The Correlation. Correlation is a measue of how close the line fits the points that you found in your experiment. Anyone can say whether they think the line is a good fit or not, but to measure it exactly, we use the correlation coefficient: R2.
As the seasons change and the amount of sunlight decreases, less chlorophyll is produced, and the leaves appear less green. Chlorophyll is broken down into simpler compounds at a constant rate, so green leaf color will gradually fade as chlorophyll production slows or stops.
Trees use temperature only as a secondary cue; if the fall is cool they hasten the development of their fall color, while if it is warm, they procrastinate and delay it. If global warming results in warmer fall temperatures, either during the day or night, this would tend to delay fall colors to later in the season.