609 kg as an average across all of their flights (2006) (from 'How To Live A Low Carbon Life' by Chris Goodall).

The UK Government (2007 - Act on Co2 calculator assumptions) use three averages. Domestic = 0.2771 kg, Short Haul International = 0.2280 kg, Long Haul International = 0.1842 kg. The logic behind the different figures is a large amount of fuel is used taking off and landing. For short haul flights there are less miles to spread this load so the kg per mile figure will be higher.

These differences in these figures can be explained. The first figure is a little old and since it was calculated in 2003 airline occupancy rates and fuel efficiency have improved so we'd expect the more recent figures to be a little lower. British Airways have a higher proportion of long haul flights and it's probably fair to say that faced with uncertainty in their calculation they would have selected favorable assumptions in order to keep the figure low.

We've decided to use a figure of 0.21 kg per mile for our calculations as a reasonable mid point of these figures. We'll keep this under review and make changes in line with information that becomes available.

We do make an adjustment to this figure to take into account the flight length. We've used the UK Government data to come up with the following formula which can be applied to the flying miles to replicate their results for longer and shorter flights:

Green Debt from Flying = 0.21 x (Miles flown + 125 - (Miles flown x 0.15))

This means the longer your flight, the lower the kg per mile will be. An average flight of 833 miles (London to Rome) will be have the average figure of 0.21kg per mile.

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Economy, Business and First Class

This is an important factor in working out your Green Debt from flying. It's only fair to allocation a higher proportion of the carbon produced by each plane to the passengers in business and first class as they take up proportionately more room. It's not easy to work out exactly how to approach this allocation. Aircraft are different sizes with different size seats - it's difficult to be precise without taking into account all of these factors. Very few people know such precise details about their flights so we've come up with a calculation that approximates the effect of flying in different classes. It may not be precise but we think it's a reasonable estimate:

1 - We've got the average 0.21 kg Co2 per mile for all flights. This average covers economy, business and first class seats so we need to separate out this average to get a figure for each class of seat.

2 - We've carried out a some research and discovered the following average figures for legroom in each class. We think legroom is the best way of allocating between classes as it's the best, consistently available measure of the space each seat takes up:

Economy - 33 inches
Business - 50 inches
First - 70 inches

3 - We've used the superbly detailed Wikipedia article (dated 7 August 2007) for British Airways to work out the total number of economy (including what they call premium economy), business and first class seats in their entire fleet. Although there are budget carriers that only have economy there are also an increasing number of carriers springing up that only offer business or first class so we believe British Airways is probably a fair representation of the industry average here. We've calculated that British Airways have:

Economy - 45,955 seats = 86%
Business -5,324 seats = 10%
First - 2,400 seats = 4%

4 - This is where it gets a little complicated but we can use these percentages to work out that each class should have the following percentage of the total 0.21 kg Co2 average. You can see how this works by multiplying the percentages above by the percentages below and adding all three together - you should get a total of 1.

Economy - 45,955 seats = 90.80% of 0.21 = 0.1907
Business -5,324 seats = 137.59% of 0.21 = 0.2889
First - 2,400 seats = 192.62% of 0.21 = 0.4045

These are the figures that will be used in the calculations when you choose the class of travel.

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The Wider Impact

Most people now accept that it's not just Carbon Dioxide that we have to worry about when we are flying. Aircraft also pump the following into the atmosphere (source - UK Department for Transport):

 - water vapour (which leads to the formation of contrails and cirrus clouds at altitude);
 - nitric oxide and nitrogen dioxide, together termed NOx (which forms ozone, a greenhouse gas, at altitude);
 - particulates (soot and sulphate particles);
 - other compounds including sulphur oxides, carbon monoxide, hydrocarbons and radicals such as hydroxyl.

And the very fact that the carbon dioxide itself is released into the atmosphere rather than at ground level, as with most other sources, means that it is likely that it has a more concentrated effect on global warming.

