I learned in my evolution class today that hotter, more tropical climates have less fluctations in temperature than do colder climates. Therefore, climate changes not just impact the average temperature but also the range of temperatures. And since wider temperature fluctuations can cause more variability in the supply of food, life becomes twice as hard for animals: once because its colder, and another time because food supply is not stable.

This double-impact is also in the relationship between mood swings and happiness. Emotional dips are bad in general, but the presence of high emotional instability also reduces the overall level of happiness. Therefore, emotional dips are a double-whammy.*

This parallel between happiness and temperature demonstrates the tight coupling in some systems between the variance and the average.

Why the climate changes are interesting for evolution:

Warmer rainforests covered Earth during the time period (early Paleocene 65-34 million years ago) when modern primates evolved. Because these rainforests also had less temperature fluctations, primates were therefore adapted to stable supplies of plants and fruits. When Earth's climate cooled in the Oligocene Era (34 million years ago), temperature fluctuations increased in colder regions, reducing flora tenability, and therefore making it difficult for primates to survive. Many of the primates went extinct except those living in existing rainforests and the newly evolved anthropoids (apes, chimps, humans). These anthropoids compensated with other evolved skills, such as social skills, to make up for the instability of food supply.

* Emotional highs do not have the same effect of raising the average; rather its the absolute fluctuation that affects the average.

On a separate note: I recognize that this is kind of a crackpot parallelism. I'm just appreciating the important relationship between variances and averages; usually we overlook how modifying the variance of a system can also have an impact on the average (and vice-versa).