No. 18 Offset your carbon with Inga alley cropping! Part 2
By Tiiu Miller | Newsletter No. 18 March 2010

A rough guide to what you might give.

Should one offset at all? Or not travel? Or what? That's for another day.

We assume you travel and want to offset by supporting Rainforest Saver to promote sustainable farming by Inga alley cropping. This is an alternative to the slash and burn farming which is destroying rainforests. Saving the rainforests is vital for our climate. And Inga alley cropping has the great added benefit of lifting poor farmers out of poverty.



Holiday destinotions

Holiday destinations? Pico Bonito visitor centre by the Cangrejal river, Honduras and North Honduran coast. Photo by Tiiu Miller 2009.

The alley cropping itself cannot, at least without further research, be considered as a carbon sink. The benefit comes from reduction in the loss of rainforest. For a fuller discussion of this see Part 1(1). Here we will consider how much it might be appropriate to give as a carbon offset. (Photo copyright © Tiiu Miller 2009)

Burning forest

Forest burning for slash and burn. Photo by R. Grant 2008.

So how much might you give?

That requires two calculations:

1. How many tonnes of carbon dioxide do you think you are responsible for?

2. What would be an appropriate amount to donate to Rainforest Saver per tonne emitted, and hence for your trip (or other offset)?

Different carbon offset projects vary greatly in their estimates for offsetting the same amount of carbon by using their particular method, from £3 to £14.5 per tonne for the ones considered by Ethical Consumer (2). The cheapest however may not be doing the best job. We recommend Inga alley cropping for its overall benefits.

There are many carbon calculators available, but all are not equally valid. Here are four points to consider:

1. Be clear as to whether you are measuring carbon or carbon dioxide and don't mix them!

A carbon dioxide molecule (CO2) is made up of 1 carbon and two oxygen atoms. Hence I kg of carbon emitted is equal to 3.67 kg CO2. eCO2 means that not just the CO2 but also other greenhouse gases have been included, with all being converted to CO2 equivalents.

2. The absolute amount of carbon emitted by air travel needs to be multiplied by a factor called RFI (the radiative forcing index) to take account of its greater warming effects at high altitudes, but the experts cannot agree as to what this factor should be! It is generally thought to be between two and four, but even seven has been used. The IPCC  (Intergovernmental Panel on Climate Change) uses 2.7 so that might be appropriate. The important point is that we must not just omit this factor.      

This factor is greater for high altitude long distance flights than for short haul, which tend to fly lower. On the other hand taking off and landing add a disproportionate fuel cost to short haul flights.

3. Measurements of quantity are sometimes given in tons (also referred to as short tons), and sometimes in tonnes.

1 tonne (or metric ton) = 1,000 kilograms. (1 kilogram = 1,000 grams or 2.2 pounds)

1 short ton = 0.90718474 tonnes

4. Remember to take account of the number of people travelling. And a return trip is double one way - don't leave yourself in Timbuktu!

Ethical Consumer (2)  has again helpfully assessed carbon calculators, as have some others. Feel free to choose whichever one you like, but the following seem to be well thought of:

Atmosfair was Ethical Consumer's best buy.

But if you want to calculate your emissions really quickly here is a rough and ready calculator for all travel(3). (They have calculators for all other aspects of your life too):

1.  TRANSPORT (in CO2 or CO2 equivalent, not C)Accounts for energy use, non-CO2 exhaust emissions, emissions in car manufacture.

a) Car drivers

For each 1000 miles you drive each year:

If you drive a petrol car using 8.5 litres/100km score: .......................................415kg

For a diesel car using 6.5 litres/100km score ....................................................380kg

For petrol cars if most of your trips are below 3 miles add 25% (extra fuel for cold


If you drive a 4x4 or large people mover add 50% (100% for biggest engines) to

your figure so far but for a small car (e.g. Clio or new Mini), subtract a third.

Divide by the number of people in the car (but don't include those just coming

along for the ride) to get your car score for the year:

b) If you use public transport:

For every 1000 miles/year you travel by bus or diesel train, add .....................  90kg

For every 1000 miles/year by electric intercity train or Underground add ........ 50kg

For every 1000 miles/year by light rail or tram add .......................................... 25kg

c) For each hour you spent flying, short or long haul, in the last year, add .. 350kg

 Your transport score (a+b+c) in kg CO2-equivalent.

You can of course use these figures to calculate for just one journey only, like your holiday trip.

As an example we have looked at a return trip for one person between London Heathrow and Bangkok, Thailand.  Different calculators give different results, but they are not very widely different. I found figures between four and a half to nearly seven tonnes CO2 per person, with an average of about six. We will use six for our examples.

Next, in order to offset this via Rainforest Saver, we need to know how much CO2 there is in a hectare of rainforest. That depends on the type of forest.  Figures range from 147 tonnes per hectare for a new plantation of palm oil (but that is not rainforest) to logged over forest with 256 to 734(4), to 1468 tonnes in untouched forest, and even as much as 2844 in some very old dense forests in Australia, though the latter figure is for both above- and below-ground biomass(5). An average of 628 tonnes (171 t C) has been found for the above ground content for tropical rainforests(5). As these are all approximate figures we will round that to 600 tonnes CO2 per hectare.  So to offset the 6 tonnes released by the trip in our example we need to have a farmer plant one hundredths of a hectare i.e. 100 square metres on his land, rather than slashing and burning that area of rainforest.