So there are other factors to consider that probably mean our Green Debt from flying is worse than the pure Carbon Dioxide produced. Clearly, for the purposes of an accurate calculation such as this the crucial question is just how much worse? Unfortunately there isn't really a consensus on this. The Stern report tells us the following

"The IPCC  [The Intergovernmental Panel on Climate Change] (1999) assumes that the warming effect (radiative forcing) of aviation is 2 to 4 times grater than the effect of the CO2 emissions alone. This could be an overestimate because recent research by Sausen et al (2005) suggests the warming ratio is closer to 2. It could be an underestimate because both estimates exclude the highly uncertain possible warming effects of cirrus clouds."

Cause for concern indeed. For those of us that like flying, a factor of 4 would make flying dwarf all other aspects of our Green Debt. For example, a return flight from London to Sydney would have a Green Debt of over 20 tonnes alone!. However, since 1999 the IPCC have revised their estimate and now a figure of 1.9 is preferred and commonly used.

By checking the 'wider impact' box this factor of 1.9 will be applied to your calculation. We haven't made it automatically part of the calculation as we are not considering the wider of all of the other aspects of our Green Debt so it might distort the figures if this is only considered for flying. On the other hand, there are several reasons why we probably should be ticking the box:

 -  Air travel is still a relatively new contributor to our Green Debt and as such the effects, compared to other sources of carbon dioxide, are still relatively unknown. You may prefer to err on the side of caution and include this factor to add some emphasis to the risk of the unknown dangers of flying in your calculation. 

 -  Compared to the other parts of our Green Debt, the air travel industry is growing at an alarming rate. Unless we reverse this trend soon we will probably do significant damage before we have even had a chance to work out exactly what damage we are doing.

 - Of all the areas of our Green Debt this is one area where the 'financial debt' (the cost of flying) is significantly less than the true cost. Unfortunately, despite the dangers, local governments are often all too keen to boost their economies by offering subsidies to entice airlines to land there, which is why we get our cheap flights. By ticking the box you are recognising that it is important to make up for this market distortion by adding a little extra to your Green Debt.

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Summary

We put all of these pieces together to come up with the following formula to calculate your Green Debt from flying.

Miles travelled one way
+ 125
- (Miles travelled one way * 0.15)
x 2 (if return)
x 'Wider impact' multiplier (1 or 1.9 - your choice)
x Number of passengers
x Number of flights (if it's a regular flight)
x either 0.1907, 0.2889 or 0.4045 depending on whether you fly economy, business or first class.
= your flying debt per flight.

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In 1963 British Rail chairman Dr Richard Beeching decided that we had far too many railways and that it would be sensible to close the vast majority of smaller rural and branch lines. He was right economically, car ownership was taking a grip on Britain and these lines would no longer be used. The ghosts of these lines still haunt our landscape, many now put to good use as footpaths and bridleways, but it's not just the railway romantics that would like to see a comprehensive national rail system make a comeback. If you make a journey by rail instead of by car you'll do a little bit to help stop global warming. The numbers have been crunched and they tell us that the average railway locomotive produces less carbon per person it's transporting than the average car engine. It's even more true for coaches and buses which have also suffered over the last few decades because of our addiction with the motor car.

There is quite a large discrepancy between the Co2 per mile travelled for different types of rail, bus and coach transport. Trains and buses have different types and size of engines for different types of train and journey and the emissions from these different engines need to be split between the number of passengers which, as anyone who has travelled on trains in London can testify, can vary wildly depending on how close to peak periods such as the rush hour your journey is.

