A friend made the following comment to me – “Peter, go through the arithmetic, contrails are insignificant”.

Here is my reply – “Keith, that’s what I thought as well, but then I saw the sky filled with contrails while I was skiing and thought that doesn’t look insignificant. Then there’s research that suggests that things that look small can tip the balance for the planet. I don’t want to argue whether the research is correct or not, but I’m happy thinking that polluting a bit less can’t be a bad thing.”

And his response – “Yes, polluting a bit less is good, but don’t advocate a safe, low emission, efficient transport system unless you have something better. And certainly don’t do it because you looked up in the sky and saw contrails once. Look up now – any there? None here, lucky to see one a week here. And that’s the key. At any point on the earth at any time, there is very little. Contrails are orders of magnitude less than the daily noise level in cloud cover variation.”