# What proportion of a flight do planes spend in the upper atmosphere?

While creating a methodology for the carbon footprint of flights, I came across some information which required the calculation of the distance travelled by a flight in the upper atmosphere. Essentially, aircraft emissions at higher altitudes have a larger climate impact than ones at lower altitudes and to compensate for that, we multiply the emissions when the aircraft is in the upper atmosphere by a constant like 5.2.

It is recommended to apply the factor if possible only on the emissions in the higher atmosphere because this allows for a better differentiation between short and long-distance flights

I have almost no knowledge about aviation and so it was hard for me to gather any information for how I could go about calculating the distance travelled in the upper atmosphere (and then calculate emissions based on the fuel consumption for that distance). I came across a diagram that showed the stages of flight and I guessed that I was attempting to find the proportion of the flight in cruise mode.

After going through this question on the aviation stack exchange, I figured a good estimate for the distance spent in the en route stage is the total distance travelled minus 60 NM, but I'm not sure if looking at the en route stage is what I want.

Could someone help me understand a way I could calculate the proportion of a flight that that the aircraft travels in the upper atmosphere? So far I'm expecting to multiply the total distance travelled by a given proportion, say 70%, given that the flight is long enough. Even if such a simple proportion isn't available, is there a way I could potentially calculate it given the origin and destination of a flight (and access to no financial resources for paid databases)?

Note: I was unaware that the 'upper atmosphere' had no standard meaning, so for this question defining it as above the troposphere is probably what I want as suggested by @Ben. This also restricts the question to commercial jets as pointed out by @jamesqf

• I think I have to ask the obvious question, if you have almost no knowledge of aviation, are you the best person to be creating this methodology? There are many secondary questions such as what do you mean by upper atmosphere, what pollutants are you interested in studying and so on.
– Frog
Jun 17, 2021 at 22:35
• How do you want to define "upper atmosphere"? Because aircraft tend to cruise near the boundary of the troposphere and the stratosphere, which are the two lowest levels of the atmosphere. No aircraft reaches the ionosphere/mesosphere which I would consider to be the upper atmosphere (but I'm sure some boffins have made their own definition for what counts as upper to suit their study goals)
– Ben
Jun 17, 2021 at 22:55
• A jet airliner cruising at something like 35,000’ does NOT start descending at 30nm. An old rule of thumb is 3 times your altitude, so 35,000’ x 3 = 105nm (3 nautical miles per 1000 feet ) Jun 18, 2021 at 0:15
• @Ben: "aircraft tend to cruise near the boundary of the troposphere and the stratosphere"? That's roughly 25K-50K feet (9-17 km). Most of us probably don't often get above 14K ft or so (and the only times I've been higher have been in sailplanes). Question needs to be limited to commercial jets & military aircraft. Jun 18, 2021 at 4:56
• The question is clear: do we on the Aviation site know what is defined as the Upper Atmosphere, referenced in an article on pollution. Voted to keep open. Jun 20, 2021 at 8:57