Carbon Footprint of a Mobile Phone

In my on going quest to figure out the environmental impact of every product that I purchase, today I look at cellphones.

After reading this TreeHugger post, I became aware of the LCA of the Mobile Communication System UMTS report which I found at the ESU Services website. This is an excellent report on the energy used and environmental impact of mobile phones, looking at the entire mobile phone infrastructure. I decided to do some further analysis from their numbers to determine the energy use and carbon footprint of manufacturing a mobile phone as well as using it for a year.

How much energy and emissions does manufacturing a mobile phone cause?

Manufacturing a cellphone uses approximately 1390 MJ of energy and produces 60 kg of CO2 emissions (see calculations below).

To put this in perspective, a gallon of gasoline has 131 MJ of energy and emits 8.8 kg of CO2. Therefore, manufacturing a cellphone uses as much energy as 10.5 gallons of gasoline and emits as much as 6.8 gallons of gasoline (energy is higher than emissions due to fossil free electricity from sources such as hydro and nuclear).

A computer and monitor take 6400 MJ to manufacture, or 4.6 times as much as a mobile phone.

The 1.019 billion phones produced in 2006 create approximately 60 million metric tons of CO2 emissions.


What is the impact of using a cell phone for a year?

According to the report, using a cellphone for a year on average uses 4,221 MJ of energy (equivalent to 32 gallons of gasoline) and emits 112 kg of CO2 (equivalent to 12.8 gallons of gasoline). These values take into account the entire system and all the energy and materials needed to manufacture and run it: the phones, base stations, switching system, cable system, and administration. It assumes that each phone is used for one year and then replaced.

To put that in perspective, the average American emits 22 metric tonnes of CO2, so 112 kg works out to .5% of that total. The average American eats 150 hamburgers leading to 600 kg of emissions, so mobile phone usage is about 1/5 of that.


What causes the largest environmental impact in the mobile phone system, and what is the best way to reduce it?

Based on the Hierarchist Eco-Indicator'99 method (whatever that is), looking at the entire system, the mobile phone makes up 50% of the impact, the cell antennas 5%, cell base stations 25%, switching system 3%, administration 14%, connection network 3%. Of the phone's impact, 95% is caused by manufacturing and 5% by usage. So, the key environmental impact is caused by the manufacturing of cellphones.

Looking at that manufacturing:

The production of printed wiring boards (PWB) and integrated circuits (IC) make up about 40–50% of the environmental impacts. For these components, the energy consumption, the production of semiconductor dies, and the supply of gold and partly silver is of importance for the assessment.

Just like computers the integrated circuits and printed wiring boards have the largest impact on the process. Even though the weight of the final product of PWB and IC are small, the amount of raw materials, energy required to manipulated those materials and waste is quite large.

More environmentally friendly ways of production or improvements in the efficiency of their production would have a big effect on the overall environmental impact of cell phone usage. Another way to have reduced impact is to use each phone longer.

Increasing service life from one year to four years would decrease the environmental impacts of about 40%. On the contrary, a life time of only half a year results in about 40% more impacts.

I calculate that replacing a cellphone every 2 years rather than one would save 30 kg of CO2 emissions (about 3.3 gallons worth) and 700 MJ. This is a decent savings, approximately equal to reducing your driving 100 miles each year (8 miles a month). If you are trying to decrease your carbon footprint, this will have an impact, but there are other areas that would make a much larger impact.

Surprisingly, whether the phone is recycled or incinerated has little effect on the overall environmental impact.

Despite the fact that a relatively pessimistic scenario for the disposal was selected (incineration of 20% and 80% take back, instead of 100% take back), the environmental impacts for this life cycle phase can be neglected.

Even a take back rate of 0% would not significantly change the environmental impact.


Calculations

From Table 6 in the report, we find that transferring 1 Gbit in a UMTS system uses 801 MJ of non-renewable energy, 138 MJ of renewable energy and 27 kg of CO2 equivalent emissions. From Figure 6 in the report, I estimate that phones use 35% of non-renewable energy, 20% of renewable energy and 50% of emissions. Multiplying that out, phone usage for 1 Gbit is: 280 MJ of non-renewable energy, 28 MJ of renewable energy and 13 kg of emissions. From this report we find that 0.223 cell phones per GBit, which means 4.5 GBit per cell phone (which is used during 12 months). And no I don't speak German, but Rolf Frischknecht was kind enough to email me the information. So multiplying our values by 4.5 we get 1260 MJ of non-renewable energy, 126 MJ of renewable energy (or 1386 MJ combined) and 58.5 kg of emissions per phone.

Besides manufacturing the phone, this value also includes running it for a year. The report does not spell out what percentage of energy or emissions are used in this phase, but it does say that:

The use of the phone is responsible only for approximately 5% of a UMTS phone's environmental impacts.

I am not sure if the value for energy and emissions is similar, and for the purposes of this analysis will ignore it. Possibly I should reduce the values by 5%, but I would be extremely happy if these calculations were accurate with 25%, so I am not too concerned with it.

For the entire impact of one mobile phone user on the system for one year, we take the 801 MJ of non-renewable energy, 138 MJ of renewable energy and 27 kg of CO2 equivalent emissions per Gbit and multiply it by the 4.5 GBit per year to get 3605+ 621 = 4226 MJ and 112.5 kg.

Assumptions and potential issues

As always, the analysis is only as good as the underlying numbers and the assumptions they hold.

It is not specified what type of phone is being used, or whether it is a generic aggregate of many phones. It is also unclear how much variation in energy use and environmental impact there is between phones.

This is based on the UMTS cellphone protocol. Different protocols could use more energy and have a larger environmental impact.

The data is based on manufacturing the phone in Germany and using it in Switzerland. If the source of fuel to generate electricity is different than assumed this will impact the final results.

Phone usage is assumed to be 4.5 Gbit a year. Greater usage would increase the energy needed to use the mobile phone but also decrease the relative impact of phone manufacturing.