The figure is calculated by measuring the total emissions of every flight leaving or arriving at UK airports and halving it. The rest of the emissions were the responsibility of the airports the other end.

Aviation represents 7% of the total CO₂ output for the whole country (36 million tonnes from a total of 568 million tonnes per year).

Now unless you have been in a cave, you would have heard that the Eyjafjallajokull volcano has grounded all UK planes for the last week.

I heard an idiot on the radio claiming recently that the volcano in Iceland has done an enormous amount of good for the environment due to grounded flights and was a good thing. It's true lots of C0₂ has been saved but the truth is the eco warriors haven't done the maths.

So I thought I would put them right.

The amount of CO₂ saved is 36mt / 52 = 0.7mt of CO₂. Put another way, the grounding of these planes has reduced the UK emissions by 0.1%.

Wow! No difference! Except for massive discomfort for 100,000 people.

The good news is the flights are back on ... and I'm off to Barcelona this weekend.