Is there a trend in cirrus cloud cover due to aircraft traffic?

Abstract

Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in cirrus. Still we regard the results to be indicative of an impact of aircraft on cirrus amount. The main emphasis of our study is on the area covered by the ME-TEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic contrasts with a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm −2 (lower limit 0.01, upper limit 0.08 Wm −2) for the radiative forcing due to aircraft induced cirrus. The mean is close to the value given by IPCC (1999) as an upper limit.

A study on natural and manmade global interannual fluctuations of cirrus cloud cover for the period 1984–2004

“…Apart from their natural formation, cirrus cloud formation over the high air traffic northern mid-latitudes is also related to anthropogenic sources such as aviation activities (Zerefos et al, 2003;Minnis et al, 2004;Stordal et al, 2005;Stubenrauch and Schumann, 2005). Air traffic may contribute to high-level cloudiness by producing contrails (direct effect), which can then be transformed into contrail-cirrus clouds, or indirectly, by emitting soot and other particles which can stay in the atmosphere and get involved in cloud formation processes (Lohmann and Feichter, 2005;Sausen et al, 2005;Schumann, 2005).…”

“…In the ISCCP D2 satellite cloud dataset, cirrus clouds are defined as those with optical thickness less than 3.6 and cloud top pressure less than 440 mb. High cloud amounts from this data set have been compared with those from SAGE II (Liao et al, 1995) and have been recently used in several contrailcirrus-climate studies (Zerefos et al, 2003;Minnis et al, 2004;Stordal et al, 2005). In order to avoid artificial satellite cloud retrievals after the Mt.…”

“…Therefore, in northern mid-latitudes the percent of the interannual variance of CCC explained by NAO does not exceed the amplitude of the annual cycle. Furthermore, to evaluate the significance of the anthropogenic (aviation) effect with respect to the natural variability we have compared our results with manmade longterm trends over Europe and the NAFC as evidenced from earlier studies (Zerefos et al, 2003;Stordal et al, 2005;Stubenrauch and Schumann, 2005). According to Sausen et al (1998), at altitude levels around 300 hPa regions that are susceptible to the formation of contrails are located more in the extra-tropics than over the tropics.…”

“…The results are also compared with observed long-term trends in CCC over congested air traffic regions in Europe and the North Atlantic (Zerefos et al, 2003;Stordal et al, 2005;Stubenrauch and Schumann, 2005) to evaluate the significance of the anthropogenic (aviation) effect with respect to the natural variability. To account for dynamical and thermo-dynamical influences on CCC variability, cirrus cloud averages have been studied in relation to large-scale meteorological parameters such as vertical velocities and relative humidity.…”

Reframing the climate change challenge in light of post-2000 emission trends

“…Similarly, there remain significant uncertainties as to the radiative forcing impact of non-CO 2 emissions from aviation, particularly contrails and linear cirrus (e.g. Stordal et al 2004;Mannstein & Schumann 2005). …”