With its Geo-4 report, the United Nations tells us that most aspects of the Earth's natural environment are in decline; and that the decline will affect us, the planet's human inhabitants, in some pretty important ways.

Feel like you have heard it before? Of course you have, not least from the UN.

So what, you might ask, is special about this report? Why is it worth any more than a cursory headline glance before returning to the party?