"The grounding of planes for three days in the United States after September 11, 2001 provided a rare opportunity for scientists to study the affects of contrails on climate forcing. Measurements showed that without contrails, the local diurnal temperature range (difference of day and night temperatures) was about 1 degree Celsius higher than immediately before; however, it has also been suggested that this was due to unusually clear weather during the period." - Wikipedia

My teacher was talking about this in my lame Environmental Science class yesterday, and I told her that this was just variance and she continued rambling with no facts other then it just happens, does anyone have any knowledge into this that I can throw in her face tomorrow?

The irony of all this is daunting, but I'll refrain from the hijack.

please don't get Nielsio started on 9/11

small sample size. but i would imagine air travel does affect climate but on an almost negligible scale

As long as we have data from every other day for a decent amount of time, we can make some resonable estimates on the chances that this fluctuation was not caused by something 9/11 related.

i highly disagree

Ready.

So if the temperature change was 10 standard deviations from the mean measured over 100k days you would not think that something related to 9/11 may have caused this?

well it wasnt

You have data?

There was an episode of Nova about this a year or two ago. It was called "Dimming the Sun"

http://www.pbs.org/wgbh/nova/sun/

An article specifically about the contrail effect

http://www.pbs.org/wgbh/nova/sun/contrail.html

what if it's 2 standard deviations out? how do you calculate the probability it was 9/11 related?

just point out the math that is taking place here.

is the total amount of hot air produced by all jet engines over the US, compared with the total amount of airspace over the US, proportional to the temperature change? (did canada cancel all of their flights also?)

to do this, you are going to need a rough estimation of the total number of jet engines that are flying on a typical day. and an estimation of how many cubic feet of hot air each average engine is producing per second. you are also going to need an estimation of the ave temperature of the hot air produced.

then take this number and compare it to the total amount of airspace over the US. multiply this airspace by the ave daily temperature. and then multiply that by the total number of seconds in a day.

after you have these two numbers, find the ratio between them.

does this ratio correlate to the ratio of the temperature decrease that was experienced?

it is important to do this on the kelvin scale.

Nielsio has opinions about 9-11?

Most likely you will not be able to. But you calculate the odds that it was due to chance. Or more preciesly, given that 9/11 is just a normal day what is the chance that we see a temperature fluctuation as high as on 9/11.

Huh? Why is this important? I am not sure what your analysis will tell us. We know that was less air released after 9/11 and we know that the temperature difference was higher. No matter what the real cause was, we can express the temp change as some function of the lack of hot air. Since we only have one data point this will always be consistent.

on the small chance that you aren't leveling me, yes he does http://forumserver.twoplustwo.com/showthread.php?t=1331

no the theory is that the contrails reflect sunlight back into space so on 911 since planes grounded thus no congtrails, more sunlight got through on that day.

There is an unavoidable small-sample-size issue with September 2001. The results from those few days may or may not be significant.

But there ARE credible papers relating frequency of jet travel with increased cloudiness, both in the usual high-cloud zone and higher for noctilucent clouds. Here is one paper for you to chew on:

http://climate.gi.alaska.edu/Researc.../AKpaper4.html

With 9/11, the sample size is really to small to learn anything. However, it is very well documented that the pan evaporation rate (the rate of evaporation of water left outside) decreased as particulate polution increased. It is the same theory. More particles in the air means less light gets to earth's surface.

It is not just sample size issue, it is small sample size and a small effect relative to day to day unexplained fluctuations.

EDIT:
Actually I don't even know for sure that the effect is really small, but I think it most likely is.