measurement

Introduction

In this section we would like to provide some explanation our approach to carbon calculations.

The calculations are essentially divided into two halves.

On one hand we have the carbon emission calculations, in which we assess the carbon footprint of our partner, whether an individual or an organisation.

On the other hand we have the carbon sequestration calculations, in which we derive the amount of carbon that is taken up by our tropical trees.

Both of these calculations are essentially straightforward, but contain some critical areas from where huge inaccuracies can arise.

If you were to ask a hundred offsetting companies to assess your carbon footprint, you would get a wide range of answers. We should fall reassuringly into the middle of that range.

We urge you to avoid the extremes, where companies are far too cheap or far too expensive, (as explained in our article entitled Tripwires).

Carbon emissions calculations

In all starts with an assessment of your carbon footprint.

For individuals who want to offset either their whole lifestyles or specific purchases like trips or products, we have pre-calculated examples with specific offset packages, which are almost always suitable for being purchased off-the-shelf, there is rarely a need for us to run a bespoke carbon calculation.

The most complicated part of these calculations is deciding what to include and what not to include. For example, the carbon cost of a car should clearly include its manufacture and maintenance (amortised across its lifespan), as well as its fuel consumption. But should it include the carbon cost of the roads that we drive on?

You can discover more about how we reach our solutions on the pages for each specific offset.

For organisations there are usually two distinct carbon footprints that need to be considered, that of the company infrastructure (indirect costs) and that of the products (direct costs).

We need to assess and calculate both of these numbers before we are able to provide you with a firm quotation for carbon offsetting. However, we do have templates set up for most business scenarios, so isn’t usually a particularly complex of extended process.

The infrastructure footprint is usually offset by the payment of an annual fee, whilst the offsetting for the product footprint only becomes payable as you make each individual sale.

The most complicated areas of these calculations tends to be drawing the line between which carbon overheads fall into infrastructure and which into product (which can make a huge difference to certification costs) and the sticky question of where it is appropriate to amortise carbon debts over multiple years (notably for buildings).

Please refer to the pages for each business sector, which are linked from the introduction page for organisations.

Carbon sequestration calculations

When we talk about carbon sequestration calculations, what we are essentially trying to determine is how much carbon our tropical trees absorb each year through photosynthesis.

This might seem like quite a simple question, but it’s actually quite a difficult one to answer with confidence.

If you take a mature tree, cut it down, gather all its component parts (trunk, branches, leaves and roots), dry them out in an oven and then weigh them, you will get a pretty good approximation of how much carbon that tree has sequestered over its lifespan.

Of course you can’t go cutting down every tree to do these measurements, so instead allometric regression modelling is commonly used. In this technique the data from our sacrificed trees is used to create equations that relate easy-to-measure variables (height, diameter) to carbon content. Those equations are then used to estimate the carbon content for similar trees..

Unfortunately this technique is notorious unreliable, due to the vast variances between trees of the same species (largely due to their immediate situation, shade, competition, soil conditions, pests etc.). Additionally, equations are very rarely available for the species and locations of interest.

The other major problem is that trees do not sequester carbon at a linear rate.

For the first part of their lives (10-20 in the tropics, 50-100 years in temperate zones and 80-120 years in boreal forests) they are primarily focused on upward growth, during which they remain spindly and not very good at absorbing carbon. Almost all trees then reach a point called the Critical Age, where they suddenly ease off from upward growth and start their adulthood, during which they put on substantial mass, which actually increases every year until they die, 100-4000 years later.

In other words, only trees planted in the tropics have any chance of growing fast enough to have an impact on climate change over a reasonable timescale.

We started planting our trees in 2009, so we now have many specimens which around the Critical Age and entering their productive age from a sequestration point of view. We use these mature trees for offsetting purposes, while deploying your payment towards plant new saplings.

When it comes to determining how many trees we need to plant to offset your carbon footprint, we use a value of 25 kgC per tree per year, which we derive using the practical modelling technique developed in the pioneering paper “The relative efficiency of carbon sequestration for tree plantations in different parts of the world”.

Our observation is that our mature trees put on substantially more timber than that each year, but we prefer to be on the safe side, to enable us to include less mature trees as our projects expand.