The One Tonne Life project has ended and the content on this web page is static and is not updated any more. The project was unique and pioneering, making the conclusions and all information connected to the project just as interesting and up-to-date today as when it was run. Read more about the project and get inspired! (March 2017)

One Tonne Life

Tag: Fredrik Hedenus

Chalmers offers tips to the family

The “Robinson” phase of One Tonne Life means that the family is making a huge effort to get close to the target of one tonne of carbon dioxide per person per year. Fredrik Hedenus and Anna Björk from the Chalmers University of Technology, who have been calculating the family’s carbon dioxide footprint from the very outset, put their heads together and wrote an open letter to the family and included a number of tips and suggestions – and we know that the family have already adopted several of the two experts’ suggestions:

“Hi Alicja, Nils, Hannah and Jonathan!

Today, eating out accounts for a relatively large proportion of emissions in the “food” category. If everyone in the family chooses vegetarian meals at work and at school, emissions from this category can be reduced to 0.3 tonnes of CO2 equivalent per person and year. Previous weeks with mixed dishes for lunch have put greenhouse gas emissions between 0.6 and 0.8 tonnes CO2 equivalent per person and year. Taking a lunch box from home is one way of further cutting emissions; just how much you reduce emissions depends on what your lunch box contains. Both Fredrik and ICA have offered suggestions for healthy and nutritious vegetarian meals on

Meat and dairy products currently also account for a large proportion of your total emissions. If you abstain entirely from meat, you can reduce your emissions by 0.2-0.8 tonnes CO2 equivalent per person and year, which corresponds to the emissions from previous weeks. By replacing dairy products with oats and soya-based alternatives, emissions can be cut still further. For instance, one litre of regular dairy milk produces emissions corresponding to 1.5 kg CO2 equivalent compared with one litre of oats-based grain milk which only produces 0.3 kg CO2 equivalent.

Driving an electric car or cycling instead of taking the bus is a good alternative since the bus currently accounts for about 0.05 tonnes CO2 equivalent per person and year out of the approximately 0.2 tonnes of greenhouse gases for the travel category. If instead this distance were to be covered by bicycle, emissions would be zero and if driven in the electric car, there will only be a small increase since the car is recharged with electricity produced from hydropower. The metro is still a good alternative since it produces low emissions, 0.7 grams CO2 equivalent/person km compared with the bus which gives 27 grams/person km.

Emissions from furniture production are shown in the “Other” category, as part of the “rucksack”. You can choose to do without certain items of furniture, and emissions will decrease proportionately with the amount of furniture the family can do without. At present, emissions for the household’s total complement of furniture are 0.3 tonnes per person and year. If you can do without one-fifth of the furniture in your home, emissions can be cut by about 0.05 tonnes.
Recreational activities currently account for 0.1 tonnes CO2 equivalent per person and year. In order to get rid of emissions from this category, you will have to decline indoor activities.

Good luck!

Anna Björk & Fredrik Hedenus”

Aviation’s climate impact

Aviation is often seen as a major source of greenhouse gas emissions. And it is true that as a private individual, flying is the single most climate-impacting activity you can undertake (if we disregard space travel). Having said that, we don’t fly all that often, and most people in the world never fly at all. From the global perspective, aviation accounts for only about 2% of total carbon dioxide emissions.

Last week an estimate was made of how much carbon dioxide the family saved by not flying to Switzerland for a skiing holiday. However, the real difference is actually less than the figures given in last week’s presentation. That’s because it is rather difficult to calculate exactly how much climate impact a flight causes. The amount of energy needed to fly one person over a distance of one kilometre depends to a considerable extent on the total length of the flight. Flying from Göteborg to Stockholm requires almost twice as much fuel per kilometre than flying to Beijing, for instance. And of course another vital parameter is how full the aircraft is.

The calculation only takes into account the CO2 emitted during the flight itself, but producing the fuel also requires energy. To this should be added the fact that airports and their various peripheral activities also cause emissions, but these emissions are seldom taken into account when calculating aviation’s total climate impact.

What is most complicated with aviation, however, is the warming caused by aviation apart from the carbon dioxide effect. For one thing, aircraft produce nitric oxide emissions. Nitric oxides have both a warming and a cooling effect on the climate. Warming comes from the fact that they help create ozone. When we talk about ozone we usually refer to the ozone layer in the stratosphere that prevents the sun’s ultraviolet (UV) light from penetrating through to the earth’s surface. However, ozone that is formed at lower altitudes in the atmosphere functions as a greenhouse gas. Furthermore, nitric oxides are also part of a process that breaks down methane, which is a greenhouse gas. If we take all these effects into account over a hundred-year perspective, nitric oxides from aviation will have a slight overall warming effect.

