Severe cooling? Don't make me laugh. An impact with that much energy on a Round Earth would superheat the planet for millennia. It would get trapped in the atmosphere. Look at Venus, for example. A Flat Earth, however, would allow the heat to escape much more quickly, out the sides.
Indeed, please let me see your calculations for this idea. Also cooling is heavily related to
surface area so heat dissipating from the entire surface of the globe would be radiated much more quickly than that of a small ring from the edge of a disc. It would of course also radiate from the top surface of the disk and bottom.
Here is some info about the impact.
Estimated Chicxulub Parameters:
Projectile diameter: 12.00 km ( = 7.45 miles )
Projectile Density: 3000 kg/m^3
Impact Velocity: 20.00 km per second ( = 12.40 miles per second )
Impact Angle: 90 degrees
Target Density: 2700 kg/m^3
Target Type: Liquid water of depth 500.0 meters ( = 1640.0 feet ), over crystalline rock.
Energy: Energy before atmospheric entry: 5.43 x 10^23 Joules = 1.30 x 10^8 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.0 x 108years
Major Global Changes: The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
(from
http://impact.ese.ic.ac.uk/ImpactEffects/Chicxulub.html)
That is a lot of energy. But super heating? Lets see what effect it would have had on ocean temperature. We will assume the energy was quickly evenly distributed across the entire ocean mass. Just to give us a quick back of the envelope idea.
A calorie is the energy needed to raise 1 gram of water 1 Kelvin or degree Celsius at 1 atmosphere.
1 calorie = 4.2 Joule so calories were 5.43 x 10^23 joules/4.2 = 1.293 x 10^23 calories
Total ocean mass of Earths oceans is 1.4 x 10^21 kg = 1.4 x 10^24 grams
So calories/mass = temp change
1.293 x 10^23 calories / 1.4 x 10^24 grams = 0.0924 degree temperature change.
Not even a degree! What was the main problem was all of the material thrown up into the atmosphere, and of course the devastation near the impact. In 1816 there was essentially no summer as a result of the 1815 eruption of Mount Tambora. This event had substantially less energy and was still able to wreak havoc. (
http://en.wikipedia.org/wiki/1815_eruption_of_Mount_Tambora)
There is still a great deal of debate as to whether this event was the cause, was a co-cause, or just a coincident of the extinction. But the evidence for it having occurred is substantial.