It's impossible to consider all of these factors accurately for each journey, but we can come up with a set of averages for different journey types which allow some accuracy. We've used the following sources to establish average Co2 per mile figures:

DEFRA Conversion Factors
Carbon Counter by Mark Lynas (Harper Collins 2007)
How To Live a Low Carbon Life by Chris Goodall (Earth Scan 2007)

These are the average figures (grams per mile)

Mode of Travel	Co2 (grams per mile)
Inter-city rail (2nd class)	0.105
Inter-city rail (1st class)	0.161
Urban rail	0.056
Tube or metro	0.112
City bus or tram	0.048
Rural rail	0.209
Rural bus	0.167
Inter-city coach	0.045
Boat	0.76

The rest of the formula for calculating your Rail, Bus and Boat Debt is pretty self explanatory:

Miles travelled
x conversion factor (see above)
x number of journeys (if regular)
x 2 if return
= Rail, Bus and Boat Debt

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When we think of activities that produce carbon this probably isn't top of our list, but behind the goods and services we buy there are manufacturing processes to power, ships and lorries to fuel, office blocks to heat and light etc.... Whilst it would be fair to say that individually we are not in control of these carbon-generating activities and therefore not responsible, realistically we have to accept that our demand for the outputs is ultimately the cause of their existence.

There are companies out there that are responsible when it comes to their carbon usage, and many more that are desperately trying to become so. We can encourage them. By adding a little 'carbon-awareness' to our shopping habits we can make a difference.

My Green Debt tries to be as accurate as possible, but this is one area where a little estimation is involved. It is simply not practical to work out the Green Debt for each individual product and service that we buy. Instead we ask you to answer a few simple questions and we use these answers to benchmark you against the national average:

- The UK produces just under 600m tonnes of carbon per annum at the moment (DEFRA) and there are just over 60m of us in the country (National Statistics Online). If we use the weighting for under 18's (as set out on the My Profile page) this equates to 54.2m 'adult equivalents. That works out at 11.1 tonnes per person per annum. 

- Roughly half of the UK's carbon is produced by industry and commerce (National Energy Foundation / DEFRA). Of course all of these activities are for the eventual benefit of us as the end consumer, so on average we are each responsible for 5.5 tonnes of carbon through the products and services we buy.

We are not all average but as a starting point for the individual calculation we all need to include an amount for public services and essential industries including health, education, defence, agriculture and public construction. These produce 23% of industry & commerce carbon emissions (Resurgence). Therefore for this calculation we include 1 tonne per person as we all benefit equally from public goods and services.

The remainder of our Green Debt here is estimated by considering the two elements of our consumer behaviour that determine where we sit in comparison to the national average.

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Cars

We've seen cars before and worked out how much driving them around costs the environment, but unfortunately the day we drive it off the forecourt on 5.5 tonnes (for the average car) of carbon has already been emitted in the manufacture and transportation.

Step 1

We estimate how carbon has been emitted in the production of your car(s). We do this for you - using the 5.5 tonne average as a benchmark we use the engine size of your car to rate it against the average. In the vast majority of cases a car with a larger/smaller engine size will weigh more/less and therefore be responsible for more/less carbon in the manufacturing process.

The formula we use for this calculation is

Total carbon from producing a car = engine size (cc) x 0.6 + 4000.

So for a fairly average car (1,800 cc engine size) you'll get an answer of 1,500 x 0.6 + 4000 = 5,480 kg = 5.5 tonnes.

We then divide this figure by two for motorbikes as they are much smaller than cars relative to their engine size. If you have included a % Use figure for this car of less than 100% we'll reduce the total proportionately.

Step 2

As we are getting a picture of your annual carbon output here it is only fair to divide this total over a number of years. We've decided the fairest way to do this calculation is to use the age of your car when you sell it as the number to divide by. This rewards people who buy second hand cars with a lower total and penalises those who regularly buy new vehicles.

Naturally this will involve some estimation - you will have to estimate how long you intend to keep each vehicle. Think about how long you kept your last vehicle and your current circumstances and you should be able to come up with a reasonable estimate.

The average period of car ownership is four years, so this is the default figure for each vehicle.

Your annual total for each vehicle will be the total carbon produced in the manufacture of that vehicle (Step 1) divided by the age of the car when you sell it (Step 2).

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