Here’s an interesting article that came out on the United Press International:
BERKELEY, Calif., Jan. 27 (UPI) — U.S. scientists say summer’s peak temperature and winter’s extreme low have shifted with the cycle of seasons and human activity might be the cause.

Not only has the average global temperature increased during the past 50 years, but the hottest day of the year has shifted nearly two days earlier, according to a study by the University of California-Berkeley and Harvard University.

Just as human-generated greenhouse gases appear to be the cause of global warming, human activity might also be the cause of the shift in the cycle of seasons, said graduate student Alexander Stine, first author of the report.

“We see 100 years where there is a very natural pattern of variability, and then we see a large departure from that pattern at the same time as global mean temperatures start increasing, which makes us suspect that there’s a human role here,” said Stine.

The research appears in the Jan. 22 issue of the journal Nature.