Ya good point — our approach is always spend-based, so the way we'd calculate cloud spend is your AWS / GCP bill * the AWS / Google carbon intensity (what we call a 'factor'). It is true that some data center regions use cleaner energy vs. others. We consider the spend-based approach, at a minimum, a good first pass. The greener the cloud you use, the lower the emissions. And then you can further optimize within your cloud provider.
Another note — most cloud emissions only factor in the energy footprint ('scope 2' in technical greenhouse gas inventory terms). We believe this significantly undercounts emissions, because it ignores the capital expenditure of building the facility, buying all the machines, etc. The great thing about the spend-based approach is all this overhead is factored in. (BTW, Google Cloud Platform just started to layer in some of this 'scope 3' operational overhead data, but I believe AWS still ignores it, significantly undercounting emissions).
Another note — most cloud emissions only factor in the energy footprint ('scope 2' in technical greenhouse gas inventory terms). We believe this significantly undercounts emissions, because it ignores the capital expenditure of building the facility, buying all the machines, etc. The great thing about the spend-based approach is all this overhead is factored in. (BTW, Google Cloud Platform just started to layer in some of this 'scope 3' operational overhead data, but I believe AWS still ignores it, significantly undercounting emissions).