What happens when $CO_2$ (and other gases) are emitted?

  • $CO_2$ isn't the only GHG (greenhouse gas). What about the others?
  • Earth's carbon cycle
  • Earth's water cycle
  • Comparing Global Warming Potential (GWP) of GHGs

$CO_2$ vs $H_2O$

Consider the chemical reaction for combustion of natural gas (methane):

The products are $CO_2$ and water.

Both are greenhouse gases (GHGs). Why don’t you hear anyone worrying about all the water from burning fossil fuels??

Carbon cycle

  • Project Drawdown gives cuts in emissions in Gigatonnes of $CO_2$(eq).
  • The diagram below is in terms of Petagrams.

    What's the relationship of these two units?

We figured out that 1 Pg = 1 Petagram = 1 Gigatonne.

  • Black number - Predating humans
  • Red numbers - human influence

Carbon flows (Pg / year)

$CO_2$ in Earth's atmosphere: Pre-industrial $CO_2$ levels, 280 ppm $\approx$ 589 Pg.

Human impact: +4 Pg / year

Human impacts that increase atmospheric $CO_2$

  • Burning fossil fuels: +7.8; 

  • Land use change: +1.1; 

  • Increased soil respiration + increased fire: +11.6


Some human impacts decrease atmospheric $CO_2$

  • Increase in $CO_2$ in the atmosphere, leads to Increased ocean absorption: -2.3; $\Rightarrow$ Ocean acidification… 

  • Increased photosynthesis / plant growth due to higher $CO_2$ levels: -14.1 Carbon is sequestered ("kidnapped" or "stored") in plants, until they are burned or broken down by bacteria. Four human ways to store plant carbon longer term?
    • Reduce de-forestation.
    • Expand forested land. ("Aforestation")
    • "Biochar" - make charcoal out of plants by heating them underground (without oxygen), and then bury the charcoal. This improves soil water retention, reducing runoff, and decreasing need for fertilizer. See also "Terra Preta"
    • Build with wood. Modern "Cross Laminated Timber" (CLT) can be used to construct multi-story buildings.

Ocean acidification

Lucky for our atmosphere, a large portion of the $CO_2$ we emit goes into the ocean!

...But when $CO_2$ dissolves in water it forms $H_2CO_2$-Carbonic acid, which

  • Contributes to coral "bleaching" (along with increased water temperatures and damage from boat anchors and bottom fishing...)
  • Weakens the calcium-carbonate skeletons / shells which many marine animals depend on.

    Water cycle

    • Water boils / condenses at +212 F

    Look up: How long does water stay in the atmosphere? What is the boiling temperature of carbon dioxide?

    How long does $CO_2$ hang around?

    Average temperatures will stop increasing when emissions stop, but cooling will take thousands of years as greenhouse gases slowly dissipate from the atmosphere.

    David Keith

    IPCC calculation

    IPCC = Intergovernmental Panel on Climate Change

    • Scientists / Diplomats / Business representatives
    • Convoked by the UN and the WMO
    • Studies CC and issues reports of their consensus.