Take a look outside a window. What is the season where you are? How do you know? Most likely, you looked at a tree or plant and noticed details about its leaves and assessed the qualities of sunlight streaming outside. Observing the timing of biological events in relation to changes in season and climate is called "phenology". When you notice the daffodil buds are poking through the snow and think spring is on its way, you’re using phenology. When you see leaves turn from green to red, and watch migrating birds fly past, and realize that summer is over, autumn is here, you're using phenology. Literally meaning, "the science of appearance", phenology comes from the Greek words "pheno," to show or appear, and "logos," to study. Humans have relied on phenology since the time of hunters and gatherers. We've watched changes in seasons to know when to plant and harvest food and when to track migrating animals. Scientists observe and document seasonal changes in nature and look for patterns in the timing of seasonal events. Timing of these natural signs has remained consistent until recently. Increasing global temperature is causing rhythms of nature to shift. Bud burst the day when a tree or plant's leaf or flower buds open, is occurring earlier in the year for some species. For every one degree Celsius rise in temperature, bud burst happens five days earlier than usual. Differences in timing affect not only plants, but the insects and birds that depend on the plants for food.