There are 10s/100s of pollutants. Hydrocarbons, VOCs, free radicals, dust, smog, microplastics, and more. Why are only CO2 emissions so universally used as a metric for climate targets? Surely measuring just the greenhouse effect isn’t sufficient as an indicator of overall climate health.

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There are 10s/100s of pollutants. Hydrocarbons, VOCs, free radicals, dust, smog, microplastics, and more. Why are only CO2 emissions so universally used as a metric for climate targets? Surely measuring just the greenhouse effect isn’t sufficient as an indicator of overall climate health.

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I think we need to put the greenhouse effect of CO2 into perspective, then:

CO2 is the universal measure, because we can measure it rather accurately, we are producing a whole lot more of it than we actually need to be, and it is, on its own, causing heavy meteoroligcal aberrations from rapidly heating planet.

The rest of these are significantly more “localized” effects, or are so much less bad than CO2 for the planet’s general health that it would take them a few decades to do to our health, what CO2 will do within 5 years.

Essentially, the answer is essentially “because it affects everyone”.

Microplastics and similar pollutants don’t have an effect on the climate. They’re dangerous for life on earth in different ways, but dumping a bunch of plastic into the sea won’t cause climate change.

Dust and smog affect only a localized area, they’re not constant and not global.

CO2 is used as the base because it’s by far the most plentiful greenhouse gas and because a lot of other pollutants eventually decompose into it.

CO2 is the current globally scary one that’ll likely impact all our lives.

Air pollution (VOCs, etc) is a big issue in cities and is also targeted by new rules in many places. For instance car/emissions free zones in many European cities, driving limitations in China, even straight up removal of arterial roads in some areas, etc.

Ozone depleting chemicals used to be huuge concern as well, but we’ve actually mostly curved the issue and the ozone layer is recovering. I’ve read near future sci fi written back then that assumed we’d need UN handouts of suncream, sunglasses and hats to avoid cancer.

The first point is the massive scale of our CO2 output. Humans have released 1.1 trillion tonnes and we’re adding 35 billion tonnes per year. What other chemical is anywhere near that level?

Secondly, we don’t only concentrate on CO2 but instead, use the term “CO2-equivalent” which includes the contribution of other greenhouse gasses. A big one is methane which is released with fossil fuel extraction (it’s a fossil fuel itself), in agriculture (e.g., cow farts), and rotting vegetation. Methane has a CO2-equivalent score around 30 (over 100 years) so our emissions of 360 million tonnes per year adds 11 billion tonnes to our CO2-equivalent emissions.

1) Most of those other species aren’t actually bad for the climate from a GHG perspective, they’re just bad for living things in the vicinity of where they’re being emitted.

2) CO2 is the lion’s share of both the emissions and the influence on Greenhouse Warming, even if it’s a relatively weak GHG.

3) From a combustion and power production standpoint, not only are you basically guaranteed to produce CO2, but you actually *want* to produce CO2…and nothing else. Essentially any other emission (other than water vapor) is unused energy, and thus lost efficiency (which, from a consumer standpoint, is wasted money). Hence, as regulators chase efficiency standards, it becomes easiest to relate all other GHGs to their equivalent mass of the GHG that you want to be producing (as opposed to other GHG species).

4) The goal has never been to form an indicator of “overall climate health,” only GHG potential. There is no single metric of “overall climate health,” other than (in a roundabout way) population figures from at-risk species.