To put things into some level of proportion, information provided by the British Business and General Aviation Association (BBGA) demonstrates that, if emissions are proportioned equally to fuel usage, all general aviation flying activity in the world makes up just 0.02% of greenhouse gas emissions.
The UK's busiest airport, Heathrow, uses typically 22 million litres of jet fuel per day. A single Airbus A320 with the most efficient modern turbofan engines burns approximately 2,400 kg of fuel per engine per hour, or just over 6,000 litres per hour for both engines. The Cessna 172 type aircraft used on UKFlightExperiences flight services have an assumed fuel burn of 30 litres per hour, so we could have an equivalent of 200 sightseeing aircraft for every Airbus A320 in the sky. Heathrow's daily fuel usage could keep a Cessna 172 in the sky flying continuously for 83 years.
We aren't trying to say that this is Heathrow's problem and not ours - we all need to make our contribution. However, we need to visualise the order of magnitude and the amount of impact we can possibly make.
A single flight experience (of an average 1 hour 15 minutes duration) carrying 3 passengers would increase each passenger's carbon footprint by about 0.4% for the year, given the average UK carbon footprint per person per annum of 6.5 tonnes.
This small increase in carbon footprint has to be offset with the unmistakable need for light aircraft, flight training and flight experiences in inspiring, motivating and training the next generation of pilots. The aviation industry, if it was a country, would have a GDP high enough to place it in the G20; somewhere similar to the GDP of Indonesia or the Netherlands. This makes it a critical part of the world's economy without which the world would be a very different (and arguably even more polluted) place, since aviation has now surpassed other forms of transport (such as trucking) in the amount of cargo moved per kilometre per CO2 emitted.
In addition, a good, efficiently running engine, clean airframe, good maintenance disciplines and adherence to optimal climb & descent profiles reduce emissions as well as overall fuel burn.