Last year the UK set new records for high temperatures in March, this year we have new record lows and unseasonal snow. Last Summer set new records for rainfall.

The reason - we are told - is that the jet stream is unstable due to the melting of the Arctic ice.

That is the key - instability.

In the past there have been long slow swings which gently slowed and reversed in most cases, though there were some fairly abrupt changes which are thought to be due to some event, a meteorite strike, a very large volcanic eruption which gave things a shove, but which were external to the system.

Anyone who has pushed a child on a swing knows about keeping a smooth oscillation going by applying a controlled force evenly over a distance - those who don't probably wonder why the authorities allow such dangerous items in playgrounds.

The amount of greenhouse gasses produced over the last hundred years is what is causing the swing to fly out from under us, and it is all down to luck if we are going to land on our head or our heels.