Calculating and Reducing Your Personal Carbon Footprint

How  can  you  calculate  your  own personal carbon footprint ?

The carbon footprint of an object, for instance a car, is the amount of CO2 emitted in the course of it being manufactured. It needs to take into account the carbon footprint of the materials used and the energy inputs at vary stages of its production from the primary source to the point where the finished items are bought. In the case of the car, this involves the energy consumed in recycling the steel, or mining and smelting the iron ore to produce the car. Then, there is the energy required to produce the other materials and components such as the tyres. All are assembled in the car factory, using more energy and the finished car is finally shipped and transported to a showrooms. The total amount of energy required to produce the car, or any item or deliver any service, is termed its Embodied energy.  Needless, to say this can be very difficult, or virtually impossible to calculate in many cases, as all the energy inputs have to be aggregated. For instance, where were the tyres made, how much energy did it take to produce each one and was the electrical energy source green (renewable) or dirty (fossil-fuel generated) ?

Rather than attempting to calculate the carbon footprint of our consumables for the purpose of deciding where and how to reduce our carbon footprint , we can make the process much simpler by adopting the general sustainable lifestyle principles:

  1. Reduce the consumption of a product or service where possible.
  2. Buy products and services that source green and sustainable ingredients or inputs in their manufacture or delivery.
  3. Reuse, repair or re-purpose items to extend their useful lifespan.
  4. Recycle items, if possible, at the end of their lifespan.

However, it is somewhat easier to calculate our carbon footprint in our domestic energy consumption and transportation behaviour. Considering that 73% of global GHG emissions are produced by energy generation, substantial reductions of GHG emissions can be achieved if every individual uses less electricity in the home or travels more energy efficiently.

Calculate you annual carbon footprint:

Domestic Example:

In Ireland the average annual domestic electricity consumption for heating, lighting and appliances is 4,200 kWh.

For Ireland, the electricity in the grid comes from a mixture of renewable sources (43%), mainly wind, and fossil fuels (Gas, Oil, Coal) and Interconnector for the remainder 57%. This means on average each unit of electricity, kWh consumed in Ireland  produces 0.31 Kg CO2e ( this compares to the EU average 0.25 KgCO2e). This carbon footprint of each kWh is termed  the Carbon Intensity, and its varies with each country in Europe (and the world). For example, Sweden which uses hydro and nuclear energy sources for its electricity supply, its carbon intensity is 0.012 Kg CO2e.

Therefore, the electricity carbon footprint of the average Irish household is:

4,200 kWh X 0.31 Kg/kWh CO2e = 1, 302 Kg CO2e = 1.3 Tonnes CO2e.

Reducing the central heating thermostat by 1C in the winter will save about 500 kWh in electricity, approximately €100 in costs and of 150Kg CO2e.

If all 1.2 million family households in Ireland, reduce their thermostats by 1°C  in the winter, Ireland’s GHG emissions would reduce by almost 200,000 Tonnes CO2e per year. A huge saving for the price of wearing a wooly jumper instead of a T-shirt inside your house.

Car Transportation:

The fuel consumption of car depends on its design, weight, number of passengers and the nature of the journey whether it is in a congested stop-start urban or open road scenario. 12 Km per litre is not an unrealistic average value for a petrol car.

In Ireland, the average number of miles driven per year in a privately owned car is 17,000 Km. This mileage will consume approximately 1,400 litres of petrol.

Each litre of petrol produces 2.3Kg  CO2e. Therefore, in a year each car is producing 1,400 L X 2.3 Kgs CO2e/L = 3.2 Tonnes CO2e

How does this compare to an electric car ?

To make a direct comparison we need to take into account two major factors:

  1. Electric cars use electricity(obviously), so their carbon emissions depend on how clean (or green) is the electricity used to charge them.
  2. Electric cars are highly energy efficient. 80% of the energy from the grid charging their batteries is converted into motion. Internal combustion(petrol/diesel) engines, by comparison only convert about 15-30% of their fuel’s energy into motion, the rest is converted into waste heat(the reason you need a radiator in a petrol car to prevent the car seizing up).

In an ideal world where  electricity is carbon-free the emissions are zero for an electric car. However, in Ireland like many other countries in the world

Electric cars only need about a 1/5th of the energy required by a petrol car. The amount of energy in a litre of petrol, the Energy density is 10 kWh/L. Therefore, the total amount of energy consumed by the average car consuming 1,400 L petrol per year is:

1,400 L X 10 kWh/L = 14,000 kWh

An electric car will only require 14.000 kWh/5 = 2,800 kWh per year. Since, an electric car is 80% efficient this demands 2,800/0.8 = 3,500 kWh from the grid.

Since the carbon intensity of each kWh in Ireland is 0.31 KgCO2e, 3,500 kWh will produce 3,500 X 0.31 KgCO2e = 1,085 KgCO2e = 1.1 Tonnes CO2e

Therefore at the moment, kilometre per kilometre,  electric cars produce a third of the emissions compared to conventional internal combustion cars, and if and when Ireland reaches its 2030 climate target of 70% renewable energy in electricity generation, emissions will be a sixth in comparison.

For the greatest reductions in transport GHG reductions, public transport is the best option. Already many vehicles are using carbon-neutral fuels, and plans to make all public transport vehicles zero emitters by 2030 is government policy. Even before this happens, busses, trams and trains are more energy efficient than cars. A tram uses 15 times less energy per person per kilometre compared to a car with one driver.

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