It is "relatively cheap" to offset emissions from holiday flights, Mr Morley said in a speech on 21 July. "I would ask travellers to consider whether, in addition to enjoying their holidays, they counter some of the environmental damage by subscribing to one of the offset schemes available."
The Environment Department (DEFRA) explained that the aim was to raise awareness of air travel as a source of emissions, and let consumers know "they have the choice to offset if they wish".
But Mike Childs of Friends of the Earth said that Mr Morley was in danger of giving consumers the wrong priorities. "The focus has to be on reducing emissions in the first place," he said. Rather than suggesting you could "carry on flying and plant a few trees", offsetting should be an option "when you have gone as far as you can go with other reductions."
The Aviation Environment Federation, a campaign group, said: "We very much see [carbon offsetting] as a sideshow. It is not a substitute for regulation" in the form of taxes, charges or emissions trading. "We [do] see a role for carbon offset schemes," said the AEF's Tim Johnson. "They help to promote awareness of the issues and bring the message home," as regulatory action was unlikely before 2008 when the sector may enter the EU Emissions Trading Scheme.
But he questioned Mr Morley's claim that it would cost just £5 to offset the climate change effect of a flight to the Mediterranean. "As the science emerges I don't think we will see £5 added to a ticket," he said, noting that Swiss consultants INFRAS had calculated the environmental cost of air travel - including aspects such as noise - at nearer €50 per thousand miles.
Other AEF concerns were that such schemes were voluntary, and that the cost of offsetting varied widely between schemes. "Offset schemes are far from being an exact science," said Mr Johnson, so consumers would "have to do their homework."
Mr Morley named two UK offsetting companies in his speech, Future Forests and Climate Care. These companies have previously been listed, along with Friends of Conservation, by the Travel Foundation, part of the Government's sustainable tourism initiative.
The ministerial endorsement follows initiatives by many companies to use offsetting as a way of engaging consumers. So far, rumbles of discontent from environmental groups over the credibility of offsets - particularly those relying on forestry projects - have made little impact on enthusiasm for the approach (ENDS Report 356, pp 21-24 ).
In March, a scheme for Government Departments to offset the carbon impacts of their air travel was announced in the Government's sustainable development strategy, initially involving DEFRA, the Foreign Office and the Department for International Development. The scheme, to operate from April 2006, will go to tender once Departments' carbon emissions have been assessed. The Government is also committed to offsetting emissions relating to its G8 and EU Presidencies.
The airline industry has also committed itself to inform passenger understanding about the climate impacts of air travel, including "evaluating carbon offset initiatives as a practical short term measure". The proposal was one of 34 commitments in a strategy on sustainable aviation, produced by the UK's commercial aviation industry in July (ENDS Report 366, p 14 ).
So far the measure is being left to individual organisations. British Airways, for example, said it was "looking at addressing the impact we make on climate change". It would be considering carbon offsets among other options, a spokesperson said.
She said enquiries from individual passengers were "very hard to quantify" so it was difficult to tell whether they wanted to offset their flights. She said that it was relatively easy to pick up on enquiries from corporate customers. "Some of our larger customers are enquiring about it," she added.
BA Holidays, which trades separately from BA, is listed as a client of Climate Care, but it leaves it up to the consumer to follow up information: "We promote the website address," said a spokesperson, adding that it was printed "in the tourism and conservation guidelines - page 11" in the BA Holidays brochure. It has no information on whether its clients find or act on the information.
There is some evidence from elsewhere that when offsetting is made visible customers do take it up. Customers booking online with Avis Europe, for example, see a popup box asking whether they would like to make a £1 donation to Future Forests.
Responses are increasing, said Avis spokeswoman Hilary White: "In 2004 we had on average 90 customers a month. This year we have 150 per month." The company has also had "quite a lot of positive feedback, especially from countries like Germany".
Ms White said the company would like to extend the scheme to customers booking on site or on paper but the invoicing became too complex. Currently all the offsets are used in Future Forests' tree-planting schemes but Ms White said the company may move into other types of offsetting.