All space heaters operate at the same efficiency since they convert electricity to heat via resistance. You may have a small one and low electricity rates in your area to see a negligible change. Or maybe other uses went down and masked the increase from the space heater usage.

I can see how it’s strange on the surface, but ultimately the carbon emissions wouldn’t be there if the polluting activity was not funded. So to whom would the carbon emissions be attributed otherwise? Just the CEO?

The study’s primary metric appears to include both supplier and producer emissions proportional to income and investments. What alternative do you suggest?