Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany.
Proc Natl Acad Sci U S A. 2010 Nov 9;107(45):19181-4. doi: 10.1073/pnas.1005555107. Epub 2010 Oct 25.
Estimates of the global radiative forcing by line-shaped contrails differ mainly due to the large uncertainty in contrail optical depth. Most contrails are optically thin so that their radiative forcing is roughly proportional to their optical depth and increases with contrail coverage. In recent assessments, the best estimate of mean contrail radiative forcing was significantly reduced, because global climate model simulations pointed at lower optical depth values than earlier studies. We revise these estimates by comparing the probability distribution of contrail optical depth diagnosed with a climate model with the distribution derived from a microphysical, cloud-scale model constrained by satellite observations over the United States. By assuming that the optical depth distribution from the cloud model is more realistic than that from the climate model, and by taking the difference between the observed and simulated optical depth over the United States as globally representative, we quantify uncertainties in the climate model's diagnostic contrail parameterization. Revising the climate model results accordingly increases the global mean radiative forcing estimate for line-shaped contrails by a factor of 3.3, from 3.5 mW/m(2) to 11.6 mW/m(2) for the year 1992. Furthermore, the satellite observations and the cloud model point at higher global mean optical depth of detectable contrails than often assumed in radiative transfer (off-line) studies. Therefore, we correct estimates of contrail radiative forcing from off-line studies as well. We suggest that the global net radiative forcing of line-shaped persistent contrails is in the range 8-20 mW/m(2) for the air traffic in the year 2000.
线性尾迹的全球辐射强迫估算主要由于尾迹光学厚度的巨大不确定性而有所不同。大多数尾迹是光学薄的，因此它们的辐射强迫大致与光学厚度成正比，并随尾迹覆盖率的增加而增加。在最近的评估中，平均尾迹辐射强迫的最佳估算值显著降低，因为全球气候模型模拟指出的光学厚度值低于早期研究。我们通过将气候模型诊断的尾迹光学厚度的概率分布与卫星观测约束的微物理云尺度模型得出的分布进行比较，从而修订了这些估算值。通过假设云模型的光学厚度分布比气候模型更现实，并且将美国观测到的和模拟的光学厚度之间的差异视为具有全球代表性，我们量化了气候模型诊断尾迹参数化的不确定性。相应地修订气候模型的结果将使 1992 年线性尾迹的全球平均辐射强迫估算值增加 3.3 倍，从 3.5 mW/m²增加到 11.6 mW/m²。此外，卫星观测和云模型表明，可检测尾迹的全球平均光学厚度高于辐射传输（离线）研究中通常假设的光学厚度。因此，我们还修正了离线研究中尾迹辐射强迫的估算值。我们建议，在 2000 年的航空交通中，线性持久尾迹的全球净辐射强迫在 8-20 mW/m²之间。
