Ik dacht dat cirruswolken een netto opwarmend effect hadden (positieve forcering op TOA) en contrails zou je daar ook onder kunnen rekenen. Of hebben zien ze witter vanwege de aërosolen die met de uitlaatgassen in de contrails oplossen?
Je hebt gelijk, het IPCC houdt het op een best-guess van +0,01 W/m² tussen 1750 en 2005 (zie figuur 2, hoofdstuk 2, pagina 136). In paragraaf 2.6 ('Contrails and Aircraft-Induced Cloudiness') staat verder dit:
The IPCC separately evaluated the RF from subsonic and supersonic aircraft operations in the Special Report on Aviation and the Global Atmosphere (IPCC, 1999), hereinafter designated as IPCC-1999. Like many other sectors, subsonic aircraft operations around the globe contribute directly and indirectly to the RF of climate change. This section only assesses the aspects that are unique to the aviation sector, namely the formation of persistent condensation trails (contrails), their impact on cirrus cloudiness, and the effects of aviation aerosols.
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Aircraft produce persistent contrails in the upper troposphere in ice-supersaturated air masses (IPCC, 1999). Contrails are thin cirrus clouds, which reflect solar radiation and trap outgoing longwave radiation. The latter effect is expected to dominate for thin cirrus (Hartmann et al., 1992; Meerkötter et al., 1999), thereby resulting in a net positive RF value for contrails.
Over Radiative Forcing Estimates for Aviation-Induced Cloudiness:
Regional cirrus trends were used as a basis to compute a global mean RF value for AIC in 2000 of +0.030 W m–2 with a range of +0.01 to +0.08 W m–2 (Stordal et al., 2005). This value is not considered a best estimate because of the uncertainty in the optical properties of AIC and in the assumptions used to derive AIC cover. However, this value is in good agreement with the upper limit estimate for AIC RF in 1992 of +0.026 W m–2 derived from surface and satellite cloudiness observations (Minnis et al., 2004). A value of +0.03 W m–2 is close to the upper-limit estimate of +0.04 W m–2 derived for non-contrail cloudiness in IPCC-1999. Without an AIC best estimate, the best estimate of the total RF value for aviation-induced cloudiness (Section 2.9.2, Table 2.12 and Figure 2.20) includes only that due to persistent linear contrails. Radiative forcing estimates for AIC made using cirrus trend data necessarily cannot distinguish between the components of aviation cloudiness, namely persistent linear contrails, spreading contrails and other aviation aerosol effects.
Ik heb mijn bericht aangepast.
Gr. Ben
