Ask Martin "Extra-terrestrial" Rees, Astronomer Royal, and Anthony "Third Way" Giddens in an op-ed in today's Times (yes - I bought it to read on a short rail journey).
Answer: nobody, you distinguished arseholes. It's been going on since the end of the Little Ice Age in the late 19th century.
"2010 is set to be the warmest year globally since records began". Who says so? The US National Oceanic and Atmospheric Association. When did its records begin? 1880.