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Enviromyths

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Motivation

With climate change patterns ever present in the headlines, often the numbers will be skipped over in favour of a more digestible story. Sometimes the environmental benefit is clear cut: putting up the cost of air travel would reduce the number oflights and hence emissions, but what about those benefits which are just too close to call? For example, changing from incandescent light bulbs to compact fluorescent bulbs does save energy on the running costs but ignores the energy involved in their manufacture and subsequent disposal. Would 10 normal lightbulbs be overall better than 1 low energy one? What about in winter when the heat from the bulb reduces the need for central heating?

The following questions are all scenarios that are a bit too close to call. Using some known constants, a bit of estimation, and a few assumptions, maybe there's a quick way to squash some environmental myths?


Can a nuclear power station be carbon neutral?

Question:

Making concrete involves heating up limestone, calcium carbonate, to make calcium oxide used in cement. This liberates carbon dioxide gas. Cement is used as a constituent of concrete used by the construction industry.

Over the running life of a power station, does the saving of CO2 compared with fossil fuelled power stations balance out the vast amount of concrete used to make the power station in the first place?

Illustration

Solution:

The CO2 associated with building the power plant is less than 1% of the equivalent emissions had a gas turbine power station been built instead.

Note, the calculation ignores any emissions associated with running the plant such as workers travel/reprocessing waste/mining Uranium ore. The spreadsheet allows a figure to be added to estimate this.

Download:

Download Excel spreadsheet.

Is it better to scrap an old car or keep driving?

Question:

Steel, plastic, and rubber all come together to produce a motor car. How does the energy embodied in the car through the use of these materials compare with the fuel used when driving the car.

On that basis, is it better to scrap an old inefficient car or just keep on driving it?

Solution:

Seems this is a common thought which was addressed in this Guardian newspaper article. As expected it depends on how many miles are driven typically, the style of driving (motorway, town, etc) and just how old the current car is.

How much forest would soak up CO2 emissions?

Question:

One popular way to counter the guilt of an extravagent purchase is to pay a little extra to have some trees planted in a 'green' tree hugging way.

Given the annual carbon dioxide output from human activities, how many trees would be needed to restore the balance?

Illustration

Solution:

About 24% of the earth's land area would be needed to have enough trees, however only 36% of the earth's surface is suitable for growing things on (the rest being desert or mountains), and we currently need about 24% to grow food on.

Note, the calculation assumes the trees keep on growing forever when in practice for a net removal of CO2 more new trees would be required to counter the rotting wood's emissions.

Download:

Download Excel spreadsheet.

Should I bother cleaning out a used baked bean can?

Question:

With curb side recycling schemes in many towns and cities or recycling points at the local supermarket, everyone is encouraged to recycle packaging wherever possible.

Does the energy to heat the water used to wash out the packaging exceed any benefit?

Illustration

Solution:

It turns out the process of heating the water is dwarfed by the production of the steel used to make the can, even though the can weighs very little. It would be possible to wash out the can more than 8 times and still save energy overall.

Download:

Download Excel spreadsheet.
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