Pineapples ripening in Inga alley

Pineapples ripening in Inga alley. Photo by FUPNAPIB 2006.

What is the cost of offsetting one tonne? Or, in our example, what does it cost us to have 100 square metres of land converted to Inga alley cropping?

That is not a simple calculation. The cost of the demonstration plots that are currently being set up is much higher than the later costs will be when many farmers adopt the system. Present costs include seeds, tools and fencing for each farmer as well as the costs of promoting and explaining this new system. That includes costs of publicity, educational materials, hire of a place for teaching and demonstration, transport, and maybe wages for those trained to help the farmers adopt the system.

Our calculations are based on the project in Cameroon because your money could be used there immediately. Several farmers there are waiting to take up Inga as soon as more money becomes available. Also a lot of slash and burn of both primary and secondary rainforest is practiced in Cameroon. 

At the moment enabling these farmers to take up Inga alley cropping costs us about £21 per tonne. That is, for £21 an area of land can be put to Inga that equals the area of rainforest that contains carbon which, when burned, would have released 1 tonne of CO2.

Inga Class

Class on Inga with Cameroon farmers who are wanting to take up Inga. Photo by Gaston Bityo 2010.

But the same Inga alley plot, once it is established, will replace forest destruction for many years to come.  The Inga plot generally takes 3 years to become fully productive. Carbon offsets should take place in a reasonably small number of years. That is one reason why a lot of tree planting is not suitable, if the tree has to have grown 50 years before it has taken up your emissions. The reduction is needed much sooner.  We reckon 5 years seems like a good time scale, though a bit longer would be acceptable.

So for your £21 after 3 years you will have offset 1 tonne of CO2.  The next 2 years also offset 1 tonne each year, as, if the farmer was still burning the forest he would be burning a new plot each year. So the total in 5 years becomes 3 tonnes. Another way to look at this is to say that to offset 1 tonne with Inga alley cropping within 5 years you need pay not £21 but £7.  So in our example the 6 tonnes of emissions per person would be offset by £42. Don't forget to multiply your figure per person by the number traveling for whom you are doing the offset.

Some possible problens.

Would all the farmers who take up the Inga have really been going to cut and burn rainforest? Perhaps not all. You may have saved the odd family from ending up in the misery of a city slum instead.  Some would burn a new plot every two or even three years rather than every year. That means your offset will take longer, but still not by an excessive amount. Maybe a few have reasonably good land that they would be farming sustainably anyway. It is unlikely that anyone so fortunate would ever bother to learn about the Inga. Would some who try it give up? Maybe, but the experience in other places has been that once a farmer has tried it they are more likely to put more of their land to Inga than to give up.

Against any such possible failures there are two compensations. Firstly productivity with Inga may well be greater than without it, even as much as four times greater according to some figures from Honduras. That would mean that for each hectare of Inga more than one hectare of forest would be saved, as the farmer would need to cultivate less land to grow the same amount of food.  Secondly we are starting a snowball effect. As more farmers see others who are doing it they will try it too. Also the plots will continue for many more years. We expect them to produce indefinitely, probably with the occasional addition of fertilizer like farmyard manure. As the farmers grow their own seed and become expert at the technology the costs will come down dramatically. This however is for the future, not for to-day's carbon offsets, but it does show how very cost effective saving the forests is for reducing climate change.  In contrast when rainforest is cleared for palm oil biofuel the amount of CO2 released vastly exceeds any savings from the burning of renewable fuel(4). It has been suggested that it could take as much as 100 years for that ‘carbon budget' to balance.

Rainforest Pico Bonito

Rainforest, Pico Bonito Park, Honduras. Photo by Tiiu Miller 2009.

In Conclusion

This is all about purely voluntary carbon offsets. Feel free to give whatever seems right to you and what you can afford. We are grateful for all and every donation.   However, if you want to follow our guidance, we suggest that you first work out how many tonnes of CO2 you emitted using the method outlined above.  Then for each tonne of CO2 a reasonable offset to Rainforest Saver would be £7. 

In time our costs will alter. Many farmers will in later years be planting Inga alleys using their own seed and other resources at no cost to Rainforest Saver at all.  Our recommendations will then change accordingly.  But to achieve that we have to pay many costs now, and it is right that to-day's carbon should be offset at to-day's prices.


by the secure PayPal facility, or post your cheque to the address given at Support Us. Thank you very much.


1. Offset your carbon with Inga alley cropping! Part 1

2. Carbon offsets. Enron environmentalism or bridge to the low carbon economy?

3. Copyleft: Laurie Michaelis, Living Witness Project, 7 December 2009. Copying and use unrestricted.

4. "Up for Grabs" EIA/Telepak report 2009 ISBN 0-9540768-8-5