1. Aircraft dim the sun
It was revealed after the events in New York and Washington on 11 September 2001 that, when there were very few aircraft in the skies above the United States, the intensity of solar radiation reaching the ground increased.

This was because high flying aircraft create a layer of haze in the atmosphere.

Another demonstration occurred after 15 April 2010 when an Icelandic volcano closed down jet air traffic all over Europe. For the first time in living memory completely clear skies appeared, uncrossed by jet trails. This must have increased the quantity of solar radiation available at ground level for heating water and generating electricity. (Research observations will report soon.) When flying resumed on 21 April the skies of southern England at once filled with linear clouds - though the weather remained the same (high pressure with clear skies).

This is of interest to those who use solar radiation for water heating and electricity. If the usual radiation is being cut by 10% (or more) they are getting less energy. This has a real cost as it means that 10% more capital equipment is needed to get the output desired.

It may also be of interest to us all as perhaps this dimming is slowing down the rate of global warming because some solar radiation is reflected back into space. But the airline industry is emitting vast and increasing amounts of carbon and nitrogen oxides, and thus is contributing to Warming.

2. Compensation.
In the ordinary legal system everyone who suffers a loss from others' activities is entitled to a compensation and an order to desist. As the use of solar energy increases, the cost is increasing.

I suggest that a National (or World) Association of Solar Energy Users should sue the airline industry for the losses they experience. The airline industry should pay a user fee for obscuring the sky over solar users. They should pass this cost on to their passengers. The money should go to owners of solar collecters. If fares rise, some people will find it better to use other modes of travel. For example, High Speed Rail will become more attractive (in countries where it exists).

There is room for elaboration of this concept before becoming law. Thus, should the compensation to be paid increase, the more solar collectors there are? In this case the more solar energy is collected, the more expensive aircraft emissions will become. Either the aviation industry will shrink or aircraft designers will find a way of not making clouds in the sky (is that possible?).

No doubt no payment will be made when overflying the sea. Thus one result may be to modify routing policy. Possibly flying will tend to be restricted to trans-oceanic routes, while overland transport is by rail.

 3. Fuel Taxes
The air industry was given exemption from fuel taxes at a time (1944) when it was very small and apparently negligible. Now that it is very large, the lack of taxes, which have to be paid by its competitors, distorts the market. Airlines should pay the same fuel taxes as other modes of transport - perhaps to a world taxation authority. The money raised should be used to invest in non-fossil fuels.

The vast increase of air travel in the last three decades is occurring without the industry and its passengers paying the environmental costs of their activities. The rapid growth of carbon and nitrogen oxides in the air causes the general climate change, but the haze that is also produced by the airline industry hinders the replacement of carbon fuels by solar energy because it increases by 10% the capital cost of solar collectors. Thus the industry is causing two aspects of the problem.