Aviation also causes contrails (also known as vapour trails, seen as white streaks in the sky). The density of these contrailsvaries with factors such as the aircraft’s altitude and ambient temperature. Just how much warming effect this has depends on whether you are flying at night or during the day, and whether the ground below is dark or light.

If we add together the effects of nitrogen oxides and vapour trails, we find that aviation causes an overall warming effect that is about 30% higher than that caused solely by carbon dioxide over a hundred-year period. This time perspective is important: carbon dioxide remains in the atmosphere for a very long time. Ozone remains for weeks, while contrails disappear after a few hours. However, while they are present, they have a significant warming effect. If we were to examine this comparison on a shorter time frame, we would have to increase aviation’s emissions by more than 30%.

To this should be added that contrails can later turn into more long-lasting cirrus clouds high up in the atmosphere. These clouds cause a rise in temperature down on the surface of the earth, although there is some uncertainty as to the extent to which these clouds are caused by aviation. If we also take these clouds into account, the warming effect of aviation is about 70% higher than that caused solely by carbon dioxide. But there are large uncertainties present.

If we now try to calculate the family’s trip to Geneva, the journey is 1680 km long, and flights of that length require about 0.40 kWh fuel per person-km. If we examine aviation fuel from a lifecycle perspective but disregard emissions from airport operations, we end up with 410 kg CO2/person for a return trip. If we now add in the effect of nitric oxides and contrails, the final figure is between 530 kg CO2 eq/person and 700 kg CO2 eq/person.

Emissions per km for the flight are about 158 g CO2 eq/km, which is comparable with doing the trip alone in a large car.

Fredrik Hedenus, Chalmers

Climate targets and 1 tonne

One might well ask how the One Tonne Life project came to the conclusion that it is OK to release one tonne of carbon dioxide equivalents per person and year. After all, the project could have picked a different figure. The answer lies in the fact that there are three main considerations determining the extent of emissions we could have here in Sweden without “destroying” the climate.

The first consideration is just what extent of climate change we feel is acceptable. Many of the world’s nations have backed the 2-degree target, that is to say that the global average temperature may not increase by more than 2 degrees over pre-industrial levels. This means the time before mankind started burning fossil fuels, around 1750. To date the global average temperature has already increased by about 0.7 degrees from that base-line. However, the 2-degree target is not a scientific limit, it is actually a political decision. There are experts who suggest we should impose a 1.5-degree limit instead, and others who say that a higher temperature increase would not cause major problems.

The second consideration is how the climate will respond to a higher concentration of greenhouse gases in the atmosphere. This is a scientific issue, but science does not yet have a clear answer. The climate system is highly complex and it has been a couple of million years since the last time Earth experienced the high levels of greenhouse gases we are seeing today. For this reason we do not really know what is likely to happen. Climate sensitivity is a measure we use to estimate how responsive the planet’s climate is to certain factors. It is expressed as the temperature increase that we will have in the long term if the carbon dioxide concentration of Earth’s atmosphere is doubled over pre-industrial levels. Scientific literature indicates that climate sensitivity is probably between 1.5 and 4.5 degrees.

The third consideration is how many people will be living on Earth and how our emissions are distributed. We believe that the planet’s population will stabilise at about 10 billion around the year 2050, but will everyone be producing the same amount of emissions? At present, the average American produces about 20 times the emissions of the average Indian. Does this mean that the American will be allowed to emit more than the Indian in 2050 too, or that by then it will be India’s time to release more per head of population than the USA? Once again a question that science cannot answer but that is instead a political issue.

Using the Chalmers Climate Calculator (CCC) it is possible to see what emission reductions are going to be needed in order to meet various climate targets. Go to CCC and under Emission Scenario enter the year 2010. After that, at Rate of Reduction write 2. Now press the Generate Scenario button. The graph on the left will show that emissions towards the end of the century will be about 10 billion tonnes of carbon dioxide, so if we have a world population of 10 billion people that means emissions of roughly 1 tonne of carbon dioxide per person and year. The graphic on the far left shows that the global average temperature will have increased by less than 2 degrees. This is a rough explanation of how the target figure in One Tonne Life was decided.

However, if you now key in that Climate Sensitivity is instead 4.5 degrees, and press the Generate Scenario button once more, you will see that the temperature will rise by more than 2 degrees. Use this tool to test by how much emissions will now have to be reduced to meet the 2-degree target.

Fredrik Hedenus, Chalmers University of Technology

Latest videos from the project

See all videos on Youtube

Latest photos from the project

Follow us on Facebook
Follow us on twitter