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@ARTICLE{Wilhelm:903168,
      author       = {Wilhelm, Lena and Gierens, Klaus and Rohs, Susanne},
      title        = {{W}eather {V}ariability {I}nduced {U}ncertainty of
                      {C}ontrail {R}adiative {F}orcing},
      journal      = {Aerospace},
      volume       = {8},
      number       = {11},
      issn         = {2226-4310},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2021-04888},
      pages        = {332 -},
      year         = {2021},
      abstract     = {Persistent contrails and contrail cirrus are estimated to
                      have a larger impact on climate than all CO2 emissions from
                      global aviation since the introduction of jet engines.
                      However, the measure for this impact, the effective
                      radiative forcing (ERF) or radiative forcing (RF), suffers
                      from uncertainties that are much larger than those for CO2.
                      Despite ongoing research, the so called level of scientific
                      understanding has not improved since the 1999 IPCC Special
                      Report on Aviation and the Global Atmosphere. In this paper,
                      the role of weather variability as a major component of the
                      uncertainty range of contrail cirrus RF is examined. Using
                      10 years of MOZAIC flights and ERA-5 reanalysis data, we
                      show that natural weather variability causes large
                      variations in the instantaneous radiative forcing (iRF) of
                      persistent contrails, which is a major source for
                      uncertainty. Most contrails (about $80\%)$ have a small
                      positive iRF of up to 20 W m−2. IRF exceeds 20 W m−2 in
                      about $10\%$ of all cases but these have a disproportionally
                      large climate impact, the remaining $10\%$ have a negative
                      iRF. The distribution of iRF values is heavily skewed
                      towards large positive values that show an exponential
                      decay. Monte Carlo experiments reveal the difficulty of
                      determining a precise long-term mean from measurement or
                      campaign data alone. Depending on the chosen sample size,
                      calculated means scatter considerably, which is caused
                      exclusively by weather variability. Considering that many
                      additional natural sources of variation have been
                      deliberately neglected in the present examination, the
                      results suggest that there is a fundamental limit to the
                      precision with which the RF and ERF of contrail cirrus can
                      be determined. In our opinion, this does not imply a low
                      level of scientific understanding; rather the scientific
                      understanding of contrails and contrail cirrus has grown
                      considerably over recent decades. Only the determination of
                      global and annual mean RF and ERF values is still difficult
                      and will probably be so for the coming decades, if not
                      forever. The little precise knowledge of the RF and ERF
                      values is, therefore, no argument to postpone actions to
                      mitigate contrail’s warming impact},
      cin          = {IEK-8},
      ddc          = {530},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {2111 - Air Quality (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2111},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000723773700001},
      doi          = {10.3390/aerospace8110332},
      url          = {https://juser.fz-juelich.de/record/903168},
}