Madam, - David Sowby (August 30th) claims that hydrogen is a "fuel that will produce no harmful emissions" when used in aircraft.
Unfortunately for airline passengers, he is mistaken. When hydrogen is burned, it produces water, which would typically be harmless. At high altitudes, however, this water forms condensation, which leads to the development of cirrus clouds. While these clouds both trap and reflect heat, their net effect is to trap it, leading to increased warming of the planet.
Hydrogen-fuelled aircraft would be, by necessity, larger and would have to fly at higher altitudes than today's aircraft. This worsens the effect. The Royal Commission on Environmental Pollution estimates that a hydrogen-fuelled aircraft would have a climate-changing effect "some 13 times larger" than today's standard aircraft.
Hydrogen may well be the fuel of the future, but its useful application is limited to ground level. - Yours, etc,
MICHAEL PIDGEON, Brook Court, Monkstown, Co Dublin.