# Carbon calculation examples

## 1. Household wanting to offset emissions for one year

### Calculating household carbon emissions

Julie has used the Household Emissions Calculator that is available online from Enviro-Mark Solutions to calculate her annual emissions from household activities including electricity bills, air travel, vehicle use, and household waste. Her emissions are calculated at 7110 kg CO_{2} per year or 7.1 tCO_{2}. Alternatively, Julie could have used the third button on Tāne’s Tree Trust Carbon Calculator which provides emissions for various activities including annual emissions for a typical household.

### Calculating how many trees to plant

The next step for Julie is to use Tāne’s Tree Trust Carbon Calculator for planted natives.

When using the calculator, it is important to realise that trees take some time from planting before they are large enough to make full use of sunlight, moisture and soil. It is not sensible to expect trees planted today to offset Julie’s annual household emissions immediately. It is better to base all calculations on a period of several decades. In her case, Julie decides to use a 30-year time frame to offset her emissions for one year.

Using the Tane’s Tree Trust Carbon Calculator, Julie chooses the option button: **How many native trees are required to offset my CO _{2} emissions?**

She enters her CO_{2} emissions of 7.1 tonnes, sets the age to 30 years, and uses the default planting mix of 25% trees and 75% shrubs.

The calculator estimates that Julie needs to plant 59 native trees and shrubs to achieve her goal. Of these, approximately 25% or 15 should be native tree species such as totara or kauri, and the remainder can be shrub species.

Note that this planting only offsets emissions from one year of activity. Julie will need to continue planting trees in the future to offset her emissions for subsequent years.

## 2. Household wanting to offset all current and future emissions using a single planting of native trees

### Calculating household carbon emissions

John has used the Household Emissions Calculator that is available online from Enviro-Mark Solutions to calculate his annual emissions from household activities including electricity bills, air travel, vehicle use, and household waste. His emissions are calculated at 7110 kg CO_{2} per year or 7.1 t CO_{2} per year.

### Calculating how many trees to plant

John now uses the Tāne’s Tree Trust Carbon Calculator for planted natives to calculate the number of native trees to plant.

In contrast to Example 1 where Julie only wishes to offset emissions for 1 year, John wishes his household to be fully carbon neutral over the coming years using a single planting of native trees sufficiently large so that annual sequestration by the trees balances his annual emissions.

When using the calculator, it is important to realise that trees take some time from planting before they are large enough to make full use of the sunlight, moisture and soil. It is not sensible to expect trees planted today to offset John’s annual household emissions immediately. Rather, it is better to base all calculations on a period of several decades. In his case, John decides to use a 50-year time frame. He could have used a shorter period (e.g., 25 years) which would have produced quite similar results. However, use of a period less than 25 years would not be advisable because of the time it takes for trees to fully establish.

John calculates his emissions over the next 50 years to be 7.1 tonnes multiplied by 50 or 355 tonnes of carbon dioxide.

Using the Tāne’s Tree Trust Carbon Calculator, John chooses the option button: **How many native trees are required to offset my CO _{2} emissions?**

He enters his CO_{2} emissions over 50 years of 355 tonnes, enters the age of 50 years, and uses the default planting mix of 25% trees and 75% shrubs.

The calculator estimates that John needs to plant 1596 native trees and shrubs to achieve his goal. Of these, approximately 25% or about 400 should be native tree species such as totara or kauri, and the remainder can be shrub species.

In practice, it may be too large a commitment for John to achieve such a large planting in one year. The area of land required for such a planting would be nearly 1 hectare. However, an alternative option would be to spread the planting over several years. For example, if John was able to plant 160 native trees and shrubs per year over the next 10 years, this would achieve the same result over a slightly longer time frame.

## 3. Large corporate wanting to offset emissions

A large New Zealand retail business wants to become carbon neutral and would like to promote the planting of native forestry in New Zealand to offset its annual carbon emissions. While it is actively implementing changes to its operations to reduce emissions, its current annual level of carbon emissions is 23,000 tonnes of CO_{2}.

The company has set a target to become carbon neutral by 2050 through both reducing emissions and planting natives. For its current level of annual emission it requires various scenarios for planting trees to achieve this goal.

As in the previous example, because trees take some years to fully utilise a site after planting, it necessary to base all calculations on a period of several decades. In this case, as the business has a 30-year time frame, it uses a period of 30 years. Annual emissions of 23,000 tonnes per year will total 690,000 tonnes of CO_{2} over 30 years.

Using the Carbon Calculator and the option button: **How many native trees are required to offset my CO _{2} emissions?**

We enter 690,000 tonnes, enter an age of 30 years, and use the default planting mix of 25% trees and 75% shrubs.

The calculator estimates that approximately 5,695,000 trees and shrubs are required to fully offset the business’ emissions over the next 30 years.

Using a recommended stocking of 2,500 trees and shrubs per hectare, this means that nearly 2,280 hectares is required. Rather than planting such a large area immediately, the company could spread its plantings out over several years to achieve the same result over a slightly longer timeframe. For example, if the programme was spread over 10 years, this would require establishing 228 hectares of forest per year.

