People might choose to fly somewhere else instead though, so it doesn't necessarily reduce the overall amount of carbon emissions from air travel. Especially if you see Europeans deciding to go somewhere else in the Americas instead, which I've heard some of my friends considering. Although if Europeans choose to travel within Europe instead then yes we'd see a reduction as the distances are rather shorter (and with any luck some of them would go by rail)

On the point of air travel specifically, Canadians are being advised to use airports over land borders because if you are denied entry at U.S. customs at a Canadian airport, they cannot detain you as you are on Canadian soil.

So for Canadians still travelling to the U.S. it might actually increase their carbon footprint.

Or more, if Canadians travel to Europe instead of the US

until the airlines reduce flights, the planes still fly, just emptier

if you need to eat and decide not to go to your usual restaurant for whatever reason... do you stop eating altogether?