The cowl induction is taking advantage of the high pressure area at the base of the windshield when the vehicle is moving. It's to let cool air into the carburetor. Not to let hot air out of the engine compartment.
http://www.chevelles.com/feature/november_engine.jpg
see how the hood seals to the open area of the air cleaner?
The other intake for the air cleaner on the right is sealed off by a thermo-reactive spring when the engine reaches operating temperature.
It's not to let heat out.
On a Civic? Lifting the back of the hood is pointless. Almost every Honda I've ever seen has the air filter at the other end of the engine compartment. The best it can do is nothing. The worst is that it screws up your aerodynamics.
The area at the base of the windshield is under pressure. Roll up the windows in your Civic, switch the A/C fan completely off, switch from RECIRC to outside air, and drive 60 mph. You'll feel air coming through the dash vents. That air is hitting the windshield and being diverted back under the hood and into the cowl. That's why there is a rubber seal between the engine compartment and the cowl.
If you do this mod and you have any exhaust leaks under hood, you'll probably asphixiate in bumper to bumper traffic.