Wednesday, 22 June 2005
The potential impacts of jet contrails on surface climate have been widely discussed in recent years with a growing body of evidence demonstrating a signal already exists in the current climate record. We demonstrate that contrail frequency in the conterminous United States has increased by more than an order of magnitude from the late 1970s to the recent contemporary period (2000-02). Although much of the contrail frequency increase (CFI) can be attributed to a similar increase in the amount of airplane flight miles, the spatially asymmetrical nature of the increase suggests that there are other controlling factors that need to be considered. We demonstrate a strong positive association between those regions experiencing the greatest (least) CFI and those experiencing the largest temperature decreases (increases) in the upper troposphere region nearest to typical cruising altitudes (the tropopause). We show that larger-scale teleconnections, potentially responding to global-scale climate change, may also be an important factor that can potentially be used to assist in predicting future changes in CFI.
As a means to reduce the current and future surface climate influence of contrails, and with projections of future increases in aviation dependency in mind, it is prudent to consider implementing policy that would reduce the potential for their formation. Previous studies have proposed the lowering of maximum cruising altitudes to reduce contrail frequency, an idea that is supported by the findings presented here. We propose adding a horizontal component to this effort by suggesting that aircraft avoid areas along flight routes that show a high likelihood of contrail formation and persistence based on meteorological analysis. To assess the feasibility of this suggestion, we demonstrate the typical spatial characteristics of contrail outbreaks, or clusters of contrails, that occurred during the 2000-02 mid-season months. We argue that the vast majority of contrails occurred within relatively small, mesoscale-sized regions of this type, and avoidance of such areas would substantially reduce contrail frequency without creating a major impact on travel time or fuel cost.
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