“You can’t put a price on nature. You can’t quantify the uplifting effects of a walk in the Peak District or the way your soul soars at the sight of a stormy Cornish cliff. Except, it turns out you can: it’s worth almost £5 trillion a year. Economists have calculated the mental health benefits of the world’s national parks and concluded that on this measure alone they provide services amounting to a significant proportion of global GDP. And that is before you consider all the