It really doesn't matter where he himself was deliberately lying or whether he was merely lending the gravitas of his office to the deliberate lies of others. The point is that the President of the USA has access to any number of fact checkers and advisers and if he stands up and addresses the nation with a farrago of complete untruths then the buck stops with him. This dissembling and mendacity becomes all the more culpable when it forms the basis of major public policy decisions which will have a serious impact on people's lives in the US and beyond.

So why this snake-oil salesman being allowed to get away with it?

Here's the offending part of Obama's speech.

Now, it’s true that no single event makes a trend. But the fact is, the 12 hottest years on record have all come in the last 15. Heat waves, droughts, wildfires, floods, all are now more frequent and more intense. We can choose to believe that Superstorm Sandy, and the most severe drought in decades, and the worst wildfires some states have ever seen were all just a freak coincidence.