I've been reading a book for quite a while - some bits of it I've read about six times!  Is this because the jokes are so good? or because I can't understand it? you might ask.

The answer is closer to the latter suggestion because there really aren't many jokes.  But the book is an absolute model of clarity - a real tour de force.  I keep re-reading bits because I am very keen to understand what it is telling me.

The book is Sustainable energy - without the hot air by David Mackay, an academic from Cambridge University.  It's not about climate change, though it is very relevant, but it is about renewable energy and whether it is feasible for us to produce enough energy from a combination of wasting less energy and producing more from nuclear, wind, solar, tidal etc. 

Every policy maker should read it - it should be compulsory for civil servants and ministers in the Department of Energy and Climate Change.  There are many interesting messages in the book - and although there aren't many jokes it is written in a very readable way (and it is all online) - and I'm sure I'll come back to some of them over the next few weeks.

But let's just start with a graph - I like graphs.  This graph shows how long a bit of carbon dioxide, a greenhouse gas, emitted now, will stay in the atmosphere.  Before you look at the graph - what's your guess for how much of a dollop of carbon dioxide will still be floating around in the atmosphere in 100 and 1000 years time?  Now have a look - how close were you?

Quite a lot isn't it? 

We all, I think, want to leave the world in a better state for our children and future generations.  Those dollops of carbon dioxide are quite a legacy - and quite a long-lasting legacy.