Measuring Emissions in GtCO~2~

GtCO~2~: Gigatonne of CO~2~ (per year):
- equivalent, 1,000,000,000 metric tonnes.
- We will work with $\approx$ 1–50 GtCO~2~.

Be careful: 1 GtC (carbon) is not 1 GtCO~2~:
- The difference is oxygen.
- 1 tC = 3.5 tCO~2~ .
- Social Cost of Carbon is badly misnamed. The quoted $-figures are really the Social Cost of Carbon-Dioxide (CO~2~).

we hope carbon sinks won’t exhaust.
- e.g., warmer oceans may bubble out more CO~2~
fortunately, no signs of net exhaustion yet
unknown: could also ramp up (e.g., plants)

Long-Lived GHG Emissions

Highly correlated (many even from same sources):

CO~2~ (3/4 of GHG, longest-term).
Methane CH~4~ (1/8 of GHG).
- Much more opaque to IR
- immediate control has big short-term payoffs.
- CH~4~ decays to $\approx$ minute CO~2~.
Other (NOx, CFC).

Global Warming Potential (GWP)

CH~4~ warms more, but doesn’t last as long.
CO~2~: GWP=1.
GtCO~2~e: measure of warming power
We use standard GWP factors.

Factors can be argued with, depending on use case, but good enough for us.

Land Charge

(Human) land charge (per year) is reduced (forest) absorption of CO~2~.
Carbonbrief suggests that the land use charge has declined enough to offset emission increases for about one decade now.
Good news…but needs to be checked.
And how much longer will this be the case?

Water Vapor

Think air humidity.
$\approx$ 3/4 of greenhouse warming.
Not long-lived.
Very responsive to temperature
- Positive feedback amplification.
- Likely fully (100%) driven by long-lived GHGs.
- A scientific minority disagrees (90%?).
but also (mostly) responsible for clouds

World GtCO~2~ Fuel Emissions (Only CO~2~)

From	GtCO~2~
Coal	15
Oil	12
Gas	7
Other	5

Total	38

Methane And NOx: GtCO~2~

From	GtCO~2~e
Cattle	3
Fossil Fuel	3
Rice	1
Fertilizer	1

Total	12

Circle Plot

GHG Sources

From	GtCO~2~e
All = Power, Heat, Agriculture	50
Agriculture	10
Non-Agriculture	40

Combustion	33
Cement	10
Airplanes	2

From	GtCO~2~e
Transport	8
Electricity	14
Heating	4
Industrial	16

Electrifying

Think 25-35 GtCO~2~e is easily electrifiable.
Think 15-25 GtCO~2~e is not (ag, flying, etc.)

Summary

World GHG emissions are huge,
and still accelerating,
- although rate of acceleration (3rd derivative) is slowing.