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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