Contrails and Cloudiness

Photo by Jim Angel, Champaign, IL, January 28, 2015.

This morning we had a brilliant display of airplane contrails, enough to significantly increase the cloudiness (as if we needed more cloudiness this winter). Despite rumors to the contrary, airplane contrails are just the byproducts of burning jet fuel at high altitudes where the air is very cold and dry. The basic chemistry involves combing a carbon-based fuel and oxygen to produce CO2 and water.  CH4 + 2O2 –> CO2 + 2H2O

It’s the same process you see on a cold morning with car exhaust. The water vapor exits the exhaust pipe and condenses when it hits the colder air temperature, resulting in a white fog.

There have been some studies (mentioned below) to suggest that airplane contrails can lead to regional increases in cloudiness over time. As a result, in certain regions the daytime highs may be lower and the nighttime lows higher. In other words, a reduction in the range of daily temperatures.

My predecessor Stan Changnon wrote about this in a 1981 study:

Records of monthly sky cover, sunshine and temperature for 1901–77 in a 10-state midwestern area were analyzed on a temporal and spatial basis to discern long-term trends and indications of shifts potentially due to added cirrus generated by jet aircraft since about 1960. The skycover data show generally long-term increasing frequencies of cloudy days and decreases in clear days since 1901. Percent of possible sunshine also shows a decrease but to a lesser extent than clear day frequencies. Changes have been greatest since the 1930’s. The greatest shifts to cloudier, less sunny conditions occurred since 1960 in an east-west zone across southern Iowa-northern Missouri, northern two-thirds of Illinois and Indiana, and extreme southern sections of Wisconsin and lower Michigan, the area where commercial jet traffic has been greatest. The long-term trends give evidence of natural climate changes, whereas the localized shifts to more cloudiness in the central area since 1960 suggest anomalous changes related to jet-induced cirrus. Months with moderated temperatures (below average maximum and above average minimum) have increased since 1960 in the central east-west zone and largely in summer and fall, the seasons with the major shifts to cloudiness.

Reference: Stanley A. Changnon, 1981: Midwestern Cloud, Sunshine and Temperature Trends since 1901: Possible Evidence of Jet Contrail Effects. J. Appl. Meteor., 20, 496–508. doi:<0496:MCSATT>2.0.CO;2

Another study by David Travis et al. looked at the 3 days after September 11, 2001, when all flights were banned.

The potential of condensation trails (contrails) from jet aircraft to affect regional-scale surface temperatures has been debated for years1, 2, 3, but was difficult to verify until an opportunity arose as a result of the three-day grounding of all commercial aircraft in the United States in the aftermath of the terrorist attacks on 11 September 2001. Here we show that there was an anomalous increase in the average diurnal temperature range (that is, the difference between the daytime maximum and night-time minimum temperatures) for the period 11–14 September 2001. Because persisting contrails can reduce the transfer of both incoming solar and outgoing infrared radiation4, 5 and so reduce the daily temperature range, we attribute at least a portion of this anomaly to the absence of contrails over this period.


Climatology: Contrails reduce daily temperature range. David J. Travis1, Andrew M. Carleton2 & Ryan G. Lauritsen1, Nature 418, 601 (8 August 2002) | doi:10.1038/418601a

By the way, contrails are not new. They have been around as long as planes have reached higher altitudes. In WW II pilots hated them because they drew attention to their aircraft. Here is a well-known photo with lower altitude B-17s with their higher flying P-47 escorts, all generating contrails.


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