It’s quite a contentious issue, and there are lots of political arguments about whether it exists and whether it is man-made or not. I don’t really know too much of the research that’s involved, and being a scientist at heart, I’m usually reluctant to come to a conclusion about something until I’ve learnt as much as I can about it. That being said, I think that the general scientific consensus is that we are in a period of higher-than-average temperatures, and it seems reasonable to suggest that man is probably having an impact upon that. As for how, I don’t know! What do you think?