Working Group I: The Scientific Basis

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Appendix VI - Units

SI (Systeme Internationale) Units:

Physical Quantity Name of Unit Symbol
length metre m
mass kilogram kg
time second s
thermodynamic temperature kelvin K
amount of substance mole mol

Fraction Prefix Symbol Multiple Prefix Symbol
10-1 deci d 10 deca da
10-2 centi c 102 hecto h
10-3 milli m 103 kilo k
10-6 micro µ 106 mega M
10-9 nano n 109 giga G
10-12 pico p 1012 tera T
10-15 femto f 1015 peta P

Special Names and Symbols for Certain SI-Derived Units:

Physical Quantity Name of SI Unit Symbol for SI Unit Definition of Unit
force newton N kg m s-2
pressure pascal Pa kg m-1 s-2 (=N m-2)
energy joule J kg m2 s-2
power watt W kg m2 s-3 (=J s-1)
frequency hertz Hz s-1 (cycles per second)

Decimal Fractions and Multiples of SI Units Having Special Names:

Physical Quantity Name of Unit Symbol for Unit Definition of Unit
length Ångstrom Å 10-10 m = 10-8 cm
length micron µm 10-6 m
area hectare ha 104 m2
force dyne dyn 10-5 N
pressure bar bar 105 N m-2 = 105 Pa
pressure millibar mb 102 N m-2 = 1 hPa
mass tonne t 103 kg
mass gram g 10-3 kg
column density Dobson units DU 2.687x1016 molecules cm-2
streamfunction Sverdrup Sv 106 m3 s-1

Non-SI Units:
°C degree Celsius (0 °C = 273 K approximately)
Temperature differences are also given in °C (=K) rather than the more correct form of “Celsius degrees”.
ppmv parts per million (106) by volume
ppbv parts per billion (109) by volume
pptv parts per trillion (1012) by volume
yr year
ky thousands of years
bp before present

The units of mass adopted in this report are generally those which have come into common usage and have deliberately not been harmonised, e.g.,
GtC gigatonnes of carbon (1 GtC = 3.7 Gt carbon dioxide)
PgC petagrams of carbon (1 PgC = 1 GtC)
MtN megatonnes of nitrogen
TgC teragrams of carbon (1 TgC = 1 MtC)
Tg(CH4) teragrams of methane
TgN teragrams of nitrogen
TgS teragrams of sulphur

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