The Greenfleet Tree Totaller allows you to estimate the amount of greenhouse gas your car usage, household & business fossil fuel use (electricity, gas, etc), and air travel generate each year. The Tree Totaller then calculates the number of trees that need to be planted to offset these emissions, and allows you to pay for the planting of those trees through Greenfleet's planting program.

Remember, these trees will capture this year's emissions over their lives. So you need to pay for more tree planting to offset each year's emissions.

The following outlines the methods and data underlying the calculations in the Tree Totaller.

CAR USE

The section on car use offers several options for calculation of your greenhouse gas emissions.

Method 1 – Australian average emissions

This method applies Greenfleet's traditional approach: each car is assigned a level of annual greenhouse gas emissions equivalent to those emitted by an average Australian car, based on data from the Australian Bureau of Statistics. The data and method used are described in the technical section of the main Greenfleet website.

Method 2 – weekly fuel cost

If you know how much money you spend each week on fuel for your car, and the typical price of fuel, this option calculates how much fuel you use each week (by dividing the weekly cost by the price per unit of fuel), your annual fuel use (by multiplying weekly use by 52 weeks) and, using a standard greenhouse factor per unit of fuel, estimates your annual greenhouse gas emissions. A HELP screen is available to provide guidance if your car uses petrol: it shows typical weekly fuel costs for cars of different classes that travel a range of annual distances. It assumes the price of petrol is $1.50 per litre.

Method 3 – annual distance travelled and vehicle information

If you know the distance (in kilometres) you travel each year and your car's typical fuel consumption (in litres per 100 kilometres), this option calculates your annual fuel use from this information then, using a standard greenhouse factor per unit of fuel, estimates your annual greenhouse gas emissions. If you don't know your car's actual fuel consumption, you can look up the Government website that lists the fuel consumption information for all cars sold in Australia since 1986, and use the City Cycle information in this calculator. Look up www.greenhouse.gov.au/fuellablel then select Fuel Consumption Guide and then select Simple Search. Enter the year, make and model of your car in the boxes, and it should tell you your car's standard fuel consumption. As an alternative, a HELP screen in the Tree Totaller offers you options for a range of types of vehicle and distances travelled, and you can select one of these if your car runs on petrol. A standard greenhouse factor for your fuel is then used to calculate your annual greenhouse gas emissions.

Method 4 – annual fuel consumed

If you know how many litres of fuel you use in a year, this method will directly calculate your annual greenhouse gas emissions using a standard greenhouse factor for your selected fuel. A HELP screen is provided to show how much fuel cars of different classes travelling a range of annual distances would consume when using petrol. You can estimate a number using this information.

UTILITIES

The Utilities section assesses your use of fossil fuels (gas, oil, etc) and electricity generated from fossil fuels – greenhouse gases from electricity are generated at the power station, not at your home or workplace.

We haven't included greenhouse gas emissions from wood usage because wood is a renewable fuel, not a fossil fuel. It's very difficult to estimate the greenhouse gas emissions from using wood without knowing the exact circumstances. Under ideal conditions of sustainable wood use (that is, trees are planted to replace those used as fuel) and efficient burning, the quantity of greenhouse gas emissions absorbed by re-growing trees almost cancels out the emission from burning the wood. However, if wood is sourced unsustainably (for example, by clearing land) or is burned in poorly designed and/or managed heaters (for example, green or wet wood burnt in an open fire or even some wood heaters), greenhouse gas emissions can be higher than using fossil fuels or electricity for heating. What's more, wood heating can be a major contributor to local air pollution, and inappropriate timber harvesting can deprive native animals and plant of habitat, such as rotting logs and nesting hollows.

This calculator estimates your usage of each fuel (see below for the various methods), then multiplies that usage by greenhouse factors from the National Greenhouse Accounts Factors (January 2008), issued by the federal Department of Climate Change. These factors take into account all of the emissions from the raw fuel in the ground to final use of the energy in your home or workplace.

In the first screen, for each energy source you use, you simply select one of the three options:

• I don't use this fuel
• I want to select a typical value
• I want to enter energy bills

You can select different options for different fuels – for example, you can select ‘typical value' for your gas use, and ‘enter bills' for your electricity.

The first option means this fuel will not be included in the calculations.

The second option means you will be asked some basic questions about your location (postcode), the number of people in the home, and the types of fuels used for home heating and hot water. This information is used to calculate an estimate of your usage of the selected fuel. This method gives a rough estimate energy use and greenhouse gas emissions of a typical household with the number of people specified in a climate based on your Postcode location and with the mix of appliances chosen.

We have used Australian Bureau of Statistics and other data on energy use and greenhouse gas emissions of households in different regions to develop formulas to take into account the number of people, local climatic conditions, and types of major appliances. However, the outcome is only approximate, as many additional factors, such as ownership of other appliances and equipment, size of home, how often people are home, how carefully people use appliances, and design of home affect the actual level of energy use and greenhouse gas emissions. But this approach is more accurate than just applying a single average value.

