| SI (Système Internationale) units |
| Physical Quantity | Name of Unit | Symbol |
| lengtht | metre | m |
| mass | kilogram | kg |
| time | second | s |
| thermodynamic temperature | kelvin | K |
| Fractions and multiples |
| 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 |
| Non-SI units, quantities and related abbreviations |
| °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” |
| ppm | mixing ratio (as concentration measure of GHGs): parts per million (106) by volume |
| ppb | mixing ratio (as concentration measure of GHGs): parts per billion (109) by volume |
| ppt | mixing ratio (as concentration measure of GHGs): parts per trillion (1012) by volume |
| watt | power or radiant flux; 1 watt = 1 Joule / second = 1 kg m2 / s3 |
| yr | year |
| ky | thousands of years |
| bp | before present |
| GtC | gigatonnes (metric) of carbon |
| GtCO2 | gigatonnes (metric) of carbon dioxide (1 GtC = 3.7 GtCO2) |
| CO2-eq | carbon dioxide-equivalent, used as measure for the emission (generally in GtCO2-eq) or concentration (generally in ppm CO2-eq) of GHGs; see Box “Carbon dioxide-equivalent emissions and concentrations” in Topic 2 for details |