I just find comfortable to link the gristmill site since it is are full of useful reliable scientific souces and charts.
The trend since 1998 is showed in SEVERAL of the links I already provided, you would do me a favour to read before posting, it's tiring and cumbersome to me to talk about the same thing again and again, and ultimately pointless if you don't read the answers I provide. Here it is again, with your theory nicely debunked:
http://gristmill.grist.org/story/2006/11/4/175028/329
And again about your old "warmer is better" theory:
http://gristmill.grist.org/story/2007/1/9/131657/6469