[vitus]

>> Let's brainstorm how to decarbonize fertilizer, or concrete.

> I don't think you can. I think you should worry more about how concrete and fertilizer get _distributed_. This is essentially the same dynamic as the home solar problem above.

Isn't the primary source of CO2 from fertilizer production a byproduct of producing hydrogen gas via steam methane reforming?

We can make hydrogen without starting from methane (namely: via electrolysis), but it's not economical in comparison, at this time. (Or clearly able to scale to quite the same degree, for that matter.) But I reject the claim that it's not possible (or, for that matter, that we don't know how to do it). The issue is that the negative externalities from CO2 emissions are not priced in such a way to render existing processes less cost-effective than carbon-free alternatives.

That said, I share some of your skepticism regarding how much we can conceivably decarbonize concrete production.