# Was the US brighter / warmer after the September 11th attacks grounded air traffic? **URL:** \ **Category:** Factual Questions\ **Created:** [June 2, 2006, 5:42pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169 "2006-06-02T17:42:58Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Lama\_Pacos](https://avatars.discourse-cdn.com/v4/letter/l/d6d6ee/32.png) [@Lama\_Pacos](https://boards.straightdope.com/u/Lama_Pacos)\ **Post date:** [June 2, 2006, 5:42pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/1 "2006-06-02T17:42:58Z")
I just read that for the three days after September 11th attacks, because air traffic was grounded, the US was unusually sunny, and with brighter nights, and that the overal temperature during that period was also one degree celsius higher than normal. Is this at all true? Does anyone have a cite for this? ---
**Author:** ![UncleBeer](https://avatars.discourse-cdn.com/v4/letter/u/977dab/32.png) [@UncleBeer](https://boards.straightdope.com/u/UncleBeer)\ **Post date:** [June 2, 2006, 5:56pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/2 "2006-06-02T17:56:13Z")
The U.S. is a pretty big place - especially when you consider that some portions of it are separated by vast distances from the contiguous 48 states. Kinda hard to draw a general conclusion of any kind. Even more absurd, it’s a long, _long_ way from determining that a short, small rise in the “overall temperature” (assuming _that_ term can even be defined in a way that allows us to conclusively quantify it - which I strongly doubt) actually occured to being able to directly attribute the rise to the grounding of air traffic. So, you tell me. What _is_ the “overall normal temperature of the United States” in early-to-mid September? It sounds to me like you’re actually looking for a “normal” percentage of cloud cover, rather than a temperature. And trying to conclude that if there were fewer clouds, it must have been due to the lack of air traffic. Problem with this is, clouds move; they don’t seem to respect international boundaries all that well. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [June 2, 2006, 6:10pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/3 "2006-06-02T18:10:41Z")
It’s not like the climate would respond instantly to a localized grounding of airplane. The world is a very big system, and takes years or decades to respond to global influences. So, what the OP read was false. ---
**Author:** ![happywaffle](https://avatars.discourse-cdn.com/v4/letter/h/ee59a6/32.png) [@happywaffle](https://boards.straightdope.com/u/happywaffle)\ **Post date:** [June 2, 2006, 6:11pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/4 "2006-06-02T18:11:24Z")
Actually, I read a thing back in '02 about a couple of meterologists who actually studied and did notice SOME change in weather from the lack of airplane contrails in the sky. Been too long, though, don’t have a URL or any data. I would doubt that it made a huge difference. Certainly nothing that your average Joe on the street noticed. ---
**Author:** ![Blaster\_Master](https://avatars.discourse-cdn.com/v4/letter/b/cab0a1/32.png) [@Blaster\_Master](https://boards.straightdope.com/u/Blaster_Master)\ **Post date:** [June 2, 2006, 6:15pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/5 "2006-06-02T18:15:02Z")
> [@Lama Pacos](#): > > I just read that for the three days after September 11th attacks, because air traffic was grounded, the US was unusually sunny, and with brighter nights, and that the overal temperature during that period was also one degree celsius higher than normal. Is this at all true? Does anyone have a cite for this? This sounds totally bunk to me, or at the very least impossible to support. Even if all these things are true (sunnier, warmer, brighter nights), its hard to attribute a three day spike to anything more than a slight anomaly. Maybe if air traffic were stopped for weeks, or months, you might be able to draw a more concise corelation. Add to what **UncleBeer** said, what exactly does “normal” mean? Taking an average over the lower 48 for those three days is pretty much a useless value because of the vast climate differences. Can you provide a link to the source where you read this? Do they provide a source for their numbers and how they derive these statistics? Do they provide any potential explanations as to how reduced plane travel (I’m quite sure the military was still flying) could cause this much of an effect? ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [June 2, 2006, 6:18pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/6 "2006-06-02T18:18:53Z")
> [@Lama Pacos](#): > > I just read that for the three days after September 11th attacks, because air traffic was grounded, the US was unusually sunny, and with brighter nights, and that the overal temperature during that period was also one degree celsius higher than normal. Is this at all true? Does anyone have a cite for this? I think it was from all those people burning candles for the satellite photo. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [June 2, 2006, 6:24pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/7 "2006-06-02T18:24:18Z")
I think the effect of contrails can’t be overlooked as they will reflect light back into space. Near airports with the right conditions you can sometimes see long thin clouds that are all in line from the planes. Now I don’t see it effecting rain patterns, but over flight paths it would seem like the ground will get more sunlight. ---
**Author:** ![Lsura](https://avatars.discourse-cdn.com/v4/letter/l/7993a0/32.png) [@Lsura](https://boards.straightdope.com/u/Lsura)\ **Post date:** [June 2, 2006, 6:35pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/8 "2006-06-02T18:35:08Z")
I don’t know if it affected temperatures during the days after, but there was a study done during that time (I haven’t read the actual story and only remembered this because I read a story about it in the NY Times at one point that was fascinating). [CNN story](http://archives.cnn.com/2002/TECH/science/08/07/contrails.climate/index.html) [ScienceNews](http://www.sciencenews.org/articles/20020511/fob1.asp) [html version of the study that spawned the articles](http://72.14.207.104/search?q=cache:t7OQy6uOgMUJ:academics.uww.edu/geography/Proceedings%2520Paper.doc+contrails+%22september+11%22&hl=en&gl=us&ct=clnk&cd=1). Also available in [doc format](http://academics.uww.edu/geography/Proceedings%20Paper.doc) ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [June 2, 2006, 7:02pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/9 "2006-06-02T19:02:47Z")
