I went to hear Nicholas Stern speak a couple of nights ago: the subject was 'after Copenhagen'. It was a great talk; the man has the gift of speaking in a way that, written down, would make excellent reading. (A skill many politicians learn early.) But I was struck most forcefully again by timescales we now now talk about: what will happen in a hundred years? Current emission rates, according to climateinteractive, give a mean of 3.9 degrees. (OK, that's 90 years...) The spread's wide: if we're lucky, closer to 3, if we're unlucky, closer to 5. It hasn't been 5 degrees above current temperatures for 55 million years. Stern had a nice turn of phrase: these are the kind of changes that move people, move deserts, and are already manifesting as season creep (discussed in this recent paper that attempts a robust framework for analysing the impacts. No model in sight there: 30 years of data.)

One hundred years. Very few humans last that long. A hundred years ago, no first world war. The Los Angeles International Air Meet showcases some crazy new designs. The first commercial air-freight flight takes place - and the first commercial dirigible flight. (Now, this many flights happen in a 24 hour period.) Albania rises up against the Ottoman empire. George V becomes king. Wow - the Vatican makes all its priests take a compulsory oath against modernism. Mark Twain dies; 1.75 billion people live on.

It turns out the past is a different planet. Let's make a prediction: a hundred years hence, it'll be a different planet again.