Wikipedia:Reference desk/Archives/Science/2020 January 10

= January 10 =

Effects of aviation on climate change via contrails
Aviation is supposed to cause climate change not only due to CO2 emission, but also through other mechanisms, such as forming of contrails, cirrus clouds and ozone. However, these effects are short-lived. As far as I understand, when calculating the global future effect of a flight, say for 20 years from now, one takes the effect of, for example, the cotrails formed, multiplies by their duration, and then divides by 20 years.

This seems great if I want to either calculate the average effect over the next 20 years, or if I want to see the effect of trends in global aviation.

However, ignoring the differences between day and night, summer and winter etc., if I am interested in the effect of my next flight on the climate 20 years from now, this seems like a wrong calculation: Any transient effect lasting hours, days or even a year, will most probably fade away totally by the time 20 years have passed. Thus only the CO2 emission will actually have any effect 20 years from now.

Is this true? Thanks! Dan Gluck (talk) 17:12, 10 January 2020 (UTC)
 * Unless the effect isn't transient in the bulk; one flight may leave a transient amount of cloud formation which would dissipate if that were the only plane in the air. All flights together, taken as a group, are essentially permanently adding that effect to the atmosphere, because the effect never dissipates.  -- Jayron 32 17:41, 10 January 2020 (UTC)
 * Additionally, you are likely describing countering effects. Contrails and cloud formation increase the Earth's albedo, which has a local cooling effect. This could, on the short term, seemingly mask or reduce some of the warming effects of the CO2, but once the clouds and contrails dissipate, the albedo drops, and the warming effects are not masked. Your one flight will not have impact from controls and cloud formation directly during the flight in 20 years. Its carbon output might still be felt. However, even that is overly simplistic. If we stopped all industrial activity, all transportation activity, all agriculture, all aviation, etc., i.e. if we stopped all anthropogenic carbon emissions today, CO2 in 20 years might drop (possibly significantly). That is, unless we have already passed through a tipping point. It isn't the one flight or the one driving your car that's the issue in 20 years, it's the constant/increasing levels of carbon output that's the issue. To take one action and try to measure the 20 year impact ignores that the levels are a result of constant, and not transient output. --OuroborosCobra (talk) 18:22, 10 January 2020 (UTC)


 * Thanks for that, but you haven't really answered my question. Obviously one flight doesn't do much - it's the aggregation of flights that does. But one still may ask what is the contribution of one flight to that aggregate. The constant rather than transient effect you are referring to is due to the fact that there are flights all the time, but that is not what I've asked.
 * When refering to policy-making, there is not much of a difference. But When thinking about how personally I should change my behaviour in order to reduce my personal contribution to the climate change, it does matter. Dan Gluck (talk) 09:58, 11 January 2020 (UTC)
 * Unless you are changing your personal behavior to be flying 10 times per year every year for 20 years vs not flying, no, you aren't really doing much through your personal action alone. The climate impact in 20 years of a SINGLE airline flight is not something measurable as its impact doesn't last 20 years. The aggregation of flights occurring every day, constantly, is the effect. I'm sorry if that's not an answer that you like, but that is the answer. If you want to know what the impact of your next flight, and only that flight, is in 20 years, then the answer is "basically none." If you want to know your impact of changing your behavior to not fly on vacations every year for 20 years, then we can start talking about impact. --OuroborosCobra (talk) 22:22, 13 January 2020 (UTC)
 * To use a metaphor on this, lets say you want to know the impact in 20 years of you taking a cup of sand from a beach. The answer will be "essentially none." In those 20 years, that sand will have more than replenished through things like weathering and breakdown of rocks, deposition of material, etc. Now, let's change the question to be "what is the impact, in 20 years, of me taking a cup of sand from the beach every day for 20 years." Well, now you might be removing sand at a faster rate than replenishment, so you might, in 20 years, have a measurable impact. Let's change the question again. Now, "what is the impact in 20 years of 500 people each taking a cup of sand from the beach every day for the entire 20 years." Well, now the impact might very well be that the entire beach has no sand left by 10 years from now, and is never able to recover, or at least not until several decades (maybe centuries or more) after human activity has ceased, assuming it can at all. Do you see why asking "what is the impact in 20 years of my taking one cup of sand from a beach today" seems like a non-nonsensical question, one that is not even measurable? The damage threatening the beach in 20 years isn't one cup of sand today. It's 500 cups of sand, every day, constantly. Now, if we take away the "impact in 20 years" part from your question, the CO2 output and immediate impact of your airline flight is measurable. Asking about its impact in 20 years is the problem, because the effects are too transient for that. --OuroborosCobra (talk) 22:28, 13 January 2020 (UTC)
 * The 2007 IPCC summary cited in the article section has a positive (0.01 [0.003 to 0.03]) value for radiative forcing, but a "Low" assessed level of scientific understanding. Another source, from New Scientist states On average, both thin natural cirrus clouds and contrails have a net warming effect. The discussed study is here, maybe it or one of its references may help.&mdash;eric 17:26, 11 January 2020 (UTC)