One obvious problem with that is that horrible things can be justified with CO2 arguments, or tolerated because they have little obvious impact on CO2. This ersatz 'green' argument has been applied to tracking, nuclear power, big hydro, GMOs, and the conversation of forests into wood chips for biofuel. Now you might say these are specious arguments that depend on faulty carbon accounting (is nuclear power really that carbon friendly when you account for the immense amount of energy needed to mine the uranium, refine the uranium, procure the cement, contain the waste, etc.?) but I am afraid there is a deeper problem. It is that when we base policy on a global metric, i.e. by the numbers, then the numbers are always subject to manipulation by those with the power to do so. Data can be manipulated, factors can be ignored, and projections can be skewed toward optimistic best-case scenarios. This is an inherent problem with basing policy on a metric like tons of CO2 or GGEs (greenhouse gas equivalents).
Secondly, by focusing on a measurable quantity we devalue that which we cannot measure or choose not to measure. Such issues such as mining, biodiversity, toxic pollution, ecosystem disruption, etc. recede in urgency, because after all, unlike global levels of CO2 they do not pose an existential threat. Certainly one can make carbon-based arguments on all these issues, but to do so is to step onto dangerous ground. Imagine that you are trying to stop a strip mine by citing the fuel use of the equipment and the lost carbon sink of the forest that needs to be cleared, and the mining company says, "OK, we're going to do this in the most green way possible; we are going to fuel our bulldozers with biofuels, run our computers on solar power, and plant two trees for every tree we chop down." You get into a tangle of arithmetic, none of which touches the real reason you want to stop the mine -- because you love that mountaintop, that forest, those waters that would be poisoned.
I am certain we will not "save our planet" (or at least the ecological basis of civilization) by merely being more clever in our deployment of Earth's "resources". We will not escape this crisis so long as we see the planet and everything on it as instruments of our utility. The present climate change narrative veers too close to instrumental utilitarian logic -- that we should value the earth because of what will happen to us if we don't. Where did we develop the habit of making choices based on maximizing or minimizing a number? We got it from the money world. We are seeking to apply our numbers games to a new target, CO2 rather than dollars. I don't think that is a deep enough revolution. We need a revolution in means, not only a revolution in ends.