After the New York A320 crash today maybe one should consider the effects of a similar incident off the end of the new proposed runway. The M25 would not be a pretty site.
Canary Warf would be less pretty than the M25, both to look at and for the economy as a whole.
Overall, there are a number of problems for the third runway including more flights, more pollution etc. BUT how does it benefit us?
Firstly, as has been said many times, this creates more jobs for the British economy which is fantastic however you look at it. It has been quoted at up to 100,000 people I believe?
Secondly, although we will probably see an increase in emissions in the short term due to increased flights, these will probably be reduced when the runway is completed when we would expect the 787 and 350 to be in full swing and new short haul aircraft in the air which should be more eco-friendly. Also, with a new runway it will reduce the time planes spent in the air waiting to line as smaller aircraft such as the A320 and B737 will be using the new runway which will make more room on the other runways increasing efficiency.
And, personally, I believe the most important factor is that Heathrow remains ahead of Paris CDG, Amsterdam Schiphol and Frankfurt Main. Heathrow is seen as the world's hub, although it is third in the list and it really needs to maintain it's status. This facility is a British necessity and no doubt benefits our economy most likely more than any other facility in the country. 000's of jobs are supported by Heathrow whether you are CEO of BAA or a taxi driver living in London.
The new runway will provide a number of problems but I believe for the sake of our economy, our welfare and our future, a third runway will pit the airport against Chicago and Atlanta for capacity and with Schipol and Changi for quality.