My 2p:
In truth no-one knows whether it's part of a natural process or man made (or aggravated by man). One thing to look at is the effect of carbon dioxide in the atmosphere. More CO2 = more heat... More heat = more water vapour in the air... More water vapour in the air = less heat... I don't believe that as a race we're doing good things to the planet but I don't believe there's enough evidence either way to say what's causing the rise in temperatures. It may only be anecdotal but the Romans planted vineyards in Yorkshire - the point is that both on the 'local' level and on the global level things change with or without man's influence.