Empty Sky after 9/11 led to a warmer United States

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The attacks on September 11th took place 18 years ago. Two planes crashed into the World Trade Center the morning of September 11th. Planes were being used as guided missiles and no one knew how many planes were hijacked at that time. The Federal Aviation Administration or FAA was scrambling to gain control of the intense situation. The FAA ordered over 4,000 planes to land immediately after the attacks on the World Trade Center Towers. Within a couple of hours all planes beside military planes landed and were grounded until further notice. By the afternoon the sky was completely empty and remained empty for 3 days, until civilian aircraft were allowed to fly again.

Video Courtesy: Smithsonian National Air and Space Museum

So why did the United Sates warm after the attacks on 9/11?

According to the Nation Air Traffic Controllers Association there are over 87,000 flights that crisscross the United States everyday. Planes produce exhaust just like a cars and produce contrails (Condensation Trails). Contrails are created when water vapor from the engines freezes when exhausted into the sky. For every 1,000 ft in altitude you rise you roughly cool 4 degrees Fahrenheit. Commercial flights fly between 31,000 and 38,000 feet, about 5.9 to 7.2 miles above the earths surface. Between 30,000 and 40,000 feet the temperature ranges from -40 to -70 degrees Fahrenheit. The exhaust from the planes freeze instantly, producing a clouds. Clouds are formed when warm moisture air is forced up in the sky. As the moisture cools, it condenses into a cloud.

When over 87,000 flights fly over the United States a day, thousands of high cirrus clouds are being created. Clouds reflect sunlight back into space which would have otherwise reached the earths surface, warming us up. The opposite affect happens at night. The cloud cover traps the days heat to the surface and keeping us warm. On a clear sky night the maximum amount of radiative cooling would occur allowing our temperatures to fall.

The United States warmed about 3.6 degrees Fahrenheit after the attacks of 9/11. The fact that there were less planes in the sky and less clouds being made by the exhaust allowed for the maximum amount of heating to occur. Leading to the United States to temporarily warm up the 3 days after the September 11th attack.

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