Qantas Airways has started a green programme, called Fly Carbon Neutral Day, designed to offset carbon emissions on all flights on September 19.

Chief executive Geoff Dixon said the group's Fly Carbon Neutral Day will involve some 950 flights and 100,000 passengers.

"Qantas will pay to offset the equivalent of approximately 40,000 tonnes of greenhouse gases associated with these flights, with the money to be used to plant and maintain around 90,000 Mallee Eucalyptus trees," Mr Dixon said.

"These trees will not only sequester carbon from the atmosphere but will also aid in the prevention of salinity, erosion and soil degradation and provide income for farmers."

Mr Dixon said passengers could elect to offset their share of flight emissions by making a small contribution through qantas.com and jetstar.com.

Contributions will go to the Australia-based Greenhouse Friendly approved abatement programmes, which include energy efficiency measures, generation of renewable energy and tree planting projects. These programmes have been independently verified and subsequently authenticated by the Commonwealth Government's Australian Greenhouse Office.

Mr Dixon said the Qantas Group was focused on achieving a carbon dioxide savings target of more than two million tonnes by June 2011 through a range of environmental initiatives, including reducing fuel consumption.