Tamino is a mathematician with an interest in climate science, he runs an excellent blog where he posts lucid introductions and analysis of some climate science issues. I've learned quite a bit from reading it.

Check out this recent post, it's a clear introduction to time series analysis, and in particular about how to use statistics to determine if there are trends in temperature data. I'd recommend the earlier parts to anyone who wants an understanding of what a trend is and isn't,...