In Pictures: Autumn takes hold - Al Jazeera English

In Pictures: Autumn takes hold

Temperatures are dropping in the northern hemisphere and the trees are already changing colours.

Steff Gaulter | | Weather

At this time every year, the landscape across much of the Northern Hemisphere takes on a more colourful appearance.

The vibrant colours are caused by the disappearance of the green substance chlorophyll, which is produced when the leaves are producing energy for the tree.

As the days get shorter and the temperature drops, a cork-like substance forms at the base of each leaf. This cuts off the supply of water to the leaf, as well as the supply of energy back to the tree.

Without a supply of water, the chlorophyll disintegrates and colours that were in the leaves all along are suddenly visible.

Some leaves turn deep red or purple due to a pigment called anthocyanin, which also gives a purple colour to beetroot, red grapes and violets.

Carotene gives a leaf an orange colour, and this is the same substance which is also found in carrots and sweet potatoes.

And yellow leaves are caused by xanthophyll, which is also present in bananas and egg yolks.

The intensity and the longevity of the autumn colours varies each year, depending on the weather.

Strong winds of a large storm will strip the trees bare within minutes, as will an early frost.

If the second half of the summer is predominantly dry, and autumn is sunny and cool, then there is a strong likelihood that the leaves will turn a vivid colour.

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