The third option takes you to a screen where you can enter the information from your energy bills for the selected fuel. This is the method you should use as a business or for a more accurate calculation of household energy consumption. Energy bills from different suppliers include different information, so the data entry screen allows you to enter either the average daily consumption in each billing period (often shown on a bar graph on the bill) or the total consumption for each billing period. You must also enter how many days are in each billing period – although usually this is roughly 60 or 90 days. For electricity, you can separately enter your general electricity usage and your off-peak electricity usage (often used for hot water services and some heaters).

Many energy suppliers include a bar graph on each bill that shows daily consumption for each billing period over the past year, plus the last billing period in the previous year. If so, you only need your most recent bill. Otherwise, you need your past years' bills.

If you don't have the necessary energy bills, try ringing your energy supplier(s) account inquiries number. They will normally tell you your consumption in each billing period for the past year if you provide evidence that it is your account.

If you don't have every bill, you may be able to estimate your usage in the missing periods by subtracting the final energy reading on the previous bill from the starting reading on the bill after the missing one. Alternatively, you may be able to make a reasonable estimate of the missing consumption, remembering that the highest bill usually comes in July or August (because of winter heating), and the lowest bill is in summer (unless you do a lot of airconditioning).

If you use this approach, we simply add up the total amount of each energy source used over a year, then multiply it by the appropriate greenhouse factor. If the number of days in the billing periods entered doesn't add up to roughly a year, you will be given the option of editing the billing data or the calculator will adjust your usage to the equivalent of a year. For example, if you entered billing data for 400 days, the total consumption would be multiplied by 0.91 to adjust it back to a 365 day year.

AIR TRAVEL

The air travel section allows you to estimate domestic (within Australia) and international air travel.

You can choose a simple approach (option 1), or make more detailed estimates (Option 2)

In each case, you can enter one or more trips, and they can be one way, return or multiple destination trips.

Direct or full impacts?

You can choose to offset just the direct greenhouse gas emissions from your air travel, or the full global warming impact of your travel, which is much higher – at least 2.5 times greater. The direct greenhouse gas emissions include the impacts that are included in international agreements such as the Kyoto Protocol, mainly carbon dioxide from burning fuel. However, when aircraft release emissions high in the sky, they also create some indirect impacts that increase global warming. For example, the contrails (cloudy trails) left behind trap more heat in the atmosphere. Also, release of some greenhouse gases high in the atmosphere has a greater impact than if those same gases were released at ground level, as some of the gases released at ground level would not reach the upper atmosphere. Estimates of the full impact are still very uncertain. The Intergovernmental panel on Climate Change has published a detailed paper on this issue (go to www.ipcc.ch then select ‘publications' then select ‘special reports' and you can download the summary of Aviation and the Global Atmosphere, 1999) and has estimated the possible range as 2.5 to 7 times as much as the direct impact. We have used the lower end of this range (2.7) for this calculator, so the actual impact may be even greater than this calculator estimates.

So, if you want to cover the basic emissions generated by burning of the fuel, select the ‘direct impact' option. If you want to take responsibility for the greater impact caused by releasing these emissions high in the atmosphere, select the ‘full impact' option.

Option 1 – average trip length

• This simple approach applies an average trip length to each trip, then calculates the greenhouse gas emissions from that. Three different typical trip lengths are offered:
• an average Australian trip of about 1100 kilometres. This distance is the average for Australian air trips based on data from AVFACTS published by the Bureau of Transport and Regional Economics
• a typical short international trip (around 6,300 kilometres) estimated from AVFACTS data. It is the average of a sample of trips to a number of Asian capital cities from eastern Australia
• a typical long international trip (around 14,000 kilometres) to the USA, UK or Europe.

You simply enter the number of each type of trip you want to include, and the calculator estimates your greenhouse gas emissions.

Option 2 – calculate actual trip distances

In this approach, you enter the departure point and destination for each trip (and whether it is one way or return). This can be done in either of two ways:

• type in the names of the starting point and destination – the program will try to guess the full name, but if it's wrong, just keep typing
• use the maps (separate maps for flights within Australia or international flights) and the mouse to select the starting point and destination of each trip

Each trip can be a single trip, a return trip, or a multi-destination trip (up to 9 locations). The calculator can add up all your trips. You can look at the list of trips and edit or delete trips if you wish.

Once you've finished, the calculator will estimate the greenhouse gas emissions from all of your air travel.

HOW IT WORKS

The calculator includes estimates of the greenhouse gas emissions per passenger-kilometre for typical aircraft flying on domestic or international routes at average occupancies. The extra fuel used for taxiing, take-offs and landings is also taken into account. Data were collected from various sources including AVFACTS published by the Bureau of Transport and Regional Economics, as well as websites of a number of airlines, including British Airways and Qantas and a number of articles and papers in which estimates of greenhouse gas emissions from air travel have been estimated.

For each trip, it is assumed that the aircraft travels a Great Circle route (the shortest distance between two points on the Earth's surface) and cruises at around 10,000 metres altitude.

Calculating the number of trees per tonne of carbon dioxide...

Greenfleet has published its approach to estimating the number of trees per tonne of carbon dioxide offset in the technical section of the main website, under 'Transport and the Environment'.