> [@silenus](#): > > So, what the OP read was false. Or it not false (insofar as such impossibly broad metrics can be supported), then coincidental. ---
**Author:** ![Marley23](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Marley23](https://boards.straightdope.com/u/Marley23)\ **Post date:** [June 2, 2006, 7:19pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/10 "2006-06-02T19:19:20Z")
September 11th itself was said to be an unusually clear day throughout the continental United States. So I’m not sure how someone could say “the next three days were sunny, and it must be because the planes were grounded.” The weather was already like that. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [June 2, 2006, 7:53pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/11 "2006-06-02T19:53:26Z")
Please actually read the links posted in post #8 before adding personal opinion that the climate effect wasn’t real. Particularly parts like this: > [@](#): > > Travis’ results are difficult to argue with, says Patrick Minnis of NASA’s Langley Research Center in Hampton, Va. This was apparently a measurable effect. Sailboat ---
**Author:** ![Baraqiyal](https://avatars.discourse-cdn.com/v4/letter/b/ecccb3/32.png) [@Baraqiyal](https://boards.straightdope.com/u/Baraqiyal)\ **Post date:** [June 2, 2006, 8:02pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/12 "2006-06-02T20:02:48Z")
PBS’s [Nova](http://www.pbs.org/wgbh/nova/sun/contrail.html) covered this a few weeks ago. According to their report, aircraft contrails contribute slightly to global dimming (which slightly offsets global warming). When the aircraft were grounded on September 11, the temperature did indeed go up due to the absence of contrails (according to the climate experts they talked to). ---
**Author:** ![Marley23](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Marley23](https://boards.straightdope.com/u/Marley23)\ **Post date:** [June 2, 2006, 8:04pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/13 "2006-06-02T20:04:28Z")
> [@Sailboat](#): > > Please actually read the links posted in post #8 before adding personal opinion that the climate effect wasn’t real. The article, which is very interesting, doesn’t directly address the “sunny” comment in the OP. ---
**Author:** ![threemae](https://avatars.discourse-cdn.com/v4/letter/t/5f9b8f/32.png) [@threemae](https://boards.straightdope.com/u/threemae)\ **Post date:** [June 2, 2006, 8:14pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/14 "2006-06-02T20:14:57Z")
Apparently these jokers made it into _Nature_ so I might advise some of the more incredulous posters to hold their tongues until they read the article. It isn’t an enormous effect but it seems significant. ": The magnitude of the 2001 increase (1.8 C) is the only value for all 31 years that is 2 standard deviations away from the mean value in either a positive or negative direction (SD=0.9 C). This suggests that factors other than air mass changes may have contributed to the large DTR increase seen during Sept. 11-13, 2001. It is worth noting that this analysis is for the entire continental U.S., with no additional weight given to those stations located in areas where contrails are most frequent. Hence, the DTR differences between 2001 and climatology shown here potentially underestimate the magnitude of the DTR change for those “favored” regions (e.g. U.S. Midwest). " "In contrast to the spatial variations shown in the 30-year mean map, the map for the Sept. 11-13, 2001 period shows that the largest DTR values spread eastward across portions of the central and northeast U.S. (Figure 5). When the two maps are compared, larger than “normal” DTR values are apparent for the Midwest, Northeast, and Northwest regions of the U.S. (Figure 6). We argue that at least a portion of this increase can be attributed to the lack of contrail coverage during the Sept. 11-13, 2001 aircraft grounding period. " Figures 6 and 7 from the .doc pretty much say it all. I’m 98% convinced. ---
**Author:** ![UncleBeer](https://avatars.discourse-cdn.com/v4/letter/u/977dab/32.png) [@UncleBeer](https://boards.straightdope.com/u/UncleBeer)\ **Post date:** [June 2, 2006, 9:17pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/15 "2006-06-02T21:17:31Z")
> [@Sailboat](#): > > Please actually read the links posted in post #8 before adding personal opinion that the climate effect wasn’t real. And yet measureable, does not give us cause and effect. Neither do the measurements reported in those links say it was “warmer.” They merely show that the difference between the high and low temps were wider than on either the three days previous, or the three days after. I will admit, however, that I’m more than a little astounded to find even this little bit of support for the claims in the OP. ---
**Author:** ![threemae](https://avatars.discourse-cdn.com/v4/letter/t/5f9b8f/32.png) [@threemae](https://boards.straightdope.com/u/threemae)\ **Post date:** [June 2, 2006, 9:31pm UTC](https://boards.straightdope.com/t/was-the-us-brighter-warmer-after-the-september-11th-attacks-grounded-air-traffic/359169/16 "2006-06-02T21:31:08Z")
> [@UncleBeer](#): > > They merely show that the difference between the high and low temps were wider than on either the three days previous, or the three days after. They involve quite a large collection of data beyond just the three days prior and after, in fact they compare this measurement to 31 years of prior data. Again, I refer you to figures six and seven in the .doc and tell me you don’t find their case rather convincing. Also, they provide a significant amount of background with a number of plausible explanations and factors contributing to their explanation. I think it’s pretty solid research.