# 2.1 Carbon emissions

A particular concern of green computing is the carbon footprint arising from the energy demands of computing. As you saw earlier, one of the claimed environmentally friendly benefits for cloud computing is that it reduces your carbon footprint because you only use the services when you need them. You can share the computing resources as you don’t need them all of the time. While that may be true, it is also important to know what powers cloud computing’s data centres.

Greenpeace produce a regular report that gives IT companies a mark for their commitment to green energy. Figure 2 shows the entry for Amazon in 2017, which records that they received a ‘could do better’ grade of C. This is not only based on the mix of energy sources they are using (17% renewable, 30% coal, 24% natural gas and 26% nuclear energy), but also on factors such as how transparent they are about their energy use, their commitment to renewable energy sources and their overall efficiency in terms of total energy consumption and reducing greenhouse gas emissions.

Figure 2 The proportion of different energy sources used by Amazon Web Services.

There are many other factors to take into account with data centres energy efficiency beyond how much energy they consume and where the energy comes from. You can read find out more for yourself about this topic, such as the importance of keeping the large number of servers and telecoms equipment cool. Here are two useful search terms that you may not think of: ‘power usage effectiveness’ and ‘water usage effectiveness’.

## Box 1

Power Usage Effectiveness (PUE) is the ratio of the total amount of energy used by a computer data centre facility to the energy delivered to computing equipment. A high PUE indicates that a large proportion of the power supplied to the data centre is being used for non-computational purposes, such as cooling and lighting, rather than being used directly to power the IT equipment.

Water Usage Effectiveness (WUE) is the ratio of the annual water consumption (in litres) to the energy delivered to computing equipment (in kWh). The higher the WUE value, the more water is needed in order to cool the IT equipment, and the less efficient the data centre is in terms of water usage.

Finally in this section, the discussion will be brought closer to home.

OpenLearn - An introduction to computers and computer systems
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