First off, removing 2% of greenhouse gases isn't something to scoff at - it would be a really important accomplishment. Secondly, your back of the napkin math

First off, removing 2% of greenhouse gases isn't something to scoff at - it would be a really important accomplishment. Secondly, your back of the napkin math doesn't seem great - you're just making up that gases would be cut in half with nothing to back that up. You seem to ignore the fact that electricity for agriculture would disappear but then you factor in electricity that would be added back for food factories, so that doesn't make sense either. Then of course there's the fact that lab-grown meat doesn't require the vast swaths of land required by traditional agriculture. That means you can put food factories closer to urban centers, so now you've eliminated a lot of emissions from transportation.