Add costs attributed to emissions (e.g. air pollution on human health) and CO2 (e.g. ocean acidification)

[hdrake]

Thanks to @phjacobs to reminding me to do this. He referenced https://www.nature.com/articles/s41467-019-09499-x as an example of how important this effect can be in economic evaluations of near-term climate policy.

[hdrake]

@lfreese, any other recommendations from the air pollution literature? What we're really after is a globally-averaged estimate of the cost (in $/yr) of CO2 emissions (or direct pollutants, which we can convert into equivalent CO2 emissions using some conversion factor).

[hdrake]

Just a note that this is actually a super easy thing to implement, all I really need is some kind of reference cost to tune the cost function to.

[hdrake]

In one figure of the MARGO paper, we add two diagnostic terms to the damage function:

• linear in CO2 concentration
• quadratic in warming rate

These are not active in the optimization and just used in a sensitivity analysis.