Measuring Emissions in GtCO₂

• GtCO₂: Gigatonne of CO₂ (per year):

  • equivalent, 1,000,000,000 metric tonnes.

  • We will work with ≈ 1–50 GtCO₂.

• Be careful: 1 GtC (carbon) is not 1 GtCO₂:

  • The difference is oxygen.

  • 1 tC = 3.5 tCO₂ .

  • Social Cost of Carbon is badly misnamed. The quoted $-figures are really the Social Cost of Carbon-Dioxide (CO₂).

• we hope carbon sinks won’t exhaust.

  • e.g., warmer oceans may bubble out more CO₂

• 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):

• CO₂ (3/4 of GHG, longest-term).

• Methane CH₄ (1/8 of GHG).

  • Much more opaque to IR

  • immediate control has big short-term payoffs.

  • CH₄ decays to ≈ minute CO₂.

• Other (NOx, CFC).

Global Warming Potential (GWP)

• CH₄ warms more, but doesn’t last as long.

• CO₂: GWP=1.

• GtCO₂e: 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 CO₂.

• 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.

• ≈ 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 GtCO₂ Fuel Emissions (Only CO₂)

Methane And NOx: GtCO₂

Circle Plot

GHG Sources

Electrifying

• Think 25-35 GtCO₂e is easily electrifiable.

• Think 15-25 GtCO₂e is not (ag, flying, etc.)

Summary

• World GHG emissions are huge,

• and still accelerating,

  • although rate of acceleration (3rd derivative) is slowing.