Monday, June 20, 2011

Contrails, an ignored environmental problem

I think it is weird not many people consider contrails and the cloud it create, contrail cirrus, as very potential environmental problem. Some of the article bellow explain the problem.

A magazine from Volvo Aero about the environmental impact of fying, 2011
Air traffic does more damage as emissions are discharged at high altitude.

This is one of the fundamental climate problems for air traffic. When jet propulsion fuel is combusted at an altitude of 10,000 metres, the effect on the climate is greater than it would be if the fuel were combusted on the earth’s surface. The climatic effect of air traffc is due not simply to carbon emissions but also to other factors, such as emissions at high altitude of water vapour, nitrogen oxide and particulates.

Emissions trading in International civil aviation
At cruise altitude, apart from CO2 it is above all NOx, water vapour, contrails and cirrus clouds that contribute towards the greenhouse effect. Of these, only CO2 is included in the Kyoto Protocol. The radiative forcing of CO2 represents only a little more than one-third (37 %) of the total radiative effect of all climate-impacting avia-tion emissions (Lee/Sausen 2000).

As a result of aviation, emissions are expelled into the global atmosphere that contribute to climate change and the destruction of the ozone layer. Emissions and expelled particulates alter the concentration of greenhouse gases - carbon dioxide (CO2), ozone (O3) and methane (CH4). They also trigger off the formation of contrails and can encourage the occurrence of cirrus clouds. All of this contributes to climate change (IPCC 1999).

In a Special Report of the IPCC (1999), climatic impact was investigated and compared for three periods of observation (1992, 2015 and 2050). In the case of CO2, not only were aviation emissions at these points in time considered, but also the emissions that have accumulated since 1950. With contrails, on the other hand, only emissions from 1992, 2015 and 2050 were considered on account of their short retention time. It turned out that, for all periods of observation, the radiative forcing of contrails is greater that that of CO2. This can be attributed to the fact that the sensitivity effect of contrails is more intense than the accumulation and growth effects of CO2.

Aviation has been identified as contributor to anthropogenic changes in the Earth’s radiation budget. In particular this is due to the emission of greenhouse gases, soot, aerosols, and the formation of contrails and aviation induced cirrus clouds. Linear persistent contrails occur in an ice supersaturated atmosphere if the Schmidt Appelman criterion is satisfied (1). Cirrus clouds can evolve from spreading persistent contrails known as primary cirrus or contrail cirrus (2). Secondary cirrus occur due to locally increased soot and aerosol concentration, which might lead to the formation of cirrus clouds that would not form in the absence of air traffic (3; 4; 5).

Linear persistent contrails and aviation induced cirrus clouds were identified as main contributors to the overall aviation induced radiative forcing. It is estimated that linear persistent contrails contribute approximately 20% to the total aviation induced radiative forcing (7). This estimate considers a year 2000 scenario where cirrus clouds are excluded. Aviation induced cir rus clouds have the potential to cause a radiative forcing which exceeds the radiative forcing of all other emissions due to air traffic combined.

Rolls-Royce Aviation Power in the air
Carbon emissions have a direct and widely recognised effect on climate change. However, flying also creates other impacts. Along with CO2, aircraft engines produce emissions of water vapour and oxides of nitrogen. Water vapour in the engine exhaust under certain conditions can form contrails and these may evolve into cirrus clouds.

Glenn Research Center
Contrails contribute to the phenomenon known as "global change." Right now this effect is small, but it is growing. Although scientists are uncertain about the impact of contrails on global change, they believe that persistent contrails, those that last longer than a few minutes, gradually develop into cirrus clouds. Over the past 40 years, cloudiness seems to have increased. If this is in fact true, then this continual increase in cloudiness may lead to global climate change because it will change the amount of radiation entering and leaving the Earth's atmosphere. This characteristic of aircraft engine exhaust may act in a way similar to the effects produced by greenhouse gases.

Global radiative forcing from contrail cirrus
Aviation makes a significant contribution to anthropogenic climate forcing. The impacts arise from emissions of greenhouse gases, aerosols and nitrogen oxides, and from changes in cloudiness in the upper troposphere. An important but poorly understood component of this forcing is caused by ‘contrail cirrus’—a type of cloud that consist of young line-shaped contrails and the older irregularly shaped contrails that arise from them. Here we use a global climate model that captures the whole life cycle of these man-made clouds to simulate their global coverage, as well as the changes in natural cloudiness that they induce. We show that the radiative forcing associated with contrail cirrus as a whole is about nine times larger than that from line-shaped contrails alone. We also find that contrail cirrus cause a significant decrease in natural cloudiness, which partly offsets their warming effect. Nevertheless, net radiative forcing due to contrail cirrus remains the largest single radiative-forcing component associated with aviation. Our findings regarding global radiative forcing by contrail cirrus will allow their effects to be included in studies assessing the impacts of aviation on climate and appropriate mitigation options.

I hope by now you understand that it is not CO2 that can contribute to global warming. Contrails and cirrus contrails have large contribution too.

Sadly the current policy for contrails is:
Epa - contrails
Currently, there are no regulations addressing contrails and their atmospheric effects.

This is very sad. They enforce very tight CO2 control to the point of making many had become unemployed also industries and countries has to deal with very limited carbon credits.

And yet, they don't enforce the same enforcing effort to remedy contrails and contrail cirrus.

We should ask the government to at least monitor every airplane for their trails history. It would be better if government also willing to actually regulate trails from the airplane.

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