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.

For example, oak trees in the Arnhem Forest of the Netherlands

now experience bud burst ten days earlier,

as compared to twenty years ago.

New oak leaves are a favorite food of winter moth caterpillars.

To survive, the caterpillars adapted

to the change in the tree's timing,

and now hatch 15 days earlier than before.

Migrating pied flycatcher birds, however,

aren't doing as well.

The birds prefer to feed their chicks winter moth caterpillars.

The caterpillars are now hatching earlier,

but the birds' chicks are not.

This delay is costing the birds a food source.

The pied flycatcher population has decreased

by up to 90% in some areas as a result.

Changes to a seemingly simple event,

leaves opening,

has ripple effects throughout a food web.

Earlier bloom times can also have an economic impact.

The famed cherry blossoms in Washington D.C.

are blooming five days earlier than before.

Since the cherry trees are blooming earlier,

the blossoms also fade earlier,

frustrating thousands of tourists who visit

for the Cherry Blossom Festival.

High school marching bands plan

all year to attend the parade

and perform, surrounded by a majestic white canopy.

How disappointing for them to find, well, trees

rather than the famous cherry blossoms!

Plants and animals react to changes in natural light and temperature.

Increasing temperatures cause plants to bloom earlier than before,

and become out of sync with the insects and birds in a food web.

So, the next time you look out your window

and notice what season it is,

you may be fooled by those blooming trees.

Think of phenology,

then think of how you can play a part to slow climate change.