Since 1976 humans have increased the CO₂ concentration 27% from 330ppm to 420ppm by emitting 100 times more CO₂ than all the world's volcanoes combined. phys.org/news/2019-10-h…
Since the Industrial Revolution humans have increased the CO₂ concentration 50% from 280ppm to 420ppm.
Humans are now responsible for 33% of the atmosphere's CO₂.
Length:
Very few professionals say "centimetres" as it's a bit of a mouthful. Most will will use millimetres and say "mill" so instead of "12.5 centimetres" they will say "125 mill".
As for kilometres...
it's not pronounced keelometres but kill-ometers - same goes for kilograms. Most people say "5 k" - weirdos say "5 clicks"
Weights:
Grams is grams. Simple.
Kilograms is just "k g" so for example: "5 and a half k g"
Aside: Why the hell do americans say "13,200 pounds" when you've got a decent other unit of tons which is pretty close to a metric tonne? Do better!