## 4. Medium sized business wanting to offset emissions

A car company has worked out that their smallest model car produces CO_{2} emissions of 1.5 tonnes based on it being driven 14,000 km per year.

As trees take several decades to begin sequestering carbon efficiently, calculations are based on 30 years. Using the Carbon Calculator and the option button: **How many native trees are required to offset my CO _{2} emissions?**

We enter 1.5 tonnes, enter an age of 30 years, and use the default planting mix of 25% trees and 75% shrubs.

The calculator estimates that to remove 1.5 tonnes of CO_{2} from the atmosphere by age 30 years requires planting 14 native trees and shrubs

## 5. Community planting group wants to know how much carbon their planted forest will sequester

A community group recently planted 1000 natives comprising 750 shrubs and 250 trees. They wish to know how much CO_{2} this planting will remove from the atmosphere over the next 50 years.

They use the option button: **How much CO _{2} will my planted native trees remove from the atmosphere?**

They enter 1000 stems planted, an age of 50 years, and use the default planting mix of 25% trees and 75% shrubs.

The calculator estimates that the planting will remove 222 tonnes of CO_{2} from the atmosphere over the next 50 years.

## 6. Carbon sequestered by a single planted native tree

A family has planted a totara tree and want to know how much CO_{2} it will remove from the atmosphere. As trees take several decades to begin sequestering carbon efficiently, calculations are based on 50 years.

They use the option button: **How much CO _{2} will my planted native trees remove from the atmosphere?**

They enter 1 planted stem, an age of 50 years, and set the planting mix to 100% trees and 0% shrubs.

The calculator indicates that 1 native tree is expected to remove 0.44 tonnes of CO_{2} from the atmosphere after 50 years.

Note that this calculation takes account of the probability that the tree will die before it achieves 50 years. The actual CO_{2} removed from the atmosphere will be higher if the tree survives.

However, it is possible to use the Carbon Calculator to estimate the CO_{2} expected to be removed by a surviving tree at age 50 years. To achieve this, the family can use the button labelled: **I have a measurement from my stand**

They enter 50 years as the age of measurement, a survival of 100%, and leave the other input boxes blank. The calculator tells them that if it survives for 50 years, the tree will be expected to remove 0.63 tonnes of CO_{2} from the atmosphere.

## 7. A farmer has measured a stand of native trees she planted and wishes to know how much carbon they have sequestered

A famer has recently measured a stand of native trees and shrubs she planted 20 years previously. She wishes to know how much CO_{2} they have removed from the atmosphere.

She uses the option button: **How much CO _{2} will my planted native trees remove from the atmosphere?**

As the stand as originally planted contained a mixture of 500 tree species and 500 shrubs, she enters 1000 as the total number of stems planted, and sets the planting mix to 50% trees and 50% shrubs. Because she is interested in the amount of CO_{2} currently sequestered by the stand which is 20 years old, she enters 20 as the stand age.

If the farmer didn’t have a measurement of her stand, she would now have to rely on the generic models in the calculator to estimate the likely sequestration. However, as she has recently measured her trees, she can choose the option: **I have a measurement from my stand**

Her assessment of the stand indicates that 70% of the planted trees have survived to age 20 years, but only 30% of the shrubs are still alive. She measures a sample of trees and assesses their mean height to be 8 m and their mean diameter at breast height to be 14 cm. She does not measure the shrubs but estimates their mean height is about 6 m. She inputs these values into the measurement input boxes, leaving the diameter input box for the shrubs blank. The Calculator estimates that the stand has sequestered 52.0 tonnes of CO_{2} from the atmosphere. She next wishes to estimate how much CO_{2} will be sequestered by the stand at age 40 years. To do this, she changes the age of the estimate to 40 years, leaving the measurement inputs unchanged. The Calculator estimates that the stand will remove 199 tonnes of CO_{2} from the atmosphere by age 40 years.

## 8. A small bus company would like to offset emissions from their fuel consumption by planting native trees

A small bus company uses 11,500 litres of diesel per year and would like to offset its CO_{2} by planting native trees.They want to know how many native trees they would have to plant. Using Google there are websites to work out that 11,500 litres of diesel is equivalent to 30 tonnes CO_{2} (e.g. this website provides a calculator to enter fuel consumption to work out the amount of CO_{2} equivalent emissions).

Using the Tane’s Tree Trust Carbon Calculator, they choose the button: **How many native trees are required to offset my CO2 emissions? **

They enter CO_{2} emissions of 30 tonnes, leave the stand age at the default value of 50 years, and use the default planting mix of 25% trees and 75% shrubs. The calculator estimates to remove 30 tonnes of CO_{2} from the atmosphere by age 50 years, they will need to plant 132 native trees and shrubs to achieve their goal per year. Note that this planting only offsets emissions from one year of fuel consumption. They will need to continue planting trees in the future to offset their annual diesel use for subsequent years.