Thing measured | unit name | symbol | value |
---|---|---|---|
humans | person | p | |
mass | ton | t | 1 t = 1000 kg |
gigaton | Gt | 1 Gt = 10^{9} × 1000 kg = 1 Pg | |
transport | person-kilometre | p-km | |
transport | ton-kilometre | t-km | |
volume | litre | l | 1 l = 0.001 m^{3} |
area | square kilometre | sq km, km^{2} | 1 sq km = 10^{6} m^{2} |
hectare | ha | 1 ha = 10^{4} m^{2} | |
Wales | 1 Wales = 21 000 km^{2} | ||
London (Greater London) | 1 London = 1580 km^{2} | ||
energy | Dinorwig | 1 Dinorwig = 9 GWh |
Throughout this book “a billion” (1 bn) means a standard American billion,
that is, 10^{9}, or a thousand million. A trillion is 10^{12}. The standard prefix
meaning “billion” (10^{9}) is “giga.”
In continental Europe, the abbreviations Mio and Mrd denote a million
and billion respectively. Mrd is short for milliard, which means 10^{9}.
The abbreviation m is often used to mean million, but this abbreviation
is incompatible with the SI – think of mg (milligram) for example. So I
don’t use m to mean million. Where some people use m, I replace it by M.
For example, I use Mtoe for million tons of oil equivalent, and MtCO_{2} for
million tons of CO_{2}.
There’s a whole bunch of commonly used units that are annoying for various
reasons. I’ve figured out what some of them mean. I list them here,
to help you translate the media stories you read.
The “home” is commonly used when describing the power of renewable
facilities. For example, “The £300 million Whitelee wind farm’s 140 turbines
will generate 322 MW – enough to power 200 000 homes.” The
“home” is defined by the BritishWind Energy Association to be a power of
4700 kWh per year [www.bwea.com/ukwed/operational.asp]. That’s 0.54 kW,
or 13 kWh per day. (A few other organizations use 4000 kWh/y per household.)
The “home” annoys me because I worry that people confuse it with the
total power consumption of the occupants of a home – but the latter is actually