Someone recently posted to the US Metric Association mailing list a
reference to the EPA's use of 'mt' to apparently mean "metric ton". I
must point out that the SI/metric system does not use abbreviations,
but rather symbols. Symbols are used because of the global scope of
the measurement system. For example: a kilogram is symbolized as 'kg'
everywhere, even China or Russia or Japan. These symbols just happen
to be made of the latin characters that comprise the English alphabet
and so the mistaken assumption that they are abbreviations is often
made by native English speakers.
The SI symbol for ton is simply the lower case latin letter 't'. The
lower case letter 'm' is a prefix meaning "milli-" or one thousandth.
Check this out:
mm : millimeter (1/1000 meter)
mL : milliliter (1/1000 liter)
mg : milligram (1/1000 gram)
mt : milliton (1/1000 ton)
Given that 1000 kilograms (kg) equals 1 metric ton (t), it follows
that 1 mt (milli-ton) equals 1 kilogram.
To me or anyone who knows the SI and understands that "CO2e" means
carbon dioxide equivalent, "mtCO2e" is the same as a kilogram of
carbon dioxide equivalent.
A better way to express 25 000 tons (metric) might be to express it as
grams but with proper prefix scaling with the following in mind (case
is important):
kilo (k) means thousands
mega (M) means millions
giga (G) means billions
25 000 tons = 25 000 000 kilograms = 25 000 000 000 grams => 25
gigagrams (25 Gg).
There is no mistaking the writing of 25 000 metric tons of CO2
equivalent as "25 GgCO2e".
