If the case for climate change ever went on trial in a court of law, a jury might convict based on circumstantial evidence.
"Everywhere we look at land outside of the tropics, we see the same trend," Berkeley climatology PhD candidate Alexzander "Zan" Stine said.
Stine first noticed two years ago that some of the temperature data he was analyzing did not seem to fit.
"We found that the seasons are coming earlier and it's not just spring, but the whole year is shifting earlier," Stine said.
He saw it is coming earlier by a day and a half. It is a six percent shift in the timing of winter lows and summer highs, and all of the temperatures are warmer.
"It's the fact that the Earth is responding to the sun that is intriguing, here, and the fact that it is happening all over the land," Stine said.
When looking at the research, it is important to note the difference between weather and climate. Weather is short term, climate measures decades. Stine's study notes a change beginning in 1954.
The study shows that polar winds and the jet stream can influence the timing of seasons. But that's only part of the mechanism; there is another, unknown factor, at work. It may also be a case of warmer temperatures causing ground water to evaporate faster.
"So if you dried out that soil, there is less to heat up, and so it takes less time," Stine said. "The earth is getting warmer. It is clear that humans are involved in that and it is clear that humans are doing a lot to change how the earth behaves."