It was nine years ago that the 9/11 terror attacks took place simultaneously in New York City and in Washington D.C. Immediately, the nation was gripped by a state of total shock. However, once the initial disbelief was over, climate scientists realized that, with all planes grounded, they had a golden opportunity to study the atmosphere as there were no planes to interfere.
Everyone has seen a jet contrail before, they’re the trail of exhaust that one sees trailing out behind a plane. Appearing thin right out of the plane, contrails can eventually dissipate to the degree that they resemble wispy cirrus clouds. Clouds impact the climate, so, the scientists asked, do contrails?
As it turned out, yes, the contrails appear to have power over climate. Naturally, the sun’s rays heat the atmosphere during the day. When there are no clouds to speak of, everything is clear-cut simple: sunlight warms the atmosphere and the air heats up. Sun goes down, the air cools, simple. However, throw clouds into the mix, and the story changes.
When it is cloudy during the day, the air doesn’t get as warm as it naturally would on a sunny day because many of the Sun’s rays are reflected back into space by the clouds. As a result, they don’t make it to the ground and the air remains cool. However, at night, the story is exactly the opposite. If it is sunny the majority of the day and then clouds come in late, the air is already heated. When the clouds come in, they act as a blanket, trapping the heated air on Earth and not allowing it to escape back intp space. That’s why cloudy nights are warmer than clear ones.
Back to the scientists.
Ideally, a scientific study of this magnitude (studying nationwide climate) would take place over years. Unfortunately, the planes would not be grounded forever, which left little time for measuring heating and cooling. However, during the course of the three day grounding, scientists determined that, compared to past weather records spanning many years, the days in September, 2001 when the planes were not flying averaged two degrees warmer during the day and two degrees cooler during the night.
The contrails are essentially acting as artificial clouds!
Shortly after the findings were concluded, the long-running PBS science series Nova ran a program on the findings, titled the Dimming the Sun. WVIZ PBS Cleveland has re-aired the program many times since then, so keep an eye on local listings to see for yourself the how the interaction between the nearest star and jet exhaust combine to impact our entire planet.
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