80% would be electrifying all road transport and making grid electricity renewable, and converting processes to electricity (primarily converting home heating). Road+heating+residential electricity is about 70% of co2 in the us and 50% of methane. The remainder is industrial use of electricity.

NB that this claim is in response to a proposed solution of building a gun to shoot a sun shield into space. The difficulty is relative. One is incredibly easy compared to the other.

Electricity isn't an energy source. Right now the US generates ~65% of electricity from burning coal and natural gas[1]. This is a common misconception with hydrogen fuel cells as well, which are chemical batteries, not energy sources.

While I agree with your general sentiment in this thread, simple electrification isn't enough; we also have to roll out major renewable energy generation and storage (which is still far wiser than building a gun to shoot a sun shield into space).

[1]: https://www.eia.gov/tools/faqs/faq.php?id=427&t=3

mistyped and left out 'renewable' grid electricity. In my defense, I have norovirus right now and my brain is currently flowing towards a water treatment facility somewhere.

Even converting all of those sectors to electric/renewable, you don't remove all greenhouse gases, you cut them down. In the case of personal transportation we see estimates of ~53% reduction in carbon footprint. I don't know what the improvements would look like if all utilities were forced to go renewables but we would certainly see large increases in price.

...and where would the electricity come from?

This doesn't seem easy at all.