Pledging Zero Carbon Emissions by 2030 or 2050: Does it Matter?

We now have two responses to the climate emergency battling it out among House Democrats, the “aggressive” 2030 target for net zero emissions folded into the Green New Deal and a more “moderate” 2050 target for the same, just announced by a group of mainstream legislators.  How significant is this difference?  Does where you stand on climate policy depend on whether your policy has a 2030 or 2050 checkpoint?

I say no.  Neither target has any more than symbolic value, and what the government does or doesn’t do to prevent a klimapocalypse (can we use this interlingual word?) won’t depend on which one gets chosen.

Endpoint targets have no constraining power at all.  A 2030 target won’t be met or unmet until 2030, and by then it will be too late.  Same, and worse, for a 2050 target.  Moreover, the whole target idea is based on a misconception of how carbon emissions work.  The CO2 we pump into the atmosphere will remain for several human generations; it accumulates, and the sum of the carbon we emit this year plus next plus the one after and so on is what will determine how much climate change we and our descendants will have to endure.  (The relationship between our emissions and the earth system’s response is complex and may embody tipping points due to feedback effects.)  Every additional ton of carbon counts the same, whether it occurs today or just before some arbitrary target date.

What we need instead is a carbon budget, an announced total quantity of emissions we intend to hold ourselves to, starting right now and continuing through the end of the century.  That way, whether we’re living up to our pledge or scrapping it is put to us each year based on how quickly we’re using up our quota.  It sets the meter running now.

As a secondary point, caveat emptor about the “net” emissions thing.  Net of what?  Purchased offsets like in California?  (My emissions don’t count because I’ve given you money so you won’t increase yours by as much as you said you might, and I’m hoping no one else will step up and do your emissions instead.)  Or investments in forests, that may or may not continue to store carbon in the decades ahead, and which may or may not cause more harvesting of other forests?  A proper carbon budget isn’t net of anything; it’s an amount of fossil carbon we set aside for ourselves to burn, and that’s it.  Anything else, like bulking up our forests or pursuing other forms of carbon sequestration, should be additional, because at this point no feasible budget alone can